1
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Zavvou EE, Ramou E, Ahmed Z, Welch C, Mehl GH, Vanakaras AG, Karahaliou PK. Dipole-dipole correlations in the nematic phases of symmetric cyanobiphenyl dimers and their binary mixtures with 5CB. Soft Matter 2023; 19:9224-9238. [PMID: 37997929 DOI: 10.1039/d3sm01017a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2023]
Abstract
We report on the temperature dependence of birefringence and of the static dielectric permittivity tensor in a series of binary mixtures between the symmetric, bent-shaped, 1'',9''-bis(4-cyanobiphenyl-4'-yl)nonane (CB9CB) dimer and the monomeric nematogen 5CB. In the studied composition range the mixtures exhibit two nematic phases with distinct birefringence and dielectric features. Birefringence measurements are used to estimate the temperature dependence of the tilt between the axis defining the nanoscale helical modulation of the low temperature nematic phase with the (local) direction of the maximal alignment of the cyanobiphenyl units. Planar as well as magnetically and/or electrically aligned samples are used to measure the perpendicular and parallel components of the dielectric permittivity in both nematic phases. A self-consistent molecular field theory that takes into account flexibility and symmetry of the constituent mesogens is introduced for the calculation of order parameters and intra-molecular orientational dipolar correlations of the flexible dimers as a function of temperature/concentration. Utilising the tilt angle, as calculated from the birefringence measurements, and the predictions of the molecular theory, dielectric permittivity is modelled in the framework of the anisotropic version of the Kirkwood-Fröhlich theory. Using the inter-molecular Kirkwood correlation factors as adjustable parameters, excellent agreement between theory and permittivity measurements across the whole temperature range and composition of the mixtures is obtained. The importance of the orientational, intra- and inter-molecular, dipolar correlations, their relative impact on the static dielectric properties, as well as their connection with the local structure of the nematic phases of bent-shaped bimesogens, is discussed.
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Affiliation(s)
| | - Efthymia Ramou
- Department of Physics, University of Patras, 26504 Patras, Greece.
| | - Ziauddin Ahmed
- Department of Chemistry, University of Hull, HU6 7RX, UK
| | - Chris Welch
- Department of Chemistry, University of Hull, HU6 7RX, UK
| | - Georg H Mehl
- Department of Chemistry, University of Hull, HU6 7RX, UK
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2
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Yadav N, Panarin YP, Jiang W, Mehl GH, Vij JK. Spontaneous mirror symmetry breaking and chiral segregation in the achiral ferronematic compound DIO. Phys Chem Chem Phys 2023; 25:9083-9091. [PMID: 36919840 DOI: 10.1039/d3cp00357d] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2023]
Abstract
An achiral compound, DIO, known to exhibit three nematic phases namely N, NX and NF, is studied by polarizing microscopy and electro-optics for different surface conditions in confinement. The high temperature N phase assigned initially as a conventional nematic phase, shows two additional unusual features: the optical activity and the linear electro-optic response related to the polar nature of this phase. An appearance of chiral domains is explained by the spontaneous symmetry breaking arising from the saddle-splay elasticity and followed by the formation of helical domains of the opposite chirality. This is the first example of helical segregation observed in calamitic non-chiral molecules in the nematic phase. As reported previously, the ferronematic NF shows strong polar azimuthal surface interaction energy which stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and exhibits a twisted structure in cells with antiparallel buffing. The transmission spectra are simulated using Berreman's 4 × 4 matrix method. The observed agreement between the experimental and the simulated spectra quantitatively confirms the presence of twisted structures in antiparallel rubbed cells.
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Affiliation(s)
- Neelam Yadav
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland.
| | - Yuri P Panarin
- Department of Electrical and Electronic Engineering, TU Dublin, Dublin 7, Ireland
| | - Wanhe Jiang
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK
| | - Georg H Mehl
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK
| | - Jagdish K Vij
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland.
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3
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Yadav N, Panarin YP, Vij JK, Jiang W, Mehl GH. Two mechanisms for the formation of ferronematic phase in DIO as studied by dielectric spectroscopy. J Mol Liq 2023. [DOI: 10.1016/j.molliq.2023.121570] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2023]
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4
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Zhao YY, Li Y, Cao Y, Mehl GH, Liu F, Ungar G. The Effect of Mesogenic Coronas on the Type and Anisotropy of Gold Nanoparticle Superlattices: When Can the Tail Wag the Dog? Chemistry 2023; 29:e202203673. [PMID: 36573704 DOI: 10.1002/chem.202203673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Indexed: 12/28/2022]
Abstract
The correlation between the size of nanoparticles, the structure and shape of mesogenic ligands and the ensuing assembly behaviour is not really understood. Closer inspection shows very surprising features. Here, 2- and 4-nm gold nanoparticles (NPs) were synthesized, and grafted with a forked ligand containing two rod-like mesogens in its branches: one cholesterol, the other with azobenzene. The 4-nm NPs also contained n-hexylthiol as co-ligand. They were found to form a FCC cubic superlattice, whereas the 2-nm NPs form hexagonal HCP with weak birefringence, hence with partially oriented ligands. The structures were compared with those of related systems containing a range of different azobenzene-to-cholesterol ratios, all giving body-centred tetragonal superlattices with various degrees of anisotropy. Geometric analysis is presented in terms of the asphericity of the NPs' surroundings, requirement for space-filling and structural anisotropy. Some general rules are derived to help design the soft corona around the NPs in order to obtain superlattices with the desired structure and anisotropy.
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Affiliation(s)
- Yang-Yang Zhao
- Shaanxi International Research Center for Soft Matter, State Key Laboratory for Mechanical Behaviour of Materials, Xi'an Jiaotong University, Xi An Shi, Xi'an, 710049, P. R. China
| | - Yaxin Li
- School of Chemistry and Chemical Engineering, Henan University of Technology, Zhengzhou, 450001, P. R. China
| | - Yu Cao
- Shaanxi International Research Center for Soft Matter, State Key Laboratory for Mechanical Behaviour of Materials, Xi'an Jiaotong University, Xi An Shi, Xi'an, 710049, P. R. China
| | - Georg H Mehl
- Shaanxi International Research Center for Soft Matter, State Key Laboratory for Mechanical Behaviour of Materials, Xi'an Jiaotong University, Xi An Shi, Xi'an, 710049, P. R. China.,Department of Chemistry, University of Hull, Hull, HU6 7RX, UK
| | - Feng Liu
- Shaanxi International Research Center for Soft Matter, State Key Laboratory for Mechanical Behaviour of Materials, Xi'an Jiaotong University, Xi An Shi, Xi'an, 710049, P. R. China
| | - Goran Ungar
- Shaanxi International Research Center for Soft Matter, State Key Laboratory for Mechanical Behaviour of Materials, Xi'an Jiaotong University, Xi An Shi, Xi'an, 710049, P. R. China.,Department of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD, UK
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5
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Zhao Y, Li Y, Cao Y, Mehl GH, Liu F, Ungar G. The Effect of Mesogenic Coronas on the Type and Anisotropy of Gold Nanoparticle Superlattices: When Can the Tail Wag the Dog? Chemistry 2023. [DOI: 10.1002/chem.202300285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Yang‐yang Zhao
- Shaanxi International Research Center for Soft Matter State Key Laboratory for Mechanical Behaviour of Materials Xi'an Jiaotong University Xi An Shi Xi'an 710049 P. R. China
| | - Yaxin Li
- School of Chemistry and Chemical Engineering Henan University of Technology Zhengzhou 450001 P. R. China
| | - Yu Cao
- Shaanxi International Research Center for Soft Matter State Key Laboratory for Mechanical Behaviour of Materials Xi'an Jiaotong University Xi An Shi Xi'an 710049 P. R. China
| | - Georg H. Mehl
- Shaanxi International Research Center for Soft Matter State Key Laboratory for Mechanical Behaviour of Materials Xi'an Jiaotong University Xi An Shi Xi'an 710049 P. R. China
- Department of Chemistry University of Hull Hull HU6 7RX UK
| | - Feng Liu
- Shaanxi International Research Center for Soft Matter State Key Laboratory for Mechanical Behaviour of Materials Xi'an Jiaotong University Xi An Shi Xi'an 710049 P. R. China
| | - Goran Ungar
- Shaanxi International Research Center for Soft Matter State Key Laboratory for Mechanical Behaviour of Materials Xi'an Jiaotong University Xi An Shi Xi'an 710049 P. R. China
- Department of Materials Science and Engineering University of Sheffield Sheffield S1 3JD UK
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6
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Thoen J, Cordoyiannis G, Jiang W, Mehl GH, Glorieux C. Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic, and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry. Phys Rev E 2023; 107:014701. [PMID: 36797863 DOI: 10.1103/physreve.107.014701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Accepted: 12/21/2022] [Indexed: 06/18/2023]
Abstract
High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular, adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity c_{p}(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a low-temperature ferroelectric nematic phase (N_{F}) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (N_{x}). From the detailed data of h(T) and c_{p}(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (x_{DIO}). The x_{DIO} dependence on the transition temperatures for both transitions could be well described by a quadratic function. Both these transitions were weakly first order. The true latent heat of the N_{x}-N transition of DIO was as low as L=0.0075±0.0005J/g and L=0.23±0.03J/g for the N_{F}-N_{x} transition, which is about twice the previously reported value of 0.115 J/g for the N_{F}-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing x_{DIO}. At all the N_{x}-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the N_{F} to the higher-temperature phase exhibits substantial pretransitional behavior, in particular, in the high-temperature phase. Power-law analysis of c_{p}(T) resulted in an effective critical exponent α=0.88±0.1 for DIO and this value decreased in the mixtures with decreasing x_{DIO} toward α=0.50±0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis.
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Affiliation(s)
- J Thoen
- Laboratory for Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
| | - G Cordoyiannis
- Condensed Matter Physics Department, Jožef Stefan Institute, 1000 Ljubljana, Slovenia
| | - W Jiang
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - C Glorieux
- Laboratory for Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
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7
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Merkel K, Loska B, Arakawa Y, Mehl GH, Karcz J, Kocot A. How Do Intermolecular Interactions Evolve at the Nematic to Twist–Bent Phase Transition? Int J Mol Sci 2022; 23:ijms231911018. [PMID: 36232324 PMCID: PMC9570452 DOI: 10.3390/ijms231911018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Revised: 09/15/2022] [Accepted: 09/18/2022] [Indexed: 11/30/2022] Open
Abstract
Polarized beam infrared (IR) spectroscopy provides valuable information on changes in the orientation of samples in nematic phases, especially on the role of intermolecular interactions in forming the periodically modulated twist–bent phase. Infrared absorbance measurements and quantum chemistry calculations based on the density functional theory (DFT) were performed to investigate the structure and how the molecules interact in the nematic (N) and twist–bend (NTB) phases of thioether dimers. The nematic twist–bend phase observed significant changes in the mean IR absorbance. On cooling, the transition from the N phase to the NTB phase was found to be accompanied by a marked decrease in absorbance for longitudinal dipoles. Then, with further cooling, the absorbance of the transverse dipoles increased, indicating that transverse dipoles became correlated in parallel. To investigate the influence of the closest neighbors, DFT calculations were performed. As a result of the optimization of the molecular cores system, we observed changes in the square of the transition dipoles, which well corresponds to absorbance changes observed in the IR spectra. Interactions of molecules dominated by pairing were observed, as well as the axial shift of the core to each other.
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Affiliation(s)
- Katarzyna Merkel
- Institute of Materials Engineering, Faculty of Science and Technology, University of Silesia, ul. 75 Pułku Piechoty, 41-500 Chorzów, Poland
| | - Barbara Loska
- Institute of Materials Engineering, Faculty of Science and Technology, University of Silesia, ul. 75 Pułku Piechoty, 41-500 Chorzów, Poland
| | - Yuki Arakawa
- Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan
| | - Georg H. Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - Jakub Karcz
- Faculty of Advanced Technologies and Chemistry, Military University of Technology, 00-908 Warszawa, Poland
| | - Antoni Kocot
- Institute of Materials Engineering, Faculty of Science and Technology, University of Silesia, ul. 75 Pułku Piechoty, 41-500 Chorzów, Poland
- Correspondence: ; Tel.: +48-32-3497630
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8
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Kocot A, Loska B, Arakawa Y, Mehl GH, Merkel K. Study of the Experimental and Simulated Vibrational Spectra Together with Conformational Analysis of Thioether Cyanobiphenyl-Based Liquid Crystal Dimers. Int J Mol Sci 2022; 23:ijms23148005. [PMID: 35887352 PMCID: PMC9316788 DOI: 10.3390/ijms23148005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 07/15/2022] [Accepted: 07/18/2022] [Indexed: 11/16/2022] Open
Abstract
Infrared spectroscopy (IR) and quantum chemistry calculations that are based on the density functional theory (DFT) have been used to study the structure and molecular interactions of the nematic and twist-bend phases of thioether-linked dimers. Infrared absorbance measurements were conducted in a polarized beam for a homogeneously aligned sample in order to obtain more details about the orientation of the vibrational transition dipole moments. The distributions to investigate the structure and conformation of the molecule dihedral angle were calculated. The calculated spectrum was compared with the experimental infrared spectra and as a result, detailed vibrational assignments are reported.
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Affiliation(s)
- Antoni Kocot
- Institute of Materials Engineering, Faculty of Science and Technology, University of Silesia, ul. 75. Pułku Piechoty, 41-500 Chorzów, Poland; (A.K.); (B.L.)
| | - Barbara Loska
- Institute of Materials Engineering, Faculty of Science and Technology, University of Silesia, ul. 75. Pułku Piechoty, 41-500 Chorzów, Poland; (A.K.); (B.L.)
| | - Yuki Arakawa
- Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan;
| | - Georg H. Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK;
| | - Katarzyna Merkel
- Institute of Materials Engineering, Faculty of Science and Technology, University of Silesia, ul. 75. Pułku Piechoty, 41-500 Chorzów, Poland; (A.K.); (B.L.)
- Correspondence: ; Tel.: +48-32-349-7630
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9
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Fells JAJ, Salter PS, Welch C, Jin Y, Wilkinson TD, Booth MJ, Mehl GH, Elston SJ, Morris SM. Dynamic phase measurement of fast liquid crystal phase modulators. Opt Express 2022; 30:24788-24803. [PMID: 36237024 DOI: 10.1364/oe.460083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Accepted: 05/25/2022] [Indexed: 06/16/2023]
Abstract
We present dynamic time-resolved measurements of a multi-pixel analog liquid crystal phase modulator driven at a 1 kHz frame rate. A heterodyne interferometer is used to interrogate two pixels independently and simultaneously, to deconvolve phase modulation with a wide bandwidth. The root mean squared optical phase error within a 30 Hz to 25 kHz bandwidth is <0.5° and the crosstalk rejection is 50 dB. Measurements are shown for a custom-built device with a flexoelectro-optic chiral nematic liquid crystal. However, the technique is applicable to many different types of optical phase modulators and spatial light modulators.
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10
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Zhao Y, Cao Y, Siligardi G, Mehl GH, Liu F, Ungar G. Cover Picture. Chem Asian J 2022. [DOI: 10.1002/asia.202200167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Yang‐yang Zhao
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter Xi'an Jiaotong University Xi'an 710049 P. R. China
| | - Yu Cao
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter Xi'an Jiaotong University Xi'an 710049 P. R. China
| | | | - Georg H. Mehl
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter Xi'an Jiaotong University Xi'an 710049 P. R. China
- Department of Chemistry University of Hull Hull HU6 7RX United Kingdom
| | - Feng Liu
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter Xi'an Jiaotong University Xi'an 710049 P. R. China
| | - Goran Ungar
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter Xi'an Jiaotong University Xi'an 710049 P. R. China
- Department of Materials Science and Engineering University of Sheffield Sheffield S1 3JD United Kingdom
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11
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Zhao YY, Cao Y, Siligardi G, Mehl GH, Liu F, Ungar G. Self-assembly of gold nanoparticles into an adjustable plasmonic 3D lattice using Janus-type forked mesogenic ligands. Chem Asian J 2022; 17:e202200057. [PMID: 35192226 DOI: 10.1002/asia.202200057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 02/21/2022] [Indexed: 11/06/2022]
Abstract
We report the formation of a 3D body-centred self-assembled superlattice of gold nanoparticles whose interparticle gap, and hence its plasmonic properties, are adjustable exclusively in the xy -plane. Thus, even though the particles are spherical, their anisotropic packing generates tailorable plasmonic dichroism. The gold nanoparticles are coated with forked ligands containing two mesogens: either two cholesterols ("twin"), one cholesterol and one azobenzene ("Janus"), or a mixture of the two. Beside the body-centered arrangement of gold nanoparticles, the structure also contains unusual two-dimensionally modulated smectic-like layers of mesogens in an egg-box geometry. Moreover, the presence of azobenzene mesogens allows the superlattice to be melted through UV-induced photo-isomerization; the process is reversible displaying low fatigue on repeated cycling.
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Affiliation(s)
- Yang-Yang Zhao
- Xi'an Jiaotong University, Department of Chemistry, School of Science, West Xianning Road, 710049, Xi'an, CHINA
| | - Yu Cao
- Xi'an Jiaotong University, Department of Chemistry, School of Science, CHINA
| | | | - Georg H Mehl
- University of Hull, Department of Chemistry, UNITED KINGDOM
| | - Feng Liu
- Xi'an Jiaotong University, Department of Chemistry, School of Science, CHINA
| | - Goran Ungar
- University of Sheffield, Materials Science and Engineering, Sir Robert Hadfield Building, Mappin Street, S1 3JD, Sheffield, UNITED KINGDOM
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12
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Saha R, Feng C, Welch C, Mehl GH, Feng J, Zhu C, Gleeson J, Sprunt S, Jákli A. The interplay between spatial and heliconical orientational order in twist-bend nematic materials. Phys Chem Chem Phys 2021; 23:4055-4063. [PMID: 33587066 DOI: 10.1039/d0cp06633h] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The helical pitch formed by organic molecules, such as the α-helix of proteins, usually requires hydrogen bonding between chiral units and long-range positional order. It was recently found that certain liquid crystal oligomers can have a twist-bend nematic (NTB) phase with nanoscale heliconical structure without hydrogen bonding, molecular chirality or positional order. To understand the nature of this unique structure, here we present hard and resonant tender X-ray scattering studies of two novel sulfur containing dimer materials. We simultaneously measure the temperature dependences of the helical pitch and the correlation length of both the helical and positional order. In addition to an unexpected strong variation of the pitch with the length of the spacer connecting the monomer units, we find that at the transition to the NTB phase the positional correlation length drops. The helical structure was found not only in the NTB phase but observed even in the upper range of a smectic phase that forms just below the NTB state. The coexistence of smectic layering and the heliconical order indicates a layered (SmATB) phase wherein the rigid units of the dimers are tilted with respect to the smectic layer normal in order to accommodate the bent conformation of the dimers and the tilt direction rotates along the heliconical axis.
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Affiliation(s)
- R Saha
- Department of Physics, Kent State University, Kent, OH 44242, USA.
| | - C Feng
- Materials Science Graduate Program, Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA and Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA
| | - C Welch
- Department of Chemistry, University of Hull, Hull, UK
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull, UK
| | - J Feng
- Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA
| | - C Zhu
- Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA
| | - J Gleeson
- Department of Physics, Kent State University, Kent, OH 44242, USA.
| | - S Sprunt
- Department of Physics, Kent State University, Kent, OH 44242, USA. and Materials Science Graduate Program, Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA
| | - A Jákli
- Department of Physics, Kent State University, Kent, OH 44242, USA. and Materials Science Graduate Program, Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA
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13
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Merkel K, Loska B, Welch C, Mehl GH, Kocot A. Molecular biaxiality determines the helical structure - infrared measurements of the molecular order in the nematic twist-bend phase of difluoro terphenyl dimer. Phys Chem Chem Phys 2021; 23:4151-4160. [PMID: 33564811 DOI: 10.1039/d1cp00187f] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Fourier-transform infrared polarized spectroscopy was employed, to obtain the three components of the infrared absorbance for a series of bent-shaped dimers containing double fluorinated terphenyl core (DTC5Cn, n = 5, 7, 9, 11). The data were used to calculate both uniaxial and biaxial order parameters, for various molecular groups of dimers. The molecule bend was estimated based on the observed differences between the uniaxial order parameters for the terphenyl core and central hydrocarbon linker. The orientational order, distinctly reverses its monotonic trend of increase to decrease at the transition temperature, from the uniaxial nematic to the twist-bend nematic phase as result of the director tilt in latter/(twist-bend) phase. The molecular biaxiality, which is negligible in the nematic phase, starts increasing on entering the twist-bend nematic phase, following a sin-square relationships with the tilt angle. The local director curvature is found to be controlled by the molecular biaxiality parameter.
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Affiliation(s)
- Katarzyna Merkel
- Institute of Materials Engineering, University of Silesia, 75 Pułku Piechoty 1A, 41-500 Chorzów, Poland.
| | - Barbara Loska
- Institute of Materials Engineering, University of Silesia, 75 Pułku Piechoty 1A, 41-500 Chorzów, Poland.
| | - Chris Welch
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - Georg H Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - Antoni Kocot
- Institute of Materials Engineering, University of Silesia, 75 Pułku Piechoty 1A, 41-500 Chorzów, Poland.
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14
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Crapnell R, Alhasan HS, Partington LI, Zhou Y, Ahmed Z, Altalhi AA, Varley TS, Alahmadi N, Mehl GH, Kelly SM, Lawrence NS, Marken F, Wadhawan JD. Electrochemically Induced Mesomorphism Switching in a Chlorpromazine Hydrochloride Lyotropic Liquid Crystal. ACS Omega 2021; 6:4630-4640. [PMID: 33644569 PMCID: PMC7905802 DOI: 10.1021/acsomega.0c05284] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Accepted: 12/18/2020] [Indexed: 06/12/2023]
Abstract
The discovery of electrochemical switching of the Lα phase of chlorpromazine hydrochloride in water is reported. The phase is characterized using polarizing microscopy, X-ray scattering, rheological measurements, and microelectrode voltammetry. Fast, heterogeneous oxidation of the lyotropic liquid crystal is shown to cause a phase change resulting from the disordering of the structural order in a stepwise process. The underlying molecular dynamics is considered to be a cooperative effect of both increasing electrostatic interactions and an unfolding of the monomers from "butterfly"-shaped in the reduced form to planar in the oxidized form.
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Affiliation(s)
- Robert
D. Crapnell
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Huda S. Alhasan
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Lee I. Partington
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Yan Zhou
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Ziauddin Ahmed
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Amal A. Altalhi
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Thomas S. Varley
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Nadiyah Alahmadi
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Georg H. Mehl
- Department
of Chemistry, University of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, United Kingdom
| | - Stephen M. Kelly
- Organic
and Materials Chemistry, Department of Chemistry, Liquid Crystals
and Organophotonics Research Group, University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, United Kingdom
| | - Nathan S. Lawrence
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
| | - Frank Marken
- Department
of Chemistry, University of Bath, Claverton Down, Bath BA2
7AY, United Kingdom
| | - Jay D. Wadhawan
- Department
of Physical Sciences (Chemistry), University
of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, Humberside, United Kingdom
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15
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Merkel K, Loska B, Welch C, Mehl GH, Kocot A. The role of intermolecular interactions in stabilizing the structure of the nematic twist-bend phase. RSC Adv 2021; 11:2917-2925. [PMID: 35424219 PMCID: PMC8693785 DOI: 10.1039/d0ra10481g] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2020] [Accepted: 01/04/2021] [Indexed: 12/20/2022] Open
Abstract
The understanding of the relationship between molecular structure and the formation of the nematic twist-bend phase is still at an early stage of development. This is mainly related to molecular geometry, while the correlation between the nematic twist-bend phase and the electronic structure is ambiguous. To explore the electronic effect on properties and stabilization of the nematic twist-bend phase we investigated 2′,3′-difluoro-4,4′′-dipentyl-p-terphenyl dimers (DTC5Cn). We used polarized fourier transform infrared spectroscopy, which can, at least in principle, provide information about the ordering in the twist-bend phase. All dimers show a significant drop in the average value of the transition dipole moment for parallel dipoles at the transition from the nematic to the twist-bend phase, and an increase for perpendicular dipoles, despite remaining unchanged for the monomer. Density functional theory calculations were used to determine the geometric and electronic properties of the hydrogen bonded complexes. We have provided experimental and theoretical evidence of stabilization of the nematic twist-bend phase by arrays of multiple hydrogen bonds (XF⋯HX, X–benzene ring). Stabilization of the nematic twist-band phase by arrays of multiple nonspecific short-range intermolecular interactions.![]()
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Affiliation(s)
- Katarzyna Merkel
- Institute of Materials Engineering, University of Silesia 75 Pułku Piechoty 1A 41-500 Chorzów Poland
| | - Barbara Loska
- Institute of Materials Engineering, University of Silesia 75 Pułku Piechoty 1A 41-500 Chorzów Poland
| | - Chris Welch
- Department of Chemistry, University of Hull Hull HU6 7RX UK
| | - Georg H Mehl
- Department of Chemistry, University of Hull Hull HU6 7RX UK
| | - Antoni Kocot
- Institute of Materials Engineering, University of Silesia 75 Pułku Piechoty 1A 41-500 Chorzów Poland
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16
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Yu H, Qu W, Liu F, Mehl GH. Two helices from one chiral centre - self organization of disc shaped chiral nanoparticles. Chem Sci 2020; 12:1778-1782. [PMID: 34163939 PMCID: PMC8179125 DOI: 10.1039/d0sc05100d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 11/30/2020] [Indexed: 11/21/2022] Open
Abstract
Gold nanoparticles (AuNPs) have been prepared and surface-functionalized with a mixture of 1-hexanethiol co-ligands and chiral discogen ligands separated from a disulfide function via a flexible spacer. Polarized optical microscopy together with differential scanning calorimetry showed that the organic corona of the nanocomposite forms a stable chiral discotic nematic phase with a wide thermal range. Synchrotron X-ray diffraction showed that gold NPs form a superlattice with p2 plane symmetry. Analysis indicated that the organic corona takes up the shape of a flexible macrodisk. Synchrotron radiation-based circular dichroism signals of thin films are significantly enhanced on the isotropic-LC transition, in line with the formation of a chiral nematic phase of the organic corona. At lower temperatures the appearance of CD signals at longer wavelengths is associated with the chiral organisation of the NPs and is indicative of the formation of a second helical structure. The decreased volume required and the chiral environment of the disc ligands drives the nanoparticles into columns that arrange helically, parallel to the shortest axis of the two dimensional lattice.
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Affiliation(s)
- Huanan Yu
- Department of Chemistry, University of Hull Hull HU6 7RX UK
| | - Wentao Qu
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Centre for Soft Matter, Xi'an Jiaotong University Xi'an P. R. China
| | - Feng Liu
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Centre for Soft Matter, Xi'an Jiaotong University Xi'an P. R. China
| | - Georg H Mehl
- Department of Chemistry, University of Hull Hull HU6 7RX UK
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Centre for Soft Matter, Xi'an Jiaotong University Xi'an P. R. China
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17
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Krishnasamy V, Qu W, Chen C, Huo H, Ramanagul K, Gothandapani V, Mehl GH, Zhang Q, Liu F. Self-Assembly and Temperature-Driven Chirality Inversion of Cholesteryl-Based Block Copolymers. Macromolecules 2020. [DOI: 10.1021/acs.macromol.9b02264] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Velmurugan Krishnasamy
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter, Xi’an Jiaotong University, Xi’an 710049, P. R. China
| | - Wentao Qu
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter, Xi’an Jiaotong University, Xi’an 710049, P. R. China
| | - Changlong Chen
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter, Xi’an Jiaotong University, Xi’an 710049, P. R. China
| | - Haohui Huo
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter, Xi’an Jiaotong University, Xi’an 710049, P. R. China
| | | | | | - Georg H. Mehl
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter, Xi’an Jiaotong University, Xi’an 710049, P. R. China
- Department of Chemistry, University of Hull, Hull HU6 7RX, U.K
| | - Qilu Zhang
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter, Xi’an Jiaotong University, Xi’an 710049, P. R. China
| | - Feng Liu
- State Key Laboratory for Mechanical Behaviour of Materials, Shaanxi International Research Center for Soft Matter, Xi’an Jiaotong University, Xi’an 710049, P. R. China
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18
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Yip WC, Welch C, Mehl GH, Wilkinson TD. Analog modulation by the flexoelectric effect in liquid crystals. Appl Opt 2020; 59:2668-2673. [PMID: 32225814 DOI: 10.1364/ao.386096] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 01/28/2020] [Indexed: 06/10/2023]
Abstract
We have solved the long-standing problems of stability and hysteresis, and we are able to obtain the homogeneous uniform lying helix structure in polymer-free cholesteric liquid crystals. This is instrumental for the present work to demonstrate the analog modulation at high speed and high precision. The device is configured for the transverse field switching wherein the substrate surface is flat. In addition to the response time of 10 ms at room temperature, we have obtained the R-squared and the adjusted R-squared as a measure of true sine wave for the sinusoidal responding transmissions from 1 Hz to 100 kHz that are all greater than 0.9993. In a Michelson interferometer, the phase shift at wavelength 633 nm after two passes has been measured to be equal to about $\pi /{9}$π/9 at 4.6 V/µm for the chiral-doped nematic mixtures E7.
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19
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20
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Merkel K, Welch C, Ahmed Z, Piecek W, Mehl GH. Dielectric response of electric-field distortions of the twist-bend nematic phase for LC dimers. J Chem Phys 2019; 151:114908. [PMID: 31542029 DOI: 10.1063/1.5114824] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Wide band dielectric spectroscopy of bent-shaped achiral liquid-crystal dimers 1″-n″-bis(4-cyanobiphenyl-4'-yl) n-alkanes (CBnCB n = 7, 9, 11) has been investigated in a frequency range 0.1 Hz-100 MHz using planar-aligned cells of sample thicknesses ranging from 2 to 10 (μm) over a temperature range that covers both nematic and twist bend nematic phases. Two peaks in the dielectric spectrum in the higher frequency range are assigned to the molecular relaxation processes. The peak at the highest frequency, ∼40 to 80 MHz, is assigned to an internal precessional rotation of a single unit of the dimer around the director. The mode in the next lower frequency range of 2-10 MHz is assigned to the spinning rotation of the dimer around its long axis. This involves fluctuations of the dipole moment of the bent-shaped conformation that is directed along its arrow direction of the bow shape formed by the dimer. The peak in the frequency range 100 kHz-1 MHz can be assigned to the collective fluctuations of the local director with reference to the helical axis of the NTB structure. The dependence of its frequency on temperature is reminiscent of the soft mode observed at the SmA* to SmC* phase transition. This result clearly corresponds to the electro-clinic effect-the response of the director to the applied electric field in an electro-optic experiment. The lowest frequency mode, observed in the frequency range of 0.1 Hz-100 Hz, is identified with the Goldstone mode. This mode is concerned with the long range azimuthal angle fluctuations of the local director. This leads to an alternating compression and expansion of the periodic structure of the NTB phase.
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Affiliation(s)
- K Merkel
- Faculty of Computer Science and Material Science, Institute of Technology and Mechatronics, University of Silesia in Katowice, Katowice, Poland
| | - C Welch
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - Z Ahmed
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - W Piecek
- Faculty of Advanced Technologies and Chemistry, Military University of Technology, Warszawa, Poland
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
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21
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Fells JAJ, Welch C, Yip WC, Elston SJ, Booth MJ, Mehl GH, Wilkinson TD, Morris SM. Dynamic response of large tilt-angle flexoelectro-optic liquid crystal modulators. Opt Express 2019; 27:15184-15193. [PMID: 31163718 DOI: 10.1364/oe.27.015184] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Accepted: 04/30/2019] [Indexed: 06/09/2023]
Abstract
We present here the first time-resolved tilt-angle and retardance measurements for large-tilt (>45°) flexoelectro-optic liquid crystal modulators. These devices have potential for next generation fast switching (>1 kHz), 0-2π analog phase spatial light modulators (SLMs), with applications in optical beamsteering, microscopy and micromachining. The chiral nematic device used consisted of a mixture of CBC7CB and the chiral dopant R5011 in a nominally 5 µm-thick cell, aligned in the uniform lying helix mode. As the device is dynamically switched over angles of ± 54°, retardance changes of up to 0.17λ are observed. Furthermore, the time-resolved measurements reveal an asymmetry in the tilt in the optic-axis depending on the polarity of the applied electric field. The change in the optic-axis exhibits a pattern dependence, whereby it is determined by both the pulse history and the applied field. This pattern dependence results in tilt-angle errors of up to 8.8°, which could manifest as phase errors as large as 35.2° in potential SLMs. These time domain measurements may allow correction of these deterministic errors, to realize practical devices.
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22
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Wang X, Fells JAJ, Yip WC, Ali T, Lin JD, Welch C, Mehl GH, Booth MJ, Wilkinson TD, Morris SM, Elston SJ. Fast and low loss flexoelectro-optic liquid crystal phase modulator with a chiral nematic reflector. Sci Rep 2019; 9:7016. [PMID: 31064999 PMCID: PMC6504954 DOI: 10.1038/s41598-019-42831-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2018] [Accepted: 04/05/2019] [Indexed: 11/09/2022] Open
Abstract
In this paper, we demonstrate a flexoelectro-optic liquid crystal phase-only device that uses a chiral nematic reflector to achieve full 2π phase modulation. This configuration is found to be very tolerant to imperfections in the chiral nematic reflector provided that the flexoelectro-optic LC layer fulfils the half-wave condition. Encouragingly, the modulation in the phase, which operates at kHz frame rates, is also accompanied by low amplitude modulation. The configuration demonstrated herein is particularly promising for the development of next-generation liquid crystal on silicon spatial light modulators.
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Affiliation(s)
- Xiuze Wang
- Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK
| | - Julian A J Fells
- Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK
| | - Wing C Yip
- Department of Engineering, University of Cambridge, Cambridge, CB3 0FA, UK
| | - Taimoor Ali
- Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK
| | - Jia-de Lin
- Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK
| | - Chris Welch
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK
| | - Georg H Mehl
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK
| | - Martin J Booth
- Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK
| | | | - Stephen M Morris
- Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK.
| | - Steve J Elston
- Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK.
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23
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Aluculesei A, Cachitas H, Carvalho J, Vaca Chavez F, Figueirinhas JL, Sebastião PJ, Cruz C, Tamba MG, Kohlmeier A, Mehl GH. 1H NMR study of molecular order and dynamics in the liquid crystal CB-C9-CB. Phys Chem Chem Phys 2019; 21:4523-4537. [PMID: 30735227 DOI: 10.1039/c8cp06868b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Molecular order and dynamics of the CB-C9-CB liquid crystalline dimer exhibiting the nematic (N) and the twist bend nematic (Ntb) phases were investigated by proton NMR spectroscopy, using fields of 0.78 T and 7.04 T, and relaxometry. The first relaxometry experiments for a very wide Larmor frequency domain (8 kHz-300 MHz) on this system, using a combination of standard and fast field cycling NMR techniques, were performed. The spectroscopy results in the Ntb phase allowed us to probe the local molecular orientation relative to the Ntb helix axis. The relaxation data were analyzed considering order director fluctuations (ODF), molecular self-diffusion (SD) and local molecular rotations/reorientations (R) relaxation mechanisms. Global fits of theoretical relaxation models, as a function of temperature and Larmor frequency, for the phases under investigation, allowed for the determination of rotational correlation times, diffusion coefficients, viscoelastic parameters, correlation lengths and activation energies (in the case of thermally activated mechanisms). A clear difference between the structures of the N and Ntb phases was detected from the results of proton spin-lattice relaxation through distinct temperature and frequency dependencies' signatures of the collective modes. Significant pre-transitional effects were observed at the N-Ntb phase transition both from relaxometry and spectroscopy data. The experimental results correlate to data and models for comparable liquid crystalline systems.
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Affiliation(s)
- Alina Aluculesei
- Centro de Física e Engenharia de Materiais Avançados, Dept. of Physics, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal.
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24
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Cheng F, Verrelli E, Alharthi FA, Kelly SM, O'Neill M, Kemp NT, Kitney SP, Lai KT, Mehl GH, Anthopoulos T. Lyotropic 'hairy' TiO 2 nanorods. Nanoscale Adv 2019; 1:254-264. [PMID: 36132481 PMCID: PMC9473231 DOI: 10.1039/c8na00054a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 07/19/2018] [Indexed: 06/15/2023]
Abstract
We report the synthesis of the first stable, solution-processable and photocrosslinkable hybrid organic/inorganic titanium dioxide nanorods as 'hairy rods' coated with phosphonate ligands with photoreactive coumarin groups located in a terminal position. The relationships between the chemical structure of the diethyl-ω-[(7-oxycoumaryl)-n-alkyl]phosphonate ligands on the ligand exchange rate (LER) and the solubility of the resultant ligand-stabilized titanium dioxide nanorods in organic solvents are elucidated. These TiO2 nanorods, with an organic ligand coating, are short enough (aspect ratio = 5-8) to be dissolved in chlorobenzene at high concentrations, but long enough to form lyotropic nematic liquid crystals. These colloidal solutions are used to deposit a thin, uniform layer of hybrid organic/inorganic TiO2 nanorods with their long axes in the plane of a flat, smooth substrate through a self-organization process. Standard photolithographic patterning creates an insoluble dielectric layer of the desired thickness, smoothness and uniformity and with a dielectric constant of sufficient magnitude, k = 8, suitable for the fabrication of multilayer, plastic electronic devices using solution-based fabrication techniques, such as ink-jet printing, used in roll-to-roll manufacturing.
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Affiliation(s)
- Fei Cheng
- School of Mathematics & Physical Sciences, University of Hull Cottingham Road Hull HU6 7RX UK
| | - Emanuele Verrelli
- School of Mathematics & Physical Sciences, University of Hull Cottingham Road Hull HU6 7RX UK
| | - Fahad A Alharthi
- School of Mathematics & Physical Sciences, University of Hull Cottingham Road Hull HU6 7RX UK
- Department of Chemistry, College of Science, King Saud University P.O. Box 2455 Riyadh 11451 Saudi Arabia
| | - Stephen M Kelly
- School of Mathematics & Physical Sciences, University of Hull Cottingham Road Hull HU6 7RX UK
| | - Mary O'Neill
- School of Science & Technology, Nottingham Trent University 50 Shakespeare Street Nottingham NG1 3LL UK
| | - Neil T Kemp
- School of Mathematics & Physical Sciences, University of Hull Cottingham Road Hull HU6 7RX UK
| | - Stuart P Kitney
- Polar OLED, University of Hull Cottingham Road Hull HU6 7RX UK
| | - Khue T Lai
- Electronic Systems Design Centre, Energy Safety Research Institute, College of Engineering, Swansea University Bay Campus Swansea SA1 8EN UK
| | - Georg H Mehl
- School of Mathematics & Physical Sciences, University of Hull Cottingham Road Hull HU6 7RX UK
| | - Thomas Anthopoulos
- Centre for Plastic Electronics & Department of Physics, Blackett Laboratory, Imperial College London SW7 2BW UK
- Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST) Thuwal 23955-6900 Saudi Arabia
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25
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Parsouzi Z, Babakhanova G, Rajabi M, Saha R, Gyawali P, Turiv T, Wang H, Baldwin AR, Welch C, Mehl GH, Gleeson JT, Jakli A, Lavrentovich OD, Sprunt S. Pretransitional behavior of viscoelastic parameters at the nematic to twist-bend nematic phase transition in flexible n-mers. Phys Chem Chem Phys 2019; 21:13078-13089. [DOI: 10.1039/c9cp00984a] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
We report dynamic light scattering measurements of the orientational (Frank) elastic constants and associated viscosities among a homologous series of a liquid crystalline dimer, trimer, and tetramer exhibiting a uniaxial nematic (N) to twist-bend nematic (NTB) phase transition.
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Affiliation(s)
| | - Greta Babakhanova
- Advanced Materials and Liquid Crystal Institute
- Kent State University
- Kent
- USA
- Chemical Physics Interdisciplinary Program
| | | | - Rony Saha
- Department of Physics
- Kent State University
- Kent
- USA
| | | | - Taras Turiv
- Advanced Materials and Liquid Crystal Institute
- Kent State University
- Kent
- USA
- Chemical Physics Interdisciplinary Program
| | - Hao Wang
- Advanced Materials and Liquid Crystal Institute
- Kent State University
- Kent
- USA
- Chemical Physics Interdisciplinary Program
| | | | - Chris Welch
- Department of Chemistry
- University of Hull
- Hull
- UK
| | | | | | - Antal Jakli
- Department of Physics
- Kent State University
- Kent
- USA
- Advanced Materials and Liquid Crystal Institute
| | - Oleg D. Lavrentovich
- Department of Physics
- Kent State University
- Kent
- USA
- Advanced Materials and Liquid Crystal Institute
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26
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Fells JAJ, Wang X, Elston SJ, Welch C, Mehl GH, Booth MJ, Morris SM. Flexoelectro-optic liquid crystal analog phase-only modulator with a 2π range and 1 kHz switching. Opt Lett 2018; 43:4362-4365. [PMID: 30211871 DOI: 10.1364/ol.43.004362] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 07/26/2018] [Indexed: 06/08/2023]
Abstract
We present a flexoelectro-optic liquid crystal (LC) analog phase modulator with >2π phase range at a 1 kHz switching frequency. The chiral nematic LC mixture consists of the bimesogen CBC7CB with chiral dopant R5011, aligned in the uniform lying helix mode. The mixture exhibits >±π/4 rotation of the optic axis for a drive voltage of ±21.5 V (E=±4.5 V μm-1). The rotation of the optic axis is converted into a phase modulation with the aid of a reflective device configuration incorporating a ∼5 μm LC cell, a polarizer, two quarter-wave plates, and a mirror. The residual amplitude modulation is found to be <23%. This flexoelectro-optic phase modulator combination has the potential to enable analog spatial light modulators with very fast frame rates suitable for a range of applications.
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27
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Krzyżewska K, Jaroch T, Maranda-Niedbała A, Pociecha D, Górecka E, Ahmed Z, Welch C, Mehl GH, Proń A, Nowakowski R. Supramolecular organization of liquid-crystal dimers - bis-cyanobiphenyl alkanes on HOPG by scanning tunneling microscopy. Nanoscale 2018; 10:16201-16210. [PMID: 30123918 DOI: 10.1039/c8nr02069h] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
2D supramolecular organization of a series of six cyanobiphenyls bimesogens deposited on highly oriented pyrolytic graphite (HOPG) is studied by scanning tunneling microscopy (STM). The adsorbates are 1,ω-bis(4-cyanobiphenyl-4'-yl)alkanes (CBnCB) with different lengths of their flexible alkyl spacer (containing from 7 to 12 methylene groups). Microscopic investigations at the molecular resolution allow for detailed analysis of the effect of the alkyl spacer length on the type and the extent of the resulting 2D organization. It was demonstrated that bimesogens with shorter spacers (7 and 8 methylene units) organize in a similar manner characterized by the formation of two types of differently ordered monolayers: dense packed, wherein the molecules are oriented in one direction and ordered into parallel rows (layer structure), or less densely packed where they are organized into a chiral windmill-like structure. For derivatives with longer spacers (ranging from 9 to 12 methylene units) the additional effect of parity of carbon atoms in the spacer (even versus odd) is observed. In this range of the spacer lengths even membered bimesogens are also organized in a typical layer structure. However, odd-membered dimers exhibit a much more complex 2D supramolecular organization with a larger unit cell and a helical arrangement of the molecules. Careful comparison of this structure with the 3D structural data derived from the X-ray diffraction investigations of single crystals indicates that for these bimesogens a clear correlation exists between the observed complex 2D supramolecular organization in the monolayer and the organization in one of the crystallographic planes of the 3D nematic twist-bent phase.
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Affiliation(s)
- Klaudyna Krzyżewska
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warsaw 01-224, Poland.
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28
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Iadlovska OS, Maxwell GR, Babakhanova G, Mehl GH, Welch C, Shiyanovskii SV, Lavrentovich OD. Tuning selective reflection of light by surface anchoring in cholesteric cells with oblique helicoidal structures. Opt Lett 2018; 43:1850-1853. [PMID: 29652381 DOI: 10.1364/ol.43.001850] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Accepted: 03/06/2018] [Indexed: 06/08/2023]
Abstract
Selective reflection of light by oblique helicoidal cholesteric (ChOH) can be tuned in a very broad spectral range by an applied electric field. In this Letter, we demonstrate that the peak wavelength of the selective reflection can be controlled by the surface alignment of the director in sandwich cells. The peak wavelength is blue-shifted when the surface alignment is perpendicular to the bounding plates and red-shifted when it is planar. The effect is explained by the electric field redistribution within the cell caused by a spatially varying heliconical ChOH structure. The observed phenomenon can be used in sensing applications.
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29
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Stevenson WD, Ahmed Z, Zeng XB, Welch C, Ungar G, Mehl GH. Molecular organization in the twist-bend nematic phase by resonant X-ray scattering at the Se K-edge and by SAXS, WAXS and GIXRD. Phys Chem Chem Phys 2018; 19:13449-13454. [PMID: 28513674 DOI: 10.1039/c7cp01404j] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using a magnetically aligned liquid crystal mixture containing a novel Se-labelled dimer and the difluoroterphenyl dimer DTC5C7, the twist-bend nematic phase (Ntb) was studied by the resonant scattering of hard X-rays and by conventional small and wide-angle X-ray scattering (SAXS, WAXS). Resonant diffraction spots indicated a helix with a 9-12 nm pitch in the Ntb phase and an unprecedentedly high helix orientation. This enabled deconvolution of global and local order parameters. These findings, combined with the simultaneously recorded resonant and non-resonant SAXS and WAXS data, allowed us to construct a locally layered molecular model of the Ntb phase, where the average twisted conformation of each molecule was idealised as a helical segment, matching the local heliconical director field. The dimers were found to be less bent in the Ntb phase than in their minimum energy conformation, and straightening further with increasing temperature. It is proposed that on further heating their low bend angle allows the transition to the normal nematic phase, where the molecules can freely move longitudinally, without the need to perform screw-like motion as in the Ntb phase. At the low-temperature end, the increasing molecular twist becomes unsustainable, leading to a transition to a smectic phase, where no twist is required.
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Affiliation(s)
- W D Stevenson
- Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK.
| | - Z Ahmed
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - X B Zeng
- Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK.
| | - C Welch
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - G Ungar
- Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK. and Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
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30
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Stevenson WD, Zou HX, Zeng XB, Welch C, Ungar G, Mehl GH. Dynamic calorimetry and XRD studies of the nematic and twist-bend nematic phase transitions in a series of dimers with increasing spacer length. Phys Chem Chem Phys 2018; 20:25268-25274. [DOI: 10.1039/c8cp05744c] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A modulated DSC study of bent dimesogens with (CH2)n spacers n = 5–11 showed that the enthalpy of the ordinary nematic is lowest for n = 11 due to the lowest C–C torsion energy needed to straighten the dimer, causing near disappearance of twist-bend-nematic to nematic transition enthalpy.
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Affiliation(s)
- Warren D. Stevenson
- Department of Physics
- Zhejiang Sci-Tech University
- Hangzhou 310018
- China
- Department of Materials Science and Engineering
| | - Heng-xing Zou
- Department of Physics
- Zhejiang Sci-Tech University
- Hangzhou 310018
- China
| | - Xiang-bing Zeng
- Department of Materials Science and Engineering
- University of Sheffield
- Sheffield S1 3JD
- UK
| | | | - Goran Ungar
- Department of Physics
- Zhejiang Sci-Tech University
- Hangzhou 310018
- China
- Department of Materials Science and Engineering
| | - Georg H. Mehl
- Department of Chemistry
- University of Hull
- Hull HU6 7RX
- UK
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31
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Panov VP, Sreenilayam SP, Panarin YP, Vij JK, Welch CJ, Mehl GH. Characterization of the Submicrometer Hierarchy Levels in the Twist-Bend Nematic Phase with Nanometric Helices via Photopolymerization. Explanation for the Sign Reversal in the Polar Response. Nano Lett 2017; 17:7515-7519. [PMID: 29136474 DOI: 10.1021/acs.nanolett.7b03441] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Photopolymerization of a reactive mesogen mixed with a mesogenic dimer, shown to exhibit the twist-bend nematic phase (NTB), reveals the complex structure of the self-deformation patterns observed in planar cells. The polymerized reactive mesogen retains the structure formed by liquid crystalline molecules in the twist bend phase, thus enabling its observation by scanning electron microscopy (SEM). Hierarchical ordering scales ranging from tens of nanometers to micrometers are imaged in detail. Submicron features, anticipated from earlier X-ray experiments, are visualized directly. In the self-deformation stripes formed in the NTB phase, the average director field is found tilted in the cell plane by an angle of up to 45° from the cell rubbing direction. This tilt explains the sign inversion being observed in the electro-optical studies.
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Affiliation(s)
- Vitaly P Panov
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin , Dublin 2, Ireland
| | - Sithara P Sreenilayam
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin , Dublin 2, Ireland
| | - Yuri P Panarin
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin , Dublin 2, Ireland
- School of Electrical and Electronic Engineering, Dublin Institute of Technology , Dublin 8, Ireland
| | - Jagdish K Vij
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin , Dublin 2, Ireland
| | - Chris J Welch
- Department of Chemistry, University of Hull , Hull, HU6 7RX, U.K
| | - Georg H Mehl
- Department of Chemistry, University of Hull , Hull, HU6 7RX, U.K
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32
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Parsouzi Z, Pardaev SA, Welch C, Ahmed Z, Mehl GH, Baldwin AR, Gleeson JT, Lavrentovich OD, Allender DW, Selinger JV, Jakli A, Sprunt S. Light scattering study of the "pseudo-layer" compression elastic constant in a twist-bend nematic liquid crystal. Phys Chem Chem Phys 2016; 18:31645-31652. [PMID: 27834978 DOI: 10.1039/c6cp06292j] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic liquid crystalline (LC) dimers, features a nanometer-scale, heliconical rotation of the average molecular long axis (director) with equally probable left- and right-handed domains. On meso to macroscopic scales, the TB phase may be considered as a stack of equivalent slabs or "pseudo-layers", each one helical pitch in thickness. The long wavelength fluctuation modes should then be analogous to those of a smectic-A phase, and in particular the hydrodynamic mode combining "layer" compression and bending ought to be characterized by an effective layer compression elastic constant Beff and average director splay constant K. The magnitude of K is expected to be similar to the splay constant of an ordinary nematic LC, but due to the absence of a true mass density wave, Beff could differ substantially from the typical value of ∼106 Pa in a conventional smectic-A. Here we report the results of a dynamic light scattering study, which confirms the "pseudo-layer" structure of the TB phase with Beff in the range 103-104 Pa. We show additionally that the temperature dependence of Beff at the TB to nematic transition is accurately described by a coarse-grained free energy density, which is based on a Landau-deGennes expansion in terms of a heli-polar order parameter that characterizes the TB state and is linearly coupled to bend distortion of the director.
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Affiliation(s)
- Z Parsouzi
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - Shokir A Pardaev
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - C Welch
- G. W. Gray Centre for Advanced Materials, Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - Z Ahmed
- G. W. Gray Centre for Advanced Materials, Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - G H Mehl
- G. W. Gray Centre for Advanced Materials, Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - A R Baldwin
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - J T Gleeson
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - O D Lavrentovich
- Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - D W Allender
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - J V Selinger
- Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - A Jakli
- Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - S Sprunt
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
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Salili SM, Tamba MG, Sprunt SN, Welch C, Mehl GH, Jákli A, Gleeson JT. Anomalous Increase in Nematic-Isotropic Transition Temperature in Dimer Molecules Induced by a Magnetic Field. Phys Rev Lett 2016; 116:217801. [PMID: 27284674 DOI: 10.1103/physrevlett.116.217801] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Indexed: 06/06/2023]
Abstract
We have determined the nematic-isotropic transition temperature as a function of an applied magnetic field in three different thermotropic liquid crystalline dimers. These molecules are comprised of two rigid calamitic moieties joined end to end by flexible spacers with odd numbers of methylene groups. They show an unprecedented magnetic field enhancement of nematic order in that the transition temperature is increased by up to 15 K when subjected to a 22 T magnetic field. The increase is conjectured to be caused by a magnetic-field-induced decrease of the average bend angle in the aliphatic spacers connecting the rigid mesogenic units of the dimers.
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Affiliation(s)
- S M Salili
- Chemical Physics Interdisciplinary Program & Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - M G Tamba
- Department of Nonlinear Phenomena, Institute for Experimental Physics, Otto von Guericke University Magdeburg, Magdeburg 39106, Germany
| | - S N Sprunt
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - C Welch
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - A Jákli
- Chemical Physics Interdisciplinary Program & Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - J T Gleeson
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
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34
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Pardaev SA, Shamid SM, Tamba MG, Welch C, Mehl GH, Gleeson JT, Allender DW, Selinger JV, Ellman B, Jakli A, Sprunt S. Second harmonic light scattering induced by defects in the twist-bend nematic phase of liquid crystal dimers. Soft Matter 2016; 12:4472-4482. [PMID: 27089236 DOI: 10.1039/c6sm00585c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The nematic twist-bend (NTB) phase, exhibited by certain thermotropic liquid crystalline (LC) dimers, represents a new orientationally ordered mesophase - the first distinct nematic variant discovered in many years. The NTB phase is distinguished by a heliconical winding of the average molecular long axis (director) with a remarkably short (nanoscale) pitch and, in systems of achiral dimers, with an equal probability to form right- and left-handed domains. The NTB structure thus provides another fascinating example of spontaneous chiral symmetry breaking in nature. The order parameter driving the formation of the heliconical state has been theoretically conjectured to be a polarization field, deriving from the bent conformation of the dimers, that rotates helically with the same nanoscale pitch as the director field. It therefore presents a significant challenge for experimental detection. Here we report a second harmonic light scattering (SHLS) study on two achiral, NTB-forming LCs, which is sensitive to the polarization field due to micron-scale distortion of the helical structure associated with naturally-occurring textural defects. These defects are parabolic focal conics of smectic-like "pseudo-layers", defined by planes of equivalent phase in a coarse-grained description of the NTB state. Our SHLS data are explained by a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a linear coupling between the two.
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Affiliation(s)
- Shokir A Pardaev
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - S M Shamid
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - M G Tamba
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - C Welch
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - J T Gleeson
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - D W Allender
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - J V Selinger
- Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - B Ellman
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - A Jakli
- Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - S Sprunt
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
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35
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Kurochkin O, Murugesan YK, Bennett TP, D'Alessandro G, Reznikov Y, Tang BJ, Mehl GH, Kaczmarek M. Thermal optical non-linearity of nematic mesophase enhanced by gold nanoparticles--an experimental and numerical investigation. Phys Chem Chem Phys 2016; 18:11503-12. [PMID: 27063912 DOI: 10.1039/c6cp00116e] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this work the mechanisms leading to the enhancement of optical nonlinearity of nematic liquid crystalline material through localized heating by doping the liquid crystals (LCs) with gold nanoparticles (GNPs) are investigated. We present some experimental and theoretical results on the effect of voltage and nanoparticle concentration on the nonlinear response of GNP-LC suspensions. The optical nonlinearity of these systems is characterized by diffraction measurements and the second order nonlinear refractive index, n2, is used to compare systems with different configurations and operating conditions. A theoretical model based on heat diffusion that takes into account the intensity and finite size of the incident beam, the nanoparticle concentration dependent absorbance of GNP doped LC systems and the presence of bounding substrates is developed and validated. We use the model to discuss the possibilities of further enhancing the optical nonlinearity.
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Affiliation(s)
- O Kurochkin
- Institute of Physics of National Academy of Sciences of Ukraine, Kyiv 03028, Ukraine
| | - Y K Murugesan
- School of Mathematics, University of Southampton, Southampton, SO17 1BJ, UK
| | - T P Bennett
- School of Mathematics, University of Southampton, Southampton, SO17 1BJ, UK
| | - G D'Alessandro
- School of Mathematics, University of Southampton, Southampton, SO17 1BJ, UK
| | - Y Reznikov
- Institute of Physics of National Academy of Sciences of Ukraine, Kyiv 03028, Ukraine
| | - B J Tang
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK
| | - M Kaczmarek
- School of Physics, University of Southampton, Southampton, SO17 1BJ, UK.
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36
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Yen MH, Chaiprapa J, Zeng X, Liu Y, Cseh L, Mehl GH, Ungar G. Added Alkane Allows Thermal Thinning of Supramolecular Columns by Forming Superlattice—An X-ray and Neutron Study. J Am Chem Soc 2016; 138:5757-60. [DOI: 10.1021/jacs.6b01172] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ming-Huei Yen
- Department
of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, U.K
| | - Jitrin Chaiprapa
- Department
of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, U.K
| | - Xiangbing Zeng
- Department
of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, U.K
| | - Yongsong Liu
- Department
of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China
| | - Liliana Cseh
- Department
of Chemistry, University of Hull, Hull HU6 7RX, U.K
- Institute of Chemistry, Timisoara of Romanian Academy, Timisoara 300223, Romania
| | - Georg H. Mehl
- Department
of Chemistry, University of Hull, Hull HU6 7RX, U.K
| | - Goran Ungar
- Department
of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, U.K
- Department
of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China
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37
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Abstract
The phase behaviour of mixtures between two symmetric dimers, CBC9CB and the ether-linked analogue CBOC9OCB was investigated by Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) studies. The dimeric constituents are fully miscible and the construction of a temperature-composition phase diagram reveals a surprising amplification of the stability of the Nx phase in compositions of up to 37 wt% of CBOC9OCB in CBC9CB. The origin for this enhancement of stability is discussed and an explanation based on chiral recognition is developed.
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Affiliation(s)
- E Ramou
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK.
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38
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Cseh L, Mang X, Zeng X, Liu F, Mehl GH, Ungar G, Siligardi G. Helically Twisted Chiral Arrays of Gold Nanoparticles Coated with a Cholesterol Mesogen. J Am Chem Soc 2015; 137:12736-9. [DOI: 10.1021/jacs.5b05059] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Liliana Cseh
- Department
of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - Xiaobin Mang
- Department
of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom
| | - Xiangbing Zeng
- Department
of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom
| | - Feng Liu
- Department
of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom
- State
Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, 710049, PR China
| | - Georg H. Mehl
- Department
of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - Goran Ungar
- Department
of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, PR China
- Department
of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom
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Hoffmann A, Vanakaras AG, Kohlmeier A, Mehl GH, Photinos DJ. On the structure of the Nx phase of symmetric dimers: inferences from NMR. Soft Matter 2015; 11:850-855. [PMID: 25571939 DOI: 10.1039/c4sm02480j] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
NMR measurements on a selectively deuterated liquid crystal dimer CB-C9-CB, exhibiting two nematic phases, show that the molecules in the lower temperature nematic phase, N(X), experience a chiral environment and are ordered about a uniformly oriented director throughout the macroscopic sample. The results are contrasted with previous interpretations that suggested a twist-bend spatial variation of the director. A structural picture is proposed wherein the molecules are packed into highly correlated chiral assemblies.
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Affiliation(s)
- Anke Hoffmann
- Department of Inorganic and Analytical Chemistry, University of Freiburg, Albertstr. 21, 79104 Freiburg, Germany
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40
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Rutkevičius M, Mehl GH, Petkov JT, Stoyanov SD, Paunov VN. Fabrication of salt–hydrogel marbles and hollow-shell microcapsules by an aerosol gelation technique. J Mater Chem B 2015; 3:82-89. [DOI: 10.1039/c4tb01443j] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We discovered a way to make hydrogel marbles with hydrophilic particles by rolling gelled aerosol droplets in a bed of salt microcrystals which after sieving and drying of the hydrogel cores yielded hollow-shell salt microcapsules.
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Affiliation(s)
| | - Georg H. Mehl
- Department of Chemistry
- University of Hull
- Hull HU6 7RX
- UK
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41
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Gao M, Kim YK, Zhang C, Borshch V, Zhou S, Park HS, Jákli A, Lavrentovich OD, Tamba MG, Kohlmeier A, Mehl GH, Weissflog W, Studer D, Zuber B, Gnägi H, Lin F. Direct observation of liquid crystals using cryo-TEM: specimen preparation and low-dose imaging. Microsc Res Tech 2014; 77:754-72. [PMID: 25045045 DOI: 10.1002/jemt.22397] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2014] [Revised: 05/10/2014] [Accepted: 06/23/2014] [Indexed: 11/07/2022]
Abstract
Liquid crystals (LCs) represent a challenging group of materials for direct transmission electron microscopy (TEM) studies due to the complications in specimen preparation and the severe radiation damage. In this paper, we summarize a series of specimen preparation methods, including thin film and cryo-sectioning approaches, as a comprehensive toolset enabling high-resolution direct cryo-TEM observation of a broad range of LCs. We also present comparative analysis using cryo-TEM and replica freeze-fracture TEM on both thermotropic and lyotropic LCs. In addition to the revisits of previous practices, some new concepts are introduced, e.g., suspended thermotropic LC thin films, combined high-pressure freezing and cryo-sectioning of lyotropic LCs, and the complementary applications of direct TEM and indirect replica TEM techniques. The significance of subnanometer resolution cryo-TEM observation is demonstrated in a few important issues in LC studies, including providing direct evidences for the existence of nanoscale smectic domains in nematic bent-core thermotropic LCs, comprehensive understanding of the twist-bend nematic phase, and probing the packing of columnar aggregates in lyotropic chromonic LCs. Direct TEM observation opens ways to a variety of TEM techniques, suggesting that TEM (replica, cryo, and in situ techniques), in general, may be a promising part of the solution to the lack of effective structural probe at the molecular scale in LC studies.
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Affiliation(s)
- Min Gao
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio, 44242
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42
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Borshch V, Kim YK, Xiang J, Gao M, Jákli A, Panov VP, Vij JK, Imrie CT, Tamba MG, Mehl GH, Lavrentovich OD. Nematic twist-bend phase with nanoscale modulation of molecular orientation. Nat Commun 2014; 4:2635. [PMID: 24189583 PMCID: PMC3831290 DOI: 10.1038/ncomms3635] [Citation(s) in RCA: 283] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 09/18/2013] [Indexed: 11/12/2022] Open
Abstract
A state of matter in which molecules show a long-range orientational order and no positional order is called a nematic liquid crystal. The best known and most widely used (for example, in modern displays) is the uniaxial nematic, with the rod-like molecules aligned along a single axis, called the director. When the molecules are chiral, the director twists in space, drawing a right-angle helicoid and remaining perpendicular to the helix axis; the structure is called a chiral nematic. Here using transmission electron and optical microscopy, we experimentally demonstrate a new nematic order, formed by achiral molecules, in which the director follows an oblique helicoid, maintaining a constant oblique angle with the helix axis and experiencing twist and bend. The oblique helicoids have a nanoscale pitch. The new twist-bend nematic represents a structural link between the uniaxial nematic (no tilt) and a chiral nematic (helicoids with right-angle tilt). Theories predict the existence of a nematic liquid crystal phase with a local twist-bend structure, but no experimental proof is available over the past 40 years. Borshch et al. identify this phase for the first time in two different materials containing dimeric molecules.
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Affiliation(s)
- V Borshch
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA
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43
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Tamba MG, Yu CH, Tang BJ, Welch C, Kohlmeier A, Schubert CP, Mehl GH. The Design and Investigation of Nanocomposites Containing Dimeric Nematogens and Liquid Crystal Gold Nanoparticles with Plasmonic Properties Showing a Nematic-Nematic Phase Transition (N u-N x/N tb). Materials (Basel) 2014; 7:3494-3511. [PMID: 28788631 PMCID: PMC5453202 DOI: 10.3390/ma7053494] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Revised: 04/11/2014] [Accepted: 04/17/2014] [Indexed: 11/16/2022]
Abstract
The construction of liquid crystal compositions consisting of the dimeric liquid crystal, CB_C9_CB (cyanobiphenyl dimer = 1'',9''-bis(4-cyanobiphenyl-4'-yl)nonane), and the range of nematic systems is explored. The materials include a laterally functionalized monomer, which was used to construct a phase diagram with CB_C9_CB, as well as one laterally linked dimer liquid crystal material and two liquid crystal gold nanoparticle (LC-Au-NPs) systems. For the Au-NP-LCs, the NP diameters were varied between ~3.3 nm and 10 nm. Stable mixtures that exhibit a nematic-nematic phase transition are reported and were investigated by POM (polarizing optical microscopy), DSC (differential scanning calorimetry) and X-ray diffraction studies.
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Affiliation(s)
| | - Chih Hao Yu
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK.
| | - Bai Jia Tang
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK.
| | | | | | | | - Georg H Mehl
- Department of Chemistry, University of Hull, Hull, HU6 7RX, UK.
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Kim YK, Senyuk B, Shin ST, Kohlmeier A, Mehl GH, Lavrentovich OD. Surface alignment, anchoring transitions, optical properties, and topological defects in the thermotropic nematic phase of organo-siloxane tetrapodes. Soft Matter 2014; 10:500-509. [PMID: 24651889 DOI: 10.1039/c3sm52249k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We perform optical, surface anchoring, and textural studies of an organo-siloxane "tetrapode" material in the broad temperature range of the nematic phase. The optical, structural, and topological features are compatible with the uniaxial nematic order rather than with the biaxial nematic order, in the entire nematic temperature range -25 °C < T < 46 °C studied. For homeotropic alignment, the material experiences surface anchoring transition, but the director can be realigned into an optically uniaxial texture by applying a sufficiently strong electric field. The topological features of textures in cylindrical capillaries, in spherical droplets and around colloidal inclusions are consistent with the uniaxial character of the long-range nematic order. In particular, we observe isolated surface point defects - boojums and bulk point defects - hedgehogs that can exist only in the uniaxial nematic liquid crystal.
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Affiliation(s)
- Young-Ki Kim
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent, OH 44242, USA.
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Dintinger J, Tang BJ, Zeng X, Liu F, Kienzler T, Mehl GH, Ungar G, Rockstuhl C, Scharf T. A self-organized anisotropic liquid-crystal plasmonic metamaterial. Adv Mater 2013; 25:1999-2004. [PMID: 23401232 DOI: 10.1002/adma.201203965] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 12/28/2012] [Indexed: 05/24/2023]
Abstract
A composite material that leads to self organization of mesogen-coated gold nanospheres is synthesized and shows enhanced anisotropic optical properties due to synergistic effects of the mesogens intrinsic birefringence and its ability to drive the self-assembly process into highly anisotropic architectures with densely packed nanospheres. Such nanoengineered matter sustains a response beyond that achievable by its individual constituents, i.e., a metamaterial.
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Affiliation(s)
- José Dintinger
- Optics & Photonics Technology Laboratory, Ecole Polytechnique Fédérale de Lausanne, Neuchâtel, Switzerland
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Polineni S, Figueirinhas JL, Cruz C, Wilson DA, Mehl GH. Capacitance and optical studies of elastic and dielectric properties in an organosiloxane tetrapode exhibiting a N(B) phase. J Chem Phys 2013; 138:124904. [PMID: 23556748 DOI: 10.1063/1.4795582] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Biaxial (N(B)) and uniaxial nematic (N(U)) phase behavior was detected and confirmed for an organosiloxane tetrapode material using capacitance and birefringence measurements. Elastic constants, permittivities at two distinct low frequencies, and birefringencies were determined as a function of temperature over both the N(U) and the N(B) phase ranges. The N(U)-N(B) transition is clearly observed in the birefringencies and conoscopy data. A temperature dependent cross-over frequency is also detected in this material for the permittivities, allowing the electrical switching of both planar and homeotropic aligned samples.
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Affiliation(s)
- S Polineni
- IST-Technical University of Lisbon, Dept. de Física, Av. Rovisco Pais, P-1049-001 Lisboa, Portugal
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Halls JE, Bourne RW, Wright KJ, Partington LI, Tamba MG, Zhou Y, Ramakrishnappa T, Mehl GH, Kelly SM, Wadhawan JD. Electrochemistry of organometallic lyotropic chromonic liquid crystals. Electrochem commun 2012. [DOI: 10.1016/j.elecom.2012.02.032] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
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Lysenko D, Ouskova E, Ksondzyk S, Reshetnyak V, Cseh L, Mehl GH, Reznikov Y. Light-induced changes of the refractive indices in a colloid of gold nanoparticles in a nematic liquid crystal. Eur Phys J E Soft Matter 2012; 35:33. [PMID: 22592815 DOI: 10.1140/epje/i2012-12033-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2012] [Revised: 04/24/2012] [Accepted: 04/24/2012] [Indexed: 05/31/2023]
Abstract
It was shown that irradiation of a nematic liquid crystal doped with metal nanoparticles in the visible near the plasmon resonance band led to strong thermal changes of the refractive indices. The effect was studied by recording of dynamic optical gratings in the colloid. Nanoparticles "worked" as effective nano-heaters in a matrix causing the order parameter decrease around the particles. A large nonlinearity parameter (n (2) ≈ 10(-2) cm(2)/kW and fast response (≈ 0.7 ms), with no detectable particles' aggregation and excellent photo- thermo-stability make these colloids potentially attractive nonlinear optical media. Application of a dynamic holography technique allowed measuring the coefficients of thermal conductivity of the liquid crystal along the director k (||) = (0.4 ± 0.02) W m(-1)K(-1) and perpendicular to the director k (⊥) = (0.2 ± 0.01) W m(-1)K(-1).
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Affiliation(s)
- D Lysenko
- Institute of Physics, National Academy of Sciences of Ukraine, Pr. Nauki 46, 03028 Kyiv, Ukraine
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Yu CH, Schubert CPJ, Welch C, Tang BJ, Tamba MG, Mehl GH. Design, Synthesis, and Characterization of Mesogenic Amine-Capped Nematic Gold Nanoparticles with Surface-Enhanced Plasmonic Resonances. J Am Chem Soc 2012; 134:5076-9. [PMID: 22390286 DOI: 10.1021/ja300492d] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Chih H. Yu
- Department of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, United Kingdom
| | | | - Chris Welch
- Department of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, United Kingdom
| | - Bai J. Tang
- Department of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, United Kingdom
| | - M.-Gabriela Tamba
- Department of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, United Kingdom
| | - Georg H. Mehl
- Department of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, United Kingdom
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Merkel K, Nagaraj M, Kocot A, Kohlmeier A, Mehl GH, Vij JK. Biaxial order and a rotation of the minor director in the nematic phase of an organo-siloxane tetrapode by the electric field. J Chem Phys 2012; 136:094513. [PMID: 22401458 DOI: 10.1063/1.3690108] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Biaxiality in the nematic phase for a liquid crystalline tetrapode made up of organo-siloxanes mesogens is investigated using polarized infrared spectroscopy. An ordering of the minor director for the homeotropically aligned sample is found to depend on the amplitude of the in-plane electric field. On increasing the in-plane electric field, the minor director, lying initially along the rubbing direction, rotates to the direction of the applied field. The scalar order parameters of the second rank tensor are found to depend significantly on the strength of the electric field. A most significant increase is found in the nematic order parameter and in the parameter that characterizes the phase biaxiality.
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Affiliation(s)
- K Merkel
- Central Mining Institute, Plac Gwarkow 1, Katowice, Poland
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