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Thapa K, Iadlovska OS, Bisoyi HK, Paterson DA, Storey JMD, Imrie CT, Li Q, Shiyanovskii SV, Lavrentovich OD. Combined electric and photocontrol of selective light reflection at an oblique helicoidal cholesteric liquid crystal doped with azoxybenzene derivative. Phys Rev E 2021; 104:044702. [PMID: 34781517 DOI: 10.1103/physreve.104.044702] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2021] [Accepted: 09/16/2021] [Indexed: 11/07/2022]
Abstract
An oblique helicoidal cholesteric liquid crystal Ch_{OH} represents a unique optical material with a single-harmonic periodic modulation of the refractive index and a pitch that can be tuned by an electric or magnetic field in a broad range from submicrometers to micrometers. In this work, we demonstrate that the oblique helicoidal cholesteric doped with azoxybenzene molecules can be tuned by both the electric field and light irradiation. The tuning mechanism is explained by the kinetics of trans-cis photoisomerization of the azoxybenzene molecules. At a fixed voltage, UV irradiation causes a redshift of the reflection peak by more than 200 nm. The effect is caused by an increase of the bend elastic constant of Ch_{OH} under irradiation. The demonstrated principle has the potential for applications such as smart windows, sensors, tunable lasers, and filters.
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Affiliation(s)
- Kamal Thapa
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA.,Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - Olena S Iadlovska
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA.,Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - Hari Krishna Bisoyi
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - Daniel A Paterson
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, AB24 3UE Scotland, United Kingdom
| | - John M D Storey
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, AB24 3UE Scotland, United Kingdom
| | - Corrie T Imrie
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, AB24 3UE Scotland, United Kingdom
| | - Quan Li
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA.,Materials Science Graduate Program, Kent State University, Kent, Ohio 44242, USA
| | - Sergij V Shiyanovskii
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA.,Materials Science Graduate Program, Kent State University, Kent, Ohio 44242, USA
| | - Oleg D Lavrentovich
- Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA.,Department of Physics, Kent State University, Kent, Ohio 44242, USA.,Materials Science Graduate Program, Kent State University, Kent, Ohio 44242, USA
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Paoloni S, Mercuri F, Marinelli M, Pizzoferrato R, Zammit U, Kosa T, Sukhomlinova L, Taheri B. Simultaneous calorimetric and polarization microscopy investigations of light induced changes over phase transitions in a liquid crystal-napthopyran mixture. J Chem Phys 2015; 143:134901. [PMID: 26450328 DOI: 10.1063/1.4931822] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have studied the specific heat and the thermal conductivity in a 4-(n-octyl)-4'-cyanobiphenyl liquid crystal (LC)-photochromic molecules mixture, before, during, and after the photo-activation of the dispersed photochromic molecules, over both the smectic A-nematic and the nematic-isotropic phase transitions. The evaluation of the specific heat has enabled the determination of the changes of the phase transition characteristics induced by the photochromic molecules photoisomerization, while that of the thermal conductivity could be used to monitor the modifications induced in the average LC molecular orientation. The polarization microscopy imaging of the sample texture constituted a valuable support for the interpretation of the obtained thermal conductivity results.
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Affiliation(s)
- S Paoloni
- Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, 00133 Rome, Italy
| | - F Mercuri
- Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, 00133 Rome, Italy
| | - M Marinelli
- Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, 00133 Rome, Italy
| | - R Pizzoferrato
- Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, 00133 Rome, Italy
| | - U Zammit
- Dipartimento di Ingegneria Industriale, Università di Roma "Tor Vergata," Via del Politecnico 1, 00133 Rome, Italy
| | - T Kosa
- Alpha Micron, Inc., Kent, Ohio 44240, USA
| | | | - B Taheri
- Alpha Micron, Inc., Kent, Ohio 44240, USA
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Kumar MV, Prasad SK, Rao DSS, Mukherjee PK. Competition between anisometric and aliphatic entities: an unusual phase sequence with the induction of a phase in an n-alkane-liquid crystal binary system. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:4465-4473. [PMID: 24678973 DOI: 10.1021/la500367y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this work, we demonstrate two important features that arise out of introducing a liquid-crystalline (LC) compound into the rotator phase matrix and the consequent competition between the anisometric segments of the LC moieties and the aliphatic units. First, we show that the change in the structural character of the mixed medium depends on which of the entities forms the minority concentration: in the case of this being the alkane, the two components of the binary system are nanophase segregated, whereas if the LC molecules are present in a small concentration, then the layered structure merely gets roughened without any segregation. The second and more significant result of the calorimetric and X-ray experiments, at low LC concentrations, is the induction of a rotator phase that leads to unusual phase sequence not reported hitherto. Possible scenarios for the molecular arrangement are discussed. A Landau model is also presented that explains some of the observed features.
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Affiliation(s)
- M Vijay Kumar
- Centre for Soft Matter Research, Jalahalli, Bangalore 560 013, India
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Abstract
Colloidal particles in a liquid crystal (LC) behave very differently from their counterparts in isotropic fluids. Elastic nature of the orientational order and surface anchoring of the director cause long-range anisotropic interactions and lead to the phenomenon of levitation. The LC environment enables new mechanisms of particle transport that are reviewed in this work. Among them the motion of particles caused by gradients of the director, and effects in the electric field: backflow powered by director reorientations, dielectrophoresis in LC with varying dielectric permittivity and LC-enabled nonlinear electrophoresis with velocity that depends on the square of the applied electric field and can be directed differently from the field direction.
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Nicoletta FP, Cupelli D, Formoso P, De Filpo G, Colella V, Gugliuzza A. Light responsive polymer membranes: a review. MEMBRANES 2012; 2:134-97. [PMID: 24957966 PMCID: PMC4021883 DOI: 10.3390/membranes2010134] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 02/04/2012] [Accepted: 02/16/2012] [Indexed: 12/04/2022]
Abstract
In recent years, stimuli responsive materials have gained significant attention in membrane separation processes due to their ability to change specific properties in response to small external stimuli, such as light, pH, temperature, ionic strength, pressure, magnetic field, antigen, chemical composition, and so on. In this review, we briefly report recent progresses in light-driven materials and membranes. Photo-switching mechanisms, valved-membrane fabrication and light-driven properties are examined. Advances and perspectives of light responsive polymer membranes in biotechnology, chemistry and biology areas are discussed.
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Affiliation(s)
| | - Daniela Cupelli
- Department of Pharmaceutical Sciences, Università della Calabria, I-87036 Rende (CS), Italy.
| | - Patrizia Formoso
- Department of Pharmaceutical Sciences, Università della Calabria, I-87036 Rende (CS), Italy.
| | - Giovanni De Filpo
- Department of Chemistry, Università della Calabria, I-87036 Rende (CS), Italy.
| | - Valentina Colella
- Department of Pharmaceutical Sciences, Università della Calabria, I-87036 Rende (CS), Italy.
| | - Annarosa Gugliuzza
- Institute on Membrane Technology-National Council Research, ITM-CNR, I-87030 Rende (CS), Italy.
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Prasad SK, Nair GG, Hegde G. Nonequilibrium Liquid Crystalline Layered Phase Stabilized by Light. J Phys Chem B 2006; 111:345-50. [PMID: 17214484 DOI: 10.1021/jp066404g] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The ability of light to alter/stabilize a particular thermodynamic phase is a power tool to investigate condensed matter from a new dimension. This field of photoinduced phase transitions is currently an important area of research. Being elastically soft and having subtle changes between its many phases a liquid crystal material is an attractive medium to investigate such light-driven phase transitions. The attraction is partly due to the large birefringence changes accompanying these transitions that are useful in developing photonic devices. In all of the cases reported to date, the photoinduced transition always leads to a phase that in any case exists in the thermal cycle. Recently we reported the first exception to such an established phenomenon (Adv. Mater. 2005, 17, 2086). The guest-host ternary mixture consisting of the photoactive azobenzene guest molecules does not exhibit smectic A phase in the absence of UV radiation. However, the smectic A phase is induced and stabilized only in the presence of UV light. In this paper, we map out hitherto unexplored temperature versus UV intensity phase diagrams for various mixtures, which illustrate that light mimics, in a limited sense, the role of a thermodynamic parameter such as, for example, pressure. The threshold UV intensity required to photodrive the appearance of the smectic A phase is seen to have a strong concentration dependence. Our studies also suggest the possibility of observing a double critical point by employing the UV intensity as a fine-tuning parameter.
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Affiliation(s)
- S Krishna Prasad
- Centre for Liquid Crystal Research, Jalahalli, Bangalore 560013, India.
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Zalar B, Lavrentovich OD, Zeng H, Finotello D. Deuteron NMR investigation of a photomechanical effect in a smectic-A liquid crystal. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:2252-2262. [PMID: 11088692 DOI: 10.1103/physreve.62.2252] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2000] [Indexed: 05/23/2023]
Abstract
Deuteron quadrupole-perturbed NMR is used to study the perturbation of orientational order in a smectic-A liquid crystal (octylcyanobiphenyl or 8CB) caused by photoinduced trans-to-cis isomerization of a photosensitive dopant (diheptylazobenzene or 7AB). The time and temperature dependences of the orientational order were independently studied for 8CB, 7AB, and their mixtures. Upon UV irradiation that causes trans-to-cis isomerization of 7AB, the orientational order parameter of the smectic-A phase is reduced. Relaxation in the dark exponentially restores the equilibrium value of the order parameter. The characteristic time for this process closely matches the lifetimes of the 7AB excited state. While in the 8CB smectic-A matrix, the cis-isomerized 7AB molecules retain a uniaxial orientational order with the director oriented along the normal to the smectic layers. The highly bent 7AB cis molecules act as a disorienting factor, decreasing the orientational order in the layers and causing a small increase in layer spacing. This disorder-induced increase in layer spacing is much smaller than the actual increase as observed by in situ x-ray experiments on UV-irradiated mixtures of 8CB:7AB. Concomitant with the experimental observation that only a fraction of 7AB molecules are converted to the cis state, this work provides indirect evidence for a nanophase segregation with the 7AB cis-isomers arranged within the interlayer space, thus significantly increasing the smectic layer spacing.
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Affiliation(s)
- B Zalar
- Jozef Stefan Institute, University of Ljubljana, Jamova 39, 1000 Ljubljana, Slovenia
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Lansac Y, Glaser MA, Clark NA, Lavrentovich OD. Photocontrolled nanophase segregation in a liquid-crystal solvent. Nature 1999. [DOI: 10.1038/17995] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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