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Colloidal and fumed particles in nematic liquid crystals: Self-assembly, confinement and implications on rheology. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.116241] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Kumar S, Singh G, Thareja P. Surface chemistry driven dynamic rheology, microstructure of fumed and colloidal silica particles in nematic liquid crystals. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.113623] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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3
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Selevou A, Papamokos G, Yildirim T, Duran H, Steinhart M, Floudas G. Eutectic liquid crystal mixture E7 in nanoporous alumina. Effects of confinement on the thermal and concentration fluctuations. RSC Adv 2019; 9:37846-37857. [PMID: 35541799 PMCID: PMC9075738 DOI: 10.1039/c9ra08806g] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Accepted: 11/11/2019] [Indexed: 11/21/2022] Open
Abstract
The eutectic mixture of liquid crystals E7 is studied in confinement by means of thermal and dielectric measurements. The uniform 1-D confinement provided by self-ordered nanoporous alumina leads to a decrease in the nematic to isotropic transition temperature due to interaction with the pore surface, e.g. surface anchoring. The prevalence of certain dynamic modes of relaxation is found to depend on the surface properties of the confining pores. The dynamics (i.e., relaxation times) were found to accelerate with increasing confinement, resulting in a decreasing glass temperature, independent of surface treatment. From the pre- and meta-transitional dependence of the dielectric permittivity on temperature we are able to deduce a weakening effect of confinement on the nematic to isotropic (N/I) transition which allows the determination of a critical pore diameter (in the range from 11 nm to 23 nm) below which the transition becomes continuous. Comparison of the N/I transition of E7 to those of its constituent liquid crystals reveals a significantly weaker transition occurring over a widened temperature range. This suggest the importance of concentration fluctuations in rounding first order phase transitions that are triggered by the different length scales and ranges of nematic stability in E7. The results have an impact beyond the present case and for several soft materials (e.g. oligomers used as OLEDs, polymers, colloids) as it demonstrates the importance of concentration fluctuations in addition to thermal fluctuation on the strength of phase transitions.
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Affiliation(s)
- Aristoula Selevou
- Department of Physics, University of Ioannina P. O. Box 1186 451 10 Ioannina Greece
| | - George Papamokos
- Department of Physics, University of Ioannina P. O. Box 1186 451 10 Ioannina Greece
| | - Tolga Yildirim
- Department of Materials Science & Nanotechnology Engineering, TOBB University of Economics and Technology Söğütözü Cad. 43 Ankara 06560 Turkey
| | - Hatice Duran
- Department of Materials Science & Nanotechnology Engineering, TOBB University of Economics and Technology Söğütözü Cad. 43 Ankara 06560 Turkey
| | - Martin Steinhart
- Institut für Chemie Neuer Materialien, Universität Osnabrück D-49069 Osnabrück Germany
| | - George Floudas
- Department of Physics, University of Ioannina P. O. Box 1186 451 10 Ioannina Greece
- University Research Center of Ioannina (URCI), Institute of Materials Science and Computing Ioannina Greece
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Correlation between dielectric properties and phase transitions of 8CB/Sn 2 P 2 S 6 liquid crystal nanocolloids. J Mol Liq 2017. [DOI: 10.1016/j.molliq.2017.02.060] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Kumar P, Jaggi C, Sharma V, Raina KK. Advancements of vertically aligned liquid crystal displays. Micron 2016; 81:34-47. [PMID: 26800482 DOI: 10.1016/j.micron.2015.11.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2015] [Accepted: 11/04/2015] [Indexed: 11/28/2022]
Abstract
This review describes the recent advancements in the field of the vertical aligned (VA) liquid crystal displays. The process and formation of different vertical alignment modes such as conventional VA, patterned VA, multi-domain VA, and polymer stabilised VA etc are widely discussed. Vertical alignment of liquid crystal due to nano particle dispersion in LC host, bifunctional PR-SAM formed by silane coupling reaction to oxide surfaces, azo dye etc., are also highlighted and discussed. Overall, the article highlights the advances in the research of vertical aligned liquid crystal in terms of their scientific and technological aspects.
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Affiliation(s)
- Pankaj Kumar
- School of Applied Science, Chitkara University, Jansla, Rajpura, Patiala, 140401 Punjab, India; Chitkara University Research and Innovation Network, Chitkara University, Jansla, Rajpura, Patiala, 140401 Punjab, India.
| | - Chinky Jaggi
- School of Applied Science, Chitkara University, Jansla, Rajpura, Patiala, 140401 Punjab, India
| | - Vandna Sharma
- School of Applied Science, Chitkara University, Jansla, Rajpura, Patiala, 140401 Punjab, India
| | - Kuldeep Kumar Raina
- DIT University, Mussourie-Diversion Road, Dehradun, Uttarakhand 248009, India.
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Całus S, Borowik L, Kityk AV, Eich M, Busch M, Huber P. Thermotropic interface and core relaxation dynamics of liquid crystals in silica glass nanochannels: a dielectric spectroscopy study. Phys Chem Chem Phys 2015; 17:22115-24. [PMID: 26255586 DOI: 10.1039/c5cp03039k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report dielectric relaxation spectroscopy experiments on two rod-like liquid crystals of the cyanobiphenyl family (5CB and 6CB) confined in tubular nanochannels with 7 nm radius and 340 micrometer length in a monolithic, mesoporous silica membrane. The measurements were performed on composites for two distinct regimes of fractional filling: monolayer coverage at the pore walls and complete filling of the pores. For the layer coverage a slow surface relaxation dominates the dielectric properties. For the entirely filled channels the dielectric spectra are governed by two thermally-activated relaxation processes with considerably different relaxation rates: a slow relaxation in the interface layer next to the channel walls and a fast relaxation in the core region of the channel filling. The strengths and characteristic frequencies of both relaxation processes have been extracted and analysed as a function of temperature. Whereas the temperature dependence of the static capacitance reflects the effective (average) molecular ordering over the pore volume and is well described within a Landau-de Gennes theory, the extracted relaxation strengths of the slow and fast relaxation processes provide an access to distinct local molecular ordering mechanisms. The order parameter in the core region exhibits a bulk-like behaviour with a strong increase in the nematic ordering just below the paranematic-to-nematic transition temperature TPN and subsequent saturation during cooling. By contrast, the surface ordering evolves continuously with a kink near TPN. A comparison of the thermotropic behaviour of the monolayer with the complete filling reveals that the molecular order in the core region of the pore filling affects the order of the peripheral molecular layers at the wall.
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Affiliation(s)
- Sylwia Całus
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
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Lin Y, Douali R, Dubois F, Segovia-Mera A, Daoudi A. On the phase transitions of 8CB/Sn2P2S6 liquid crystal nanocolloids. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2015; 38:103. [PMID: 26410848 DOI: 10.1140/epje/i2015-15103-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Revised: 06/11/2015] [Accepted: 08/28/2015] [Indexed: 06/05/2023]
Abstract
Using differential scanning calorimetry measurements, the influence of Sn2P2S6 ferroelectric nanoparticles on the phase transition temperatures of the 8CB liquid crystal is studied. The spontaneous polarization, ionic and anchoring effects are discussed. For low concentration of dopant, the global effect leads to a decrease and an increase of the nematic-isotropic and the smectic A-nematic phase transition temperatures, respectively. For high concentrations, due to aggregates formation, the predominant anchoring effect induces a decrease of the both phase transition temperatures.
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Affiliation(s)
- Y Lin
- Unité de Dynamique et Structure des Matériaux Moléculaires (UDSMM), Université du Littoral Côte d'Opale (ULCO), 50, Rue Ferdinand Buisson, 62228, Calais Cedex, France.
| | - R Douali
- Unité de Dynamique et Structure des Matériaux Moléculaires (UDSMM), Université du Littoral Côte d'Opale (ULCO), 50, Rue Ferdinand Buisson, 62228, Calais Cedex, France
| | - F Dubois
- Unité de Dynamique et Structure des Matériaux Moléculaires (UDSMM), Université du Littoral Côte d'Opale (ULCO), 50, Rue Ferdinand Buisson, 62228, Calais Cedex, France
| | - A Segovia-Mera
- Unité de Dynamique et Structure des Matériaux Moléculaires (UDSMM), Université du Littoral Côte d'Opale (ULCO), 145, Avenue Maurice Schumann, 59140, Dunkerque, France
| | - A Daoudi
- Unité de Dynamique et Structure des Matériaux Moléculaires (UDSMM), Université du Littoral Côte d'Opale (ULCO), 145, Avenue Maurice Schumann, 59140, Dunkerque, France
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Pawsey AC, Clegg PS. Colloidal particles in blue phase liquid crystals. SOFT MATTER 2015; 11:3304-3312. [PMID: 25698218 DOI: 10.1039/c4sm02131b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We study the effect of disorder on the phase transitions of a system already dominated by defects. Micron-sized colloidal particles are dispersed chiral nematic liquid crystals which exhibit a blue phase (BP). The colloids are a source of disorder, disrupting the liquid crystal as the system is heated from the cholesteric to the isotropic phase through the blue phase. The colloids act as a preferential site for the growth of BPI from the cholesteric; in high chirality samples BPII also forms. In both BPI and BPII the colloids lead to localised melting to the isotropic, giving rise to faceted isotropic inclusions. This is in contrast to the behaviour of a cholesteric LC where colloids lead to system spanning defects.
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Affiliation(s)
- Anne C Pawsey
- SUPA, School of Physics and Astronomy, JCMB, Mayfield Road, Edinburgh, EH9 3JZ, UK.
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Całus S, Kityk AV, Eich M, Huber P. Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid. SOFT MATTER 2015; 11:3176-3187. [PMID: 25759093 DOI: 10.1039/c5sm00108k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report filling-fraction dependent dielectric spectroscopy measurements on the relaxation dynamics of the rod-like nematogen 7CB condensed in 13 nm silica nanochannels. In the film-condensed regime, a slow interface relaxation dominates the dielectric spectra, whereas from the capillary-condensed state up to complete filling an additional, fast relaxation in the core of the channels is found. The temperature-dependence of the static capacitance, representative of the averaged, collective molecular orientational ordering, indicates a continuous, paranematic-to-nematic (P-N) transition, in contrast to the discontinuous bulk behaviour. It is well described by a Landau-de-Gennes free energy model for a phase transition in cylindrical confinement. The large tensile pressure of 10 MPa in the capillary-condensed state, resulting from the Young-Laplace pressure at highly curved liquid menisci, quantitatively accounts for a downward-shift of the P-N transition and an increased molecular mobility in comparison to the unstretched liquid state of the complete filling. The strengths of the slow and fast relaxations provide local information on the orientational order: the thermotropic behaviour in the core region is bulk-like, i.e. it is characterized by an abrupt onset of the nematic order at the P-N transition. By contrast, the interface ordering exhibits a continuous evolution at the P-N transition. Thus, the phase behaviour of the entirely filled liquid crystal-silica nanocomposite can be quantitatively described by a linear superposition of these distinct nematic order contributions.
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Affiliation(s)
- Sylwia Całus
- Faculty of Electrical Engineering, Czestochowa University of Technology, Al. Armii Krajowej 17, 42-200 Czestochowa, Poland.
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Repnik R, Ranjkesh A, Simonka V, Ambrozic M, Bradac Z, Kralj S. Symmetry breaking in nematic liquid crystals: analogy with cosmology and magnetism. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:404201. [PMID: 24025777 DOI: 10.1088/0953-8984/25/40/404201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Universal behavior related to continuous symmetry breaking in nematic liquid crystals is studied using Brownian molecular dynamics. A three-dimensional lattice system of rod-like objects interacting via the Lebwohl-Lasher interaction is considered. We test the applicability of predictions originally derived in cosmology and magnetism. In the first part we focus on coarsening dynamics following the temperature driven isotropic-nematic phase transition for different quench rates. The behavior in the early coarsening regime supports predictions made originally by Kibble in cosmology. For fast enough quenches, symmetry breaking and causality give rise to a dense tangle of defects. When the degree of orientational ordering is large enough, well defined protodomains characterized by a single average domain length are formed. With time subcritical domains gradually vanish and supercritical domains grow with time, exhibiting a universal scaling law. In the second part of the paper we study the impact of random-field-type disorder on a range of ordering in the (symmetry broken) nematic phase. We demonstrate that short-range order is observed even for a minute concentration of impurities, giving rise to disorder in line with the Imry-Ma theorem prediction only for the appropriate history of systems.
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Affiliation(s)
- R Repnik
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroska 160, 2000 Maribor, Slovenia
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12
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Chang CW, Huang CY, Song HC. Initially twisted pi cell fabricated using liquid crystal-silica colloidal dispersions. OPTICS EXPRESS 2011; 19:13306-13311. [PMID: 21747485 DOI: 10.1364/oe.19.013306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We demonstrate an initially twisted pi cell fabricated by doping silica nanoparticles into the conventional pi cell. With AC high voltage, the director distortion of the liquid crystals (LCs) near the substrate surface creates a lifting force, which moves the silica nanoparticles toward the substrate surfaces. The accumulated silica nanoparticles on the substrate surfaces stabilize the LCs at the twisted pi state when the AC high voltage is turned off. The formed twisted pi state is permanent. The operation voltage and the response time of the initially twisted pi cell are less than those of the conventional pi cell.
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Affiliation(s)
- Che-Wei Chang
- Graduate Institute of Photonics, National Changhua University of Education, Changhua, Taiwan
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13
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Frunza S, Schönhals A, Frunza L, Beica T, Zgura I, Ganea P, Stoenescu D. Dynamics of cyanophenyl alkylbenzoate molecules in the bulk and in a surface layer adsorbed onto aerosil. Variation of the lengths of the alkyl chain. Chem Phys 2010. [DOI: 10.1016/j.chemphys.2010.04.031] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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14
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Huang CY, Huang YJ, Tseng YH. Dual-operation-mode liquid crystal lens. OPTICS EXPRESS 2009; 17:20860-20865. [PMID: 19997321 DOI: 10.1364/oe.17.020860] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We demonstrate a dual-operation-mode liquid crystal (LC) lens, which is fabricated with the silica nanoparticle-doped (SND) hybrid-aligned nematic (HAN) LC cell. With AC voltage, the cell behaves as a conventional LC lens. The response time of the SND HAN LC lens is faster than that of the conventional LC lens, which is fabricated using the pristine HAN LC cell. This is because that the doped silica nanoparticles may decrease the dielectric relaxation time constant of the cell. The addition of the silica nanoparticles also increases the viscosity of the LC host, suppresses the backflow motion of the LCs and then decreases the response time of the SND LC lens. With DC voltage, the electrophoretic motion of the doped silica nanoparticles and the agglomerate silica networks on the substrate surface cause the SND HAN LC cell to function as a bistable LC lens.
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Affiliation(s)
- Chi-Yen Huang
- Graduate Institute of Photonics, National Changhua University of Education, Changhua, Taiwan 500, Republic of China.
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15
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The influence of disorder on thermotropic nematic liquid crystals phase behavior. Int J Mol Sci 2009; 10:3971-4008. [PMID: 19865529 PMCID: PMC2769155 DOI: 10.3390/ijms10093971] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2009] [Revised: 08/07/2009] [Accepted: 08/14/2009] [Indexed: 11/23/2022] Open
Abstract
We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several open questions with respect to the impact of disorder on universal phase and structural behavior could be explored. Main advantages of liquid crystalline materials and different experimental realizations of random field-type disorder imposed on liquid crystal phases are described.
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Cordoyiannis G, Zidansek A, Lahajnar G, Kutnjak Z, Amenitsch H, Nounesis G, Kralj S. Influence of confinement in controlled-pore glass on the layer spacing of smectic- a liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:051703. [PMID: 19518470 DOI: 10.1103/physreve.79.051703] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2008] [Indexed: 05/27/2023]
Abstract
A detailed x-ray scattering study has been performed in the temperature range of the smectic- A phase for the liquid crystal compounds dodecylcyanobiphenyl (12CB) and octylcyanobiphenyl (8CB) confined in different controlled-pore glasses (CPGs) characterized by their average void radius R . On decreasing the temperature in bulk samples the layer thickness is increasing for 12CB and decreasing for 8CB, respectively. In nontreated CPG samples the layers dilate significantly with respect to the bulk liquid crystal. In order to explain the layer thickness behavior on varying temperature and R , one has to take into account molecular details of the liquid crystalline samples as well as memory effects.
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Affiliation(s)
- George Cordoyiannis
- National Centre for Scientific Research "Demokritos," 153 10 Aghia Paraskevi, Greece and Jozef Stefan Institute, 1001 Ljubljana, Slovenia.
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Brás AR, Dionísio M, Schönhals A. Confinement and Surface Effects on the Molecular Dynamics of a Nematic Mixture Investigated by Dielectric Relaxation Spectroscopy. J Phys Chem B 2008; 112:8227-35. [DOI: 10.1021/jp802133e] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- A. R. Brás
- REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Federal Institute of Materials Research and Testing (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
| | - M. Dionísio
- REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Federal Institute of Materials Research and Testing (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
| | - A. Schönhals
- REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Federal Institute of Materials Research and Testing (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
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Leys J, Glorieux C, Thoen J. Accelerated dielectric relaxation in the isotropic phase of associating liquid crystals dispersed with aerosils. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:061707. [PMID: 18643287 DOI: 10.1103/physreve.77.061707] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2008] [Indexed: 05/26/2023]
Abstract
The dielectric response of liquid crystals in their nematic phase shows an acceleration of the relaxation associated with the rotation around the short molecular axis when dispersed with aerosils. However, in the isotropic phase, this acceleration is only seen for certain liquid crystalline molecules. In this paper, an associating liquid crystal (5CB) and a shorter monotropic liquid crystalline member of the same homologous series (4CB), a liquid crystal that does not show association (5NCS) and a nonassociating liquid crystal (5O5) have been studied by dielectric spectroscopy in the isotropic phase. Both 4CB and 5CB show a constant acceleration in the isotropic phase, observed over a broad temperature range. 5NCS and 5O5 do not show an acceleration in their isotropic phase. It seems that the disturbance of the dipole-dipole association process for the associating molecules is an important factor in the explanation of the acceleration of the relaxation in the isotropic phase.
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Affiliation(s)
- Jan Leys
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D-bus 2416, Leuven, Belgium
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Pérez-Jubindo MA, de la Fuente MR, Diez-Berart S, López DO, Salud J. Influence of Cylindrical Submicrometer Confinement on the Static and Dynamic Properties in Nonyloxycyanobiphenyl (9OCB). J Phys Chem B 2008; 112:6567-77. [DOI: 10.1021/jp800119s] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. A. Pérez-Jubindo
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
| | - M. R. de la Fuente
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
| | - S. Diez-Berart
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
| | - D. O. López
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
| | - J. Salud
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
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Ramazanoglu M, Larochelle S, Garland CW, Birgeneau RJ. High-resolution x-ray scattering study of the effect of quenched random disorder on the nematic-smectic-A transition. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:061705. [PMID: 17677281 DOI: 10.1103/physreve.75.061705] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2006] [Revised: 03/28/2007] [Indexed: 05/16/2023]
Abstract
Using high-resolution x-ray scattering, the effect of quenched random disorder (QRD) on the second-order nematic-smectic-A (N-SmA) phase transition in butyloxybenzilidene-octylaniline (4O.8) has been studied. 4O.8 is a nonpolar liquid crystal (LC) with a monomeric smectic-A phase. The QRD is created by aerosil nanoparticles which gelate to form a three-dimensional network, confining the LC. The QRD caused by the aerosil gel generates quenched random fields acting on both the nematic and smectic-A order parameters. This results in the destruction of the quasi-long-range order of the smectic-A phase. The x-ray scattering data are modeled with a structure factor composed of two terms, one thermal and one static, corresponding to the connected and disconnected susceptibilities, respectively. Unlike previous studies, the two parts of the structure factor are decoupled by allowing different thermal and static correlation lengths. Our fitting procedure involves temperature-dependent and temperature-independent (global) variables. The amplitude and the parallel correlation length for the thermal part of the line-shape show critical-like behavior both above and below the transition temperature. Detailed analysis reveals that the thermal correlation length does not truly diverge at the phase transition. This effect is discussed on the basis of a cutoff for the divergence caused by the random fields generated by the aerosil network confining the liquid crystal. The intensity of the static term in the line-shape behaves like the order parameter squared at a conventional second-order phase transition. The effective order parameter critical exponent shows an evolution with increasing aerosil gel density ranging from the Gaussian tricritical value to the 3D- XY value. The results of a pseudocritical scaling analysis are compared to an analysis of 4O.8+aerosil heat capacity data and discussed using a phenomenological correlation between the nematic range of pure liquid crystals and the aerosil mass density, rho{s}.
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Affiliation(s)
- M Ramazanoglu
- Department of Physics, University of Toronto, Ontario M5S 1A7, Canada
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Liang D, Leheny RL. Smectic liquid crystals in an anisotropic random environment. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:031705. [PMID: 17500709 DOI: 10.1103/physreve.75.031705] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2006] [Indexed: 05/15/2023]
Abstract
We report a high-resolution x-ray scattering study of the smectic liquid crystal octylcyanobiphenyl (8CB) confined to aligned colloidal aerosil gels. The aligned gels introduce orientational fields that promote long-range nematic order while imposing positional random fields that couple to the smectic density wave and disrupt the formation of an ordered smectic phase. At low densities of aerosil, the low-temperature scattering intensity is consistent with the presence of a topologically ordered XY Bragg glass phase that is predicted to form in response to such anisotropic quenched disorder. The observed features of the phase include an algebraic decay of the smectic correlations, which is truncated at large length scales due to the imperfect nematic order, and a power-law exponent that agrees closely with the universal value predicted for the XY Bragg glass. At higher aerosil densities, deviations from the XY Bragg glass form are apparent. At high temperature, the scattering intensity displays pretransitional dynamic fluctuations associated with the destroyed nematic to smectic-A transition. The fluctuations obey quasicritical behavior over an extended range of reduced temperature. The effective critical exponents for the correlation lengths and smectic susceptibility differ systematically from those of pure 8CB, indicating that coupling of the nematic order to the gel suppresses its role in the smectic critical behavior.
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Affiliation(s)
- Dennis Liang
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
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22
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Cordoyiannis G, Kralj S, Nounesis G, Kutnjak Z, Zumer S. Pretransitional effects near the smectic-A -smectic-C* phase transition of hydrophilic and hydrophobic aerosil networks dispersed in ferroelectric liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:021702. [PMID: 17358355 DOI: 10.1103/physreve.75.021702] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Indexed: 05/14/2023]
Abstract
A detailed x-ray scattering and high-resolution ac calorimetric study has been carried out near the smectic-A to chiral smectic-C phase transition of liquid-crystal compounds 4-(2-methyl butyl) phenyl 4-n-octylbiphenyl-4-carboxylate (CE8) and p-( n-decyloxy) benzylidene-p-amino-(2-methylbutyl) cinnamate (DOBAMBC) confined in hydrophilic and hydrophobic aerosil nanoparticle networks. The character of the transition, which is mean field near a tricritical point in bulk, is changed dramatically with an increase of aerosil-induced disorder. X-ray measurements revealed pretransitional behavior and compression of the smectic layers, phenomena that are strongly pronounced in high aerosil concentrations. A theoretical model that takes into account the interplay of relevant mechanisms is proposed to explain the observed phenomena. The effect of chirality on the interaction of liquid crystals with aerosils is discussed.
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Affiliation(s)
- George Cordoyiannis
- National Centre for Scientific Research Demokritos, 153 10 Aghia Paraskevi, Greece
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Sharma D, MacDonald JC, Iannacchione GS. Role of Aerosil Dispersion on the Activated Kinetics of the LC1-xSilx System. J Phys Chem B 2006; 110:26160-9. [PMID: 17181271 DOI: 10.1021/jp065209z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This study explores the role of aerosil dispersion on activated phase transitions of bulk octylcyanobiphenyl (8CB) liquid crystals by performing heating rate-dependent experiments. Differential scanning calorimetry (DSC) was used at various heating ramp rates in order to probe the activated phase dynamics of the system. The system, LC1-xSilx, was prepared by mixing aerosil nanoparticles (7 nm in diameter) in the bulk 8CB by the solvent dispersion method (SDM). LC represents bulk 8CB, and Sil represents aerosil nanoparticles with concentration x in percent. The concentration of the aerosil nanoparticles (x) varied from 0 to 0.2 g/cm3 in the bulk 8CB. Well-defined, endothermic peaks were found on a heating scan at melting and at the smectic-A to nematic (SmA-N) and nematic to isotropic (N-I) transitions. These peaks show a temperature shift and a change in their shapes and sizes in the presence of aerosil nanoparticles. In addition, an exothermic peak also appeared before the melting peak during the heating scan in the presence of aerosil nanoparticles. All transitions shifted significantly with different heating ramp rates, following an Arrhenius behavior, showing activated kinetics. The presence of aerosil nanoparticles caused a significant increase in the enthalpy and a decrease in the activation energy compared to the results found in bulk 8CB. This behavior can be explained by aerosil dispersion in the LC1-xSilx, inducing a disorder in the bulk 8CB. Infrared (IR) spectroscopy shows a shift to higher frequency for the broad peak at 1082 cm-1, corresponding to an Si-O bond as the density of the aerosil increases, and can be explained in terms of surface and molecular interactions between aerosil nanoparticles and 8CB liquid crystal molecules.
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Affiliation(s)
- Dipti Sharma
- Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, USA
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On the influence of cylindrical sub-micrometer confinement on heptyloxycyanobiphenyl (7OCB). A dynamic dielectric study. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.03.072] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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25
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Sinha G, Leys J, Glorieux C, Thoen J. Dielectric spectroscopy of aerosil-dispersed liquid crystal embedded in Anopore membranes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 72:051710. [PMID: 16383623 DOI: 10.1103/physreve.72.051710] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2005] [Revised: 09/01/2005] [Indexed: 05/05/2023]
Abstract
The complex dielectric permittivity epsilon* values are presented for aerosil-dispersed 4-pentyl-4-cyanobiphenyl (5CB) confined in Anopore membranes. The dielectric permittivities are measured in the frequency range from 10(-2) Hz to 1 GHz at temperatures ranging from 50 degrees C down to -20 degrees C. In bulk 5CB, which has only a nematic phase, there exist two main relaxation processes: one due to the rotation of molecules around their short axes for parallel orientation of the director to the probing field and another fast relaxation process due to the librational motion of molecules for perpendicular orientation. Inside Anopore membranes both these main relaxation processes can be observed, but with subtle differences. The relaxation process due to the rotation of molecules around the short axis is faster in Anopores at all temperatures in comparison with the bulk process. Hydrophilic aerosil particles, when dispersed in the liquid-crystal (LC) phase, attach to each other via hydrogen bonds and form a three-dimensional interconnecting aerosil network, thus dividing the LC phase into small domains. Dispersing 5CB with different concentrations of hydrophilic aerosils leads to a decrease in relaxation time with aerosil concentration. In these dispersed systems a slow additional relaxation process emerges. This slow process becomes stronger with higher concentrations of aerosil. From our experiments we conclude that this process is the relaxation of 5CB molecules homeotropically aligned to the surface of the aerosil particles. In the case of 5CB-aerosil dispersions enclosed in Anopore membranes this slow process still exists and increases also with aerosil concentration. The relaxation time of the rotation of the 5CB molecules around their short axis systematically increases in these 5CB-aerosil samples in Anopore membranes with aerosil concentration from the 5CB-Anopore behavior towards the behavior observed for 5CB-aerosil dispersions. We explain the evolution as resulting from opposing tendencies from size effects (in the Anopore membranes) and disorder effects (in the aerosil dispersions).
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Affiliation(s)
- G Sinha
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
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Zakharov AV, Thoen J. Effect of aerosil dispersions on the nematic-to-isotropic interface. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2005; 17:447-53. [PMID: 16049623 DOI: 10.1140/epje/i2004-10150-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2004] [Accepted: 06/03/2005] [Indexed: 05/03/2023]
Abstract
The effect of silica aerosils on the kinetics of the first-order nematic-isotropic (NI) phase transition is phenomenologically described in the framework of the time-dependent Landau-Ginzburg equation. A steady-state solution to the equation is presented such that the NI interface may propagate with a solitary-like wave profile under constant quenching. The results provide a plausible basis for the interpretation of the dynamical effects of quenched disorder in the liquid-crystal systems, caused by randomly interconnected porous media, such as aerosils. In the low silica aerosil rho(s) ( < or =0.1 g/cm;3) regime, the calculated values of the interface velocity v(T,rho(s)), the interface thickness kappa(T,rho(s)), and the critical radius of a spherical nucleus of new nematic phase in a bulk isotropic environment, composed of polar molecules, such as 4-n-octyl- 4(')- cyanobiphenyl and 4-n-heptyl- 4(')- cyanobiphenyl shows that the effect of silica aerosils on the kinetics is reflected in a shifting of the set of temperature-dependent curves to lower temperature values.-1.
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Affiliation(s)
- A V Zakharov
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
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27
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Leys J, Sinha G, Glorieux C, Thoen J. Influence of nanosized confinements on 4-n-decyl-4'-cyanobiphenyl (10CB): a broadband dielectric study. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 71:051709. [PMID: 16089553 DOI: 10.1103/physreve.71.051709] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2004] [Indexed: 05/03/2023]
Abstract
Real (epsilon') and imaginary (epsilon") parts of the complex dielectric permittivity (epsilon*) of the liquid crystal (LC) 4-n-decyl-4'-cyanobiphenyl (10CB) embedded in Anopore membranes and Vycor porous glass, as well as dispersed with hydrophilic aerosils, have been studied by means of broadband dielectric spectroscopy in the frequency range from 10(-2) Hz to 1 GHz . In bulk 10CB, which has a direct transition from an isotropic to a smectic- A phase, there exists one main relaxation process for the parallel orientation of the director with respect to the probing field and a faster one for the perpendicular orientation. All molecular relaxation processes in 10CB are of Debye type and have Arrhenius like temperature dependence. For 10CB embedded in untreated and surface treated cylindrical pores of Anopore membranes the dielectric spectra are similar to the bulk with the exception that both the rotation around the short axis and the libration motion are faster in the pores. In the case of 10CB dispersed with two different concentrations of hydrophilic aerosils an emergence of a slow relaxation process, which is stronger for the higher concentration, is additionally observed along with the bulklike processes. The slow process in the LC-hydrophilic aerosil system is attributed to the relaxation of the molecules that are homeotropically aligned close to the surfaces of the aerosil particles. This process also has an Arrhenius type of temperature dependence. For 10CB embedded in narrow channels of Vycor porous glass three relaxation processes are observed. Two of these processes are bulklike and are due to the librational motion of molecules and the rotation of molecules around their short axes. The slowest process seems to be a surface process, similar in origin to that observed for 10CB dispersed with hydrophilic aerosils, and is prominent amongst all. The material in the Vycor porous glass could be supercooled by at least 185 degrees below bulk crystallization temperature. The slow process has a Vogel-Fulcher-Tamman (VFT) type of temperature dependence typical for glass formers in this wide temperature range. In addition, the bulklike processes are found to be strongly modified and also have a VFT like temperature dependence from measurements done in a wide temperature range. This behavior is in contrast to other reports of glassy behavior in confined LC, where the glassy behavior as concluded from a slow relaxation process observed in a narrow temperature range.
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Affiliation(s)
- J Leys
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
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28
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A comparison of the effects of dispersed hydrophobic or hydrophilic aerosil nanoparticles on the order and dynamics of the 5CB liquid crystal. Chem Phys Lett 2004. [DOI: 10.1016/j.cplett.2004.08.081] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Feldman DE, Pelcovits RA. Liquid crystals in random porous media: disorder is stronger in low-density aerosils. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 70:040702. [PMID: 15600389 DOI: 10.1103/physreve.70.040702] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2004] [Indexed: 05/24/2023]
Abstract
The nature of glass phases of liquid crystals in random porous media depends on the effective disorder strength. We study how the disorder strength depends on the density of the porous media and demonstrate that it can increase as the density decreases. We also show that the interaction of the liquid crystal with random porous media can destroy long-range order inside the pores.
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Affiliation(s)
- D E Feldman
- Department of Physics, Brown University, Providence, Rhode Island 02912, USA
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30
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Kralj S, Popa-Nita V. Random anisotropy nematic model: connection with experimental systems. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2004; 14:115-125. [PMID: 15254831 DOI: 10.1140/epje/i2003-10144-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We study theoretically the phase behavior of the continuum Random Anisotropy Nematic model. A domain-type pattern is assumed to appear in a distorted nematic liquid crystal (LC) phase. We map the model parameters to physical quantities characterizing LCs confined to Controlled-Pore Glasses and LC-aerosil dispersions. The domain size dependence on the disorder strength is obtained in accordance with the Imry-Ma prediction. The model estimates for temperature shifts of the paranematic-nematic phase transition and for the critical point, where this transition ceases to exist, are compared to the available experimental results.
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Affiliation(s)
- S Kralj
- Laboratory of Physics of Complex Systems, Faculty of Education, University of Maribor, Koroska 160, 2000, Maribor, Slovenia.
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31
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Sinha G, Glorieux C, Thoen J. Broadband dielectric spectroscopy study of molecular dynamics in the glass-forming liquid crystal isopentylcyanobiphenyl dispersed with aerosils. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 69:031707. [PMID: 15089310 DOI: 10.1103/physreve.69.031707] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2003] [Indexed: 05/24/2023]
Abstract
The glass-forming liquid crystal isopentylcyanobiphenyl (CB15) filled with different concentrations of hydrophilic and hydrophobic aerosils has been investigated by broadband dielectric spectroscopy in the frequency range from 10(-2) Hz to 10(7) Hz over a temperature range of 173 K-300 K. CB15 that consists of chiral molecules has a monotropic system of phases nematic (N*) and smectic-A upon supercooling and forms a glass further on. In the isotropic phase a single Davidson-Cole process exists in the substance, which is due to the rotation of the molecules around their short axes. In the supercooled N* phase a Cole-Cole process that is an order of magnitude faster is additionally present and is due to the rotation in a cone around the local director. The relaxation times of the process due to rotation around short axes obey the empirical Vogel-Fulcher-Tamman behavior typical for glass-forming systems. Filling of the liquid crystal (LC) with different concentrations of hydrophilic aerosils leads to the emergence of a slow relaxation process that grows with the increasing concentration of the aerosils. The aerosil particles, which form a three-dimensional network dividing the LC phase into domains, have little effect on the relaxation times of the bulk processes. As a consequence the glass transition temperature is merely affected. On the other hand, in LCs dispersed with hydrophobic aerosils the slow process is quite weak. The slow process is attributed to the relaxation of the molecules that are homeotropically attached at the surfaces of the aerosil particles. The LC-aerosil surface interaction leads to a considerable slowing down of the molecular rotation around their short axis. The process has an Arrhenius-like temperature dependence of the relaxation times with an activated type of dynamics, which can be explained by considering a nonincreasing rearranging region of cooperativity in surface layers.
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Affiliation(s)
- G Sinha
- Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
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32
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Boussoualem M, Roussel F, Ismaili M. Thermophysical, dielectric, and electro-optic properties of nematic liquid crystal droplets confined to a thermoplastic polymer matrix. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 69:031702. [PMID: 15089305 DOI: 10.1103/physreve.69.031702] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2003] [Indexed: 05/24/2023]
Abstract
The thermophysical, dielectric and electro-optic properties of polymer-dispersed liquid crystal (PDLC) films made of monodisperse polystyrene (PS) and 4-n-pentyl-4(')-cyanobiphenyl (5CB) are investigated by polarized optical microscopy, differential scanning calorimetry, ac impedance analysis, and forward transmittance measurement technique. The PS-5CB system exhibits an upper critical solution temperature (UCST) shape phase diagram with a wide isotropic+isotropic (I+I) miscibility gap between the isotropic and nematic+isotropic (N+I) regions. An absorption domain in the dielectric spectrum of PDLC films was clearly observed at low frequency, and unambiguously assigned to the confined liquid crystalline phase in both nematic and isotropic states. The correlation between the dielectric and electro-optical results for PS-5CB (30:70) samples has shown that in the vicinity of the low frequency absorption domain ( approximately 200 Hz at T=25 degrees C), a drastic decrease in the optical transmittance of the film occurs. This phenomenon can be related to an interfacial polarization process resulting from a charge accumulation at the droplet-polymer interface (Maxwell-Wagner-Sillars effect).
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Affiliation(s)
- Mourad Boussoualem
- Laboratoire de Thermophysique de la Matière Condensée, Equipe de l'UMR CNRS 8024, Université du Littoral-Côte d'Opale, MREI, 59140 Dunkerque, France
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33
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Zakharov AV, Thoen J. Effect of silica aerosils on the nematic to isotropic transition: A theoretical treatment. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 69:011704. [PMID: 14995637 DOI: 10.1103/physreve.69.011704] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2003] [Revised: 09/04/2003] [Indexed: 05/24/2023]
Abstract
The effect of silica aerosils on a first-order nematic-isotropic (NI) transition temperature shift DeltaT(NI)(rho(s)) and on the enthalpy jump DeltaH(rho(s)) is phenomenologically described in the framework of the Landau-de Gennes theory. It is shown that the aerosil network dispersed in the liquid crystal phase creates an additional curvature perturbation, resulting in linear and nonlinear slopes both in the transition temperature shift DeltaT(NI)(rho(s))=-T(NI)(0)alpharho(s) and in the enthalpy jump DeltaH(rho(s))=1 / 4DeltaH(0)(1+sqrt[1-kapparho(s)])(2)(1-alpharho(s)), where rho(s) is the aerosil density, and both alpha and kappa are constants of the theory. In the low rho(s)(</=0.2 g/cm(3)) regime, both the calculated and the measured values of DeltaH(rho(s)) for polar liquid crystals, such as 4-n-octyl-4(')-cyanobiphenyl (8CB) and 4-n-heptyl-4(')-cyanobiphenyl (7CB) show a good agreement between theory and experiment. The comparisons between the calculated and measured values of DeltaT(NI)(rho(s)), in the low-rho(s) regime, show a better agreement in the 7CB+aerosil than in the 8CB+aerosil systems.
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Affiliation(s)
- A V Zakharov
- Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan, Leuven, Belgium.
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34
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Leheny RL, Park S, Birgeneau RJ, Gallani JL, Garland CW, Iannacchione GS. Smectic ordering in liquid-crystal-aerosil dispersions. I. X-ray scattering. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 67:011708. [PMID: 12636518 DOI: 10.1103/physreve.67.011708] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2002] [Indexed: 05/24/2023]
Abstract
Comprehensive x-ray scattering studies have characterized the smectic ordering of octylcyanobiphenyl (8CB) confined in the hydrogen-bonded silica gels formed by aerosil dispersions. For all densities of aerosil and all measurement temperatures, the correlations remain short range, demonstrating that the disorder imposed by the gels destroys the nematic (N) to smectic-A (SmA) transition. The smectic correlation function contains two distinct contributions. The first has a form identical to that describing the critical thermal fluctuations in pure 8CB near the N-SmA transition, and this term displays a temperature dependence at high temperatures similar to that of the pure liquid crystal. The second term, which is negligible at high temperatures but dominates at low temperatures, has a shape given by the thermal term squared and describes the static fluctuations due to random fields induced by confinement in the gel. The correlation lengths appearing in the thermal and disorder terms are the same and show a strong variation with gel density at low temperatures. The temperature dependence of the amplitude of the static fluctuations further suggests that nematic susceptibility becomes suppressed with increasing quenched disorder. The results overall are well described by a mapping of the liquid-crystal-aerosil system onto a three-dimensional XY model in a random field with disorder strength varying linearly with the aerosil density.
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Affiliation(s)
- R L Leheny
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
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35
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Kutnjak Z, Kralj S, Zumer S. Effect of dispersed silica particles on the smectic-A-smectic-C* phase transition. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 66:041702. [PMID: 12443218 DOI: 10.1103/physreve.66.041702] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2002] [Indexed: 05/24/2023]
Abstract
We study the influence of the dispersed aerosil particle concentration on the soft and Goldstone mode dynamics across the smectic-A-smectic-C* phase transition using dielectric spectroscopy. We use CE8 liquid crystal filled with aerosils of concentrations x=m(s)/(m(s)+m(LC))=0.025, 0.05, 0.1, and 0.15, where m(s) and m(LC) stand for masses of aerosil and liquid crystal, respectively. In dispersions with x<0.15 the characteristic Goldstone frequency temperature dependence f(G)(T) is almost bulklike in contrast to the corresponding soft mode dependence f(s)(T). For x>0 the degeneracy of the modes at the SmA-SmC* transition temperature is lifted. With increasing x the modes' intensities gradually decrease and the critical effective coefficient gamma tentatively approaches the value characterizing the three-dimensional XY universality class. For x=0.15, a drastic change in behavior is observed. The Goldstone mode is completely suppressed and the f(s)(T) dependence begins to deviate from the Arrhenius behavior. A simple phenomenological approach is used in the explanation of results.
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Affiliation(s)
- Z Kutnjak
- Condensed Matter Physics Department, Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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36
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Arcioni A, Bacchiocchi C, Grossi L, Nicolini A, Zannoni C. Electron Spin Resonance Studies of Order and Dynamics in a Nematic Liquid Crystal Containing a Dispersed Hydrophobic Aerosil. J Phys Chem B 2002. [DOI: 10.1021/jp020554j] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Alberto Arcioni
- Dipartimento di Chimica Fisica e Inorganica, Università, Viale Risorgimento 4, I-40136 Bologna, Italy, and Dipartimento di Chimica Organica “A. Mangini”, Università, Viale Risorgimento 4, I-40136 Bologna, Italy
| | - Corrado Bacchiocchi
- Dipartimento di Chimica Fisica e Inorganica, Università, Viale Risorgimento 4, I-40136 Bologna, Italy, and Dipartimento di Chimica Organica “A. Mangini”, Università, Viale Risorgimento 4, I-40136 Bologna, Italy
| | - Loris Grossi
- Dipartimento di Chimica Fisica e Inorganica, Università, Viale Risorgimento 4, I-40136 Bologna, Italy, and Dipartimento di Chimica Organica “A. Mangini”, Università, Viale Risorgimento 4, I-40136 Bologna, Italy
| | - Alessandro Nicolini
- Dipartimento di Chimica Fisica e Inorganica, Università, Viale Risorgimento 4, I-40136 Bologna, Italy, and Dipartimento di Chimica Organica “A. Mangini”, Università, Viale Risorgimento 4, I-40136 Bologna, Italy
| | - Claudio Zannoni
- Dipartimento di Chimica Fisica e Inorganica, Università, Viale Risorgimento 4, I-40136 Bologna, Italy, and Dipartimento di Chimica Organica “A. Mangini”, Università, Viale Risorgimento 4, I-40136 Bologna, Italy
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37
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Jamée P, Pitsi G, Thoen J. Systematic calorimetric investigation of the effect of silica aerosils on the nematic to isotropic transition in heptylcyanobiphenyl. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 66:021707. [PMID: 12241196 DOI: 10.1103/physreve.66.021707] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2002] [Indexed: 05/23/2023]
Abstract
The effect of confinement on liquid crystal phase transitions was investigated in mixtures of the liquid crystal heptylcyanobiphenyl with hydrophilic aerosils. The influence of the aerosil density on the nematic to isotropic transition was studied by adiabatic scanning calorimetry. Mixtures have been investigated with an aerosil content between rho(S)=0.1 and rho(S)=0.7, the latter being substantially higher than that investigated in previous studies with other liquid crystal-aerosil mixtures. The transitions in the examined mixtures exhibited an unusually large broadening, while the transition temperatures showed peculiar behavior. Notwithstanding, the transition (latent) heat behaved as could be expected on the basis of previous studies. The observed behavior can be explained, in the context of the elastic-strain approach usually employed to describe transition temperature shifts, by variations in the distribution of the radius of curvature R of the aerosil voids originating from sample preparation. It is important in this regard to separate the behavior of the transition temperatures and the transition (latent) heats, the former being influenced by the radius of curvature of the voids and the latter by the total void surface per unit volume. Three quantitative models were compared with experimental results. Both the pinned boundary layer and the random field model yield an evolution of transition temperatures not in agreement with experimental observations. More importantly, they predict a decrease of the pretransitional specific heat capacity, not supported by experiment. The difficulties with these models are avoided in a third, mean-field surface-induced order model.
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Affiliation(s)
- P Jamée
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
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Retsch CC, McNulty I, Iannacchione GS. Elastic coupling of silica gel dynamics in a liquid-crystal-aerosil dispersion. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:032701. [PMID: 11909129 DOI: 10.1103/physreve.65.032701] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2001] [Indexed: 05/23/2023]
Abstract
The dynamics of a thixotropic silica aerosil gel dispersed in an octylcyanobiphenyl liquid crystal were directly probed by x-ray intensity fluctuation spectroscopy. For all samples, the time-autocorrelation function of the gel was well described by a modified-exponential function over the q range studied. Compared to a pure gel sample, a dilute (0.06 g cm(-3)) gel embedded within the liquid crystal displayed more complex and temperature dependent dynamics. Near the second-order smectic-A-to-nematic phase transition of the liquid crystal the gel relaxation became significantly more complex and slower (tau approximately 2150 s) compared to relaxations observed well within either phase. This clearly demonstrates coupling between the dynamics of the gel and the host liquid crystal, consistent with critical slowing down of smectic and director fluctuations. A random dampening field, elastically coupled to the liquid crystal, would explain the earlier observed crossover of this transition towards 3d-XY behavior.
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Affiliation(s)
- Cornelia C Retsch
- Experimental Facilities Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
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