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Full-Text Articles in Physics
Microcalorimetric Study Of Nematic-To-Neat-Soap And Nematic-To-Isotropic Phase Transitions In A Lyotropic Liquid Crystal, T. S. Shin, Satyendra Kumar
Microcalorimetric Study Of Nematic-To-Neat-Soap And Nematic-To-Isotropic Phase Transitions In A Lyotropic Liquid Crystal, T. S. Shin, Satyendra Kumar
Satyendra Kumar
The results of specific-heat measurements at the nematic- (N) to-neat-soap (NS) and nematic-to-isotropic (I) phase transitions in binary mixtures of cesium-perfluoro-octanoate and water are reported. The ratio of specific-heat amplitudes above and below the N-NS transition, A+/A-, and the specific-heat exponent α remain ∼1.0 and ≤0.02, respectively, suggesting 3D XY-type behavior. At the first-order N-I transition, vanishing latent heat and coexistence range at low concentration indicate the existence of a Landau point.
A Cellulose Liquid Crystal Motor: A Steam Engine Of The Second Kind, Yong Geng, Pedro Lucio Almeida, Cheng Cheng, Peter Palffy-Muhoray, Maria Helena Godinho, Susete Nogueira Fernandes
A Cellulose Liquid Crystal Motor: A Steam Engine Of The Second Kind, Yong Geng, Pedro Lucio Almeida, Cheng Cheng, Peter Palffy-Muhoray, Maria Helena Godinho, Susete Nogueira Fernandes
Peter Palffy-Muhoray
The salient feature of liquid crystal elastomers and networks is strong coupling between orientational order and mechanical strain. Orientational order can be changed by a wide variety of stimuli, including the presence of moisture. Changes in the orientation of constituents give rise to stresses and strains, which result in changes in sample shape. We have utilized this effect to build soft cellulose-based motor driven by humidity. The motor consists of a circular loop of cellulose film, which passes over two wheels. When humid air is present near one of the wheels on one side of the film, with drier air …
Pattern Formation In Non-Newtonian Hele-Shaw Flow, P. Fast, L. Kondic, M. J. Shelley, Peter Palffy-Muhoray
Pattern Formation In Non-Newtonian Hele-Shaw Flow, P. Fast, L. Kondic, M. J. Shelley, Peter Palffy-Muhoray
Peter Palffy-Muhoray
We study theoretically the Saffman-Taylor instability of an air bubble expanding into a non-Newtonian fluid in a Hele-Shaw cell, with the motivation of understanding suppression of tip-splitting and the formation of dendritic structures observed in the flow of complex fluids, such as polymeric liquids or liquid crystals. A standard visco-elastic flow model is simplified in the case of flow in a thin gap, and it is found that there is a distinguished limit where shear thinning and normal stress differences are apparent, but elastic response is negligible. This observation allows formulation of a generalized Darcy's law, where the pressure satisfies …
Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray
Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray
Peter Palffy-Muhoray
The distance of closest approach of hard particles is a key parameter of their interaction and plays an important role in the resulting phase behavior. For nonspherical particles, the distance of closest approach depends on orientation, and its calculation is surprisingly difficult. Although overlap criteria have been developed for use in computer simulations [ Vieillard-Baron J. Chem. Phys. 56 4729 (1972); Perram and Wertheim J. Comput. Phys. 58 409 (1985)], no analytic solutions have been obtained for the distance of closest approach of ellipsoids in three dimensions, or, until now, for ellipses in two dimensions. We have derived an analytic …
Effect Of Director Distortions On Morphologies Of Phase Separation In Liquid Crystals, D. Voloschenko, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich
Effect Of Director Distortions On Morphologies Of Phase Separation In Liquid Crystals, D. Voloschenko, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich
Oleg Lavrentovich
We study phase separation from a nematic liquid crystal with spatially nonuniform director gradients. Particles of a phase-separated component, which is either an isotropic fluid (silicone oil) or a nonmesogenic photopolymer, accumulate in the regions with the strongest director distortions, thus reducing the overall energy of the system.
Nanophase Segregation Of Nonpolar Solvents In Smectic Liquid Crystals Of Bent-Shape Molecules, M.Y.M. Huang, A.M. Pedreira, O.G. Martins, A.M.F. Neto, Antal Jakli
Nanophase Segregation Of Nonpolar Solvents In Smectic Liquid Crystals Of Bent-Shape Molecules, M.Y.M. Huang, A.M. Pedreira, O.G. Martins, A.M.F. Neto, Antal Jakli
Antal Jakli
Electro-optical, calorimetric, x-ray, and dielectric measurements are reported on a mixture containing a bent-core liquid crystal 4-chloro-1,3-phenylinebis [4-(4-n-tetradecyloxyphenyliminomethyl) benzoate] mixed with the nonpolar solvent n-hexadecane (HEX). It is observed that the addition of HEX depresses the isotropic-to-smectic phase transition temperature, but the crystallization temperature does not change considerably. Instead, the texture of the crystalline phase changes and, at sufficiently high concentrations of HEX (>20 wt %), an optically isotropic phase appears. Above 40 wt % HEX concentrations, the mesophase completely disappears and a direct isotropic solid-to-isotropic liquid transition takes place. At increasing HEX concentration, the transition enthalpies, the layer …
Light-Induced Changes Of Optical And Electrical Properties In Bent-Core Azo Compounds, Antal Jakli, V. Prasad, D.S.S. Rao, Guangxun Liao, I. Janossy
Light-Induced Changes Of Optical And Electrical Properties In Bent-Core Azo Compounds, Antal Jakli, V. Prasad, D.S.S. Rao, Guangxun Liao, I. Janossy
Antal Jakli
We have studied the optical and electrical properties of two bent-core substances with an azo linkage in their cores. Pump-probe laser studies, direct textural observations, and spectrophotometric recordings show an initial decrease of light transmission, which at larger light intensities (similar to 1 mW/mm(2)) is followed by a bleaching. Simultaneously the electrical properties (electric conductivity, antiferroelectric polarization, switching threshold, and switching time) decreased monotonically with increasing light intensities. The monotonic decrease of electrical properties indicates that the darkening and bleaching have the same origin, namely, the photochemical isomerization of the azo linkage from the trans to the cis isomer. The …
Synthesis Of Al2tio5 And Its Effect On The Properties Of Chitosan-Nh4scn Polymer Electrolytes, Siti Rohana Majid, Hassan F., Woo H. J., Aziz N. A., Kufian M. Z.
Synthesis Of Al2tio5 And Its Effect On The Properties Of Chitosan-Nh4scn Polymer Electrolytes, Siti Rohana Majid, Hassan F., Woo H. J., Aziz N. A., Kufian M. Z.
Siti Rohana Majid
In this paper, Al2TiO5 ceramic material has been synthesised and used as filler in polymer electrolyte system to enhance the conductivity. The precursor sintered at 1,050 A degrees C and contained 0.08 mole of aluminium nitrate gives the best and complete formation of Al2TiO5. Composite polymer electrolytes of chitosan-NH4SCN containing different amount of home-made Al2TiO5 were prepared by solution casting. The addition of filler has enhanced the conductivity of polymer electrolyte. The sample 57 wt% chitosan-38 wt% NH4SCN-5 wt% Al2TiO5 exhibited the highest electrical conductivity of 2.10 x 10(-4) S cm(-1) at room temperature. The presence of the Al2TiO5 creates …
Scaling Behavior Of The Exchange-Bias Training Effect, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo
Scaling Behavior Of The Exchange-Bias Training Effect, Christian Binek, Srinivas Polisetty, Sarbeswar Sahoo
Christian Binek
The dependence of the exchange-bias training effect on temperature and ferromagnetic film thickness is studied in detail and scaling behavior of the data is presented. Thickness-dependent exchange bias and its training are measured using the magneto-optical Kerr effect. A focused laser beam is scanned across a Co wedge probing local hysteresis loops of the Co film which is pinned by an antiferromagnetic CoO layer of uniform thickness. A phenomenological theory is best fitted to the exchange-bias training data resembling the evolution of the exchange-bias field on subsequently cycled hysteresis loops. Best fits are done for various temperatures and Co thicknesses. …
Random-Field Critical And Spin-Flop Behavior Of The Anisotropic Heisenberg Antiferromagnet Fe0.9mg0.1br2 In Axial Magnetic Fields, Christian Binek
Random-Field Critical And Spin-Flop Behavior Of The Anisotropic Heisenberg Antiferromagnet Fe0.9mg0.1br2 In Axial Magnetic Fields, Christian Binek
Christian Binek
Faraday optical measurements on the dilute hexagonal antiferromagnet Fe0.85Mg0.15Br2 in an external axial field reveal a spin-flop phase line ending at a multicritical point (Tm=8.1 K, Hm=1050 kA m-1) and crossover from random-exchange to random-field Ising criticality with an exponent Phi =1.40+or-0.04 in the vicinity of TN=11.1 K. Cusp-like behaviour of the specific heat at TN is discussed in view of recent Monte Carlo results.
Preparation And Characterization Of Magnesium Ion Gel Polymer Electrolytes For Application In Electrical Double Layer Capacitors, Siti Rohana Majid, Asmara S. N., Kufian M. Z., Arof A. K.
Preparation And Characterization Of Magnesium Ion Gel Polymer Electrolytes For Application In Electrical Double Layer Capacitors, Siti Rohana Majid, Asmara S. N., Kufian M. Z., Arof A. K.
Siti Rohana Majid
This work describes the preparation and characterization of poly (methyl methacrylate) (PMMA) based gel polymer electrolytes with magnesium triflate (Mg(CF(3)SO(3))(2)) as the ion providing salt. Liquid electrolytes containing 0.4 M Mg(CF(3)SO(3))(2) in solvents comprising different ratios of ethylene carbonate (EC) and diethyl carbonate (DEC) have been prepared at room temperature. The highest conducting electrolyte contains EC and DEC in the weight ratio of 2:1. To the highest conducting liquid electrolyte, 25-50 wt.% PMMA has been added and the mixtures were heated at 80 degrees C for 2 min to form gel polymer electrolytes. The gel electrolyte with composition 40 wt.% …
Self-Assembly, Condensation, And Order In Aqueous Lyotropic Chromonic Liquid Crystals Crowded With Additives, Luana Tortora, Heung-Shik Park, Shin-Woong Kang, Victoria Savaryn, Seung-Ho Hong, Konstantine Kaznatcheev, Daniele Finotello, Samuel Sprunt, Satyendra Kumar, Oleg Lavrentovich
Self-Assembly, Condensation, And Order In Aqueous Lyotropic Chromonic Liquid Crystals Crowded With Additives, Luana Tortora, Heung-Shik Park, Shin-Woong Kang, Victoria Savaryn, Seung-Ho Hong, Konstantine Kaznatcheev, Daniele Finotello, Samuel Sprunt, Satyendra Kumar, Oleg Lavrentovich
Oleg Lavrentovich
Dense multicomponent systems with macromolecules and small solutes attract a broad research interest as they mimic the molecularly crowded cellular interiors. The additives can condense and align the macromolecules, but they do not change the degree of covalentpolymerization. We chose a lyotropic chromonic liquid crystal with reversibly and non-covalently assembled aggregates as a much softer system, reminiscent of “living polymers”, to demonstrate that small neutral and charged additives cause condensation of aggregates with ensuing orientational and positional ordering and nontrivial morphologies of phase separation, such as tactoids and toroids of the nematic and hexagonal columnar phase coexisting with the isotropic …
Bent-Core Liquid Crystal Elastomers, Rafael Verduzco, Paul Luchette, Seung Ho Hong, John Harden, Elaine Dimasi, Peter Palffy-Muhoray, S. Michael Kilbey Ii, Jim T. Gleeson, Antal Jákli
Bent-Core Liquid Crystal Elastomers, Rafael Verduzco, Paul Luchette, Seung Ho Hong, John Harden, Elaine Dimasi, Peter Palffy-Muhoray, S. Michael Kilbey Ii, Jim T. Gleeson, Antal Jákli
Peter Palffy-Muhoray
Liquid crystal (LC) elastomers with bent-core side-groups incorporate the properties of bent-core liquid crystals in a flexible and self-supporting polymer network. Bent-core liquid crystal elastomers (BCEs) with uniform alignment were prepared by attaching a reactive bent-core LC to poly(hydrogenmethylsiloxane) and crosslinking with a divinyl crosslinker. Phase behavior studies indicate a nematic phase over a wide temperature range that approaches room temperature, and thermoelastic measurements show that these BCEs can reversibly change their length by more than a factor of two upon heating and cooling. Small-angle X-ray scattering studies reveal multiple, broad low-angle peaks consistent with short-range smectic C order of …
Self-Assembly, Condensation, And Order In Aqueous Lyotropic Chromonic Liquid Crystals Crowded With Additives, Luana Tortora, Heung-Shik Park, Shin-Woong Kang, Victoria Savaryn, Seung-Ho Hong, Konstantine Kaznatcheev, Daniele Finotello, Samuel Sprunt, Satyendra Kumar, Oleg Lavrentovich
Self-Assembly, Condensation, And Order In Aqueous Lyotropic Chromonic Liquid Crystals Crowded With Additives, Luana Tortora, Heung-Shik Park, Shin-Woong Kang, Victoria Savaryn, Seung-Ho Hong, Konstantine Kaznatcheev, Daniele Finotello, Samuel Sprunt, Satyendra Kumar, Oleg Lavrentovich
Satyendra Kumar
Dense multicomponent systems with macromolecules and small solutes attract a broad research interest as they mimic the molecularly crowded cellular interiors. The additives can condense and align the macromolecules, but they do not change the degree of covalentpolymerization. We chose a lyotropic chromonic liquid crystal with reversibly and non-covalently assembled aggregates as a much softer system, reminiscent of “living polymers”, to demonstrate that small neutral and charged additives cause condensation of aggregates with ensuing orientational and positional ordering and nontrivial morphologies of phase separation, such as tactoids and toroids of the nematic and hexagonal columnar phase coexisting with the isotropic …
Light-Driven Molecular Switches With Tetrahedral And Axial Chirality, Lisa Green, Yannian Li, Timothy White, Augustine Urbas, Timothy Bunning, Quan Li
Light-Driven Molecular Switches With Tetrahedral And Axial Chirality, Lisa Green, Yannian Li, Timothy White, Augustine Urbas, Timothy Bunning, Quan Li
Quan Li
Two light-driven molecular switches with tetrahedral and axial chirality were synthesized, which can induce a helical superstructure in an achiral liquid crystal host and dynamically phototune it to achieve reversible reflection color.
Novel Examples Of Achiral Bent-Core Azo Compounds Exhibiting B1 And Anticlinic-Antiferroelectric B2 Mesophases, Veena Prasad, Shin-Woong Kang, Satyendra Kumar
Novel Examples Of Achiral Bent-Core Azo Compounds Exhibiting B1 And Anticlinic-Antiferroelectric B2 Mesophases, Veena Prasad, Shin-Woong Kang, Satyendra Kumar
Satyendra Kumar
The first examples of achiral bent-core molecules consisting of an azo linkage and five aromatic rings exhibiting bent-core mesophases are reported. They exhibit B1 and B2 phases as identified by optical microscopy, differential scanning calorimetry, X-ray diffraction, and electro-optical techniques. The B2 phase of these materials is identified to be the anticlinic–antiferroelectric, SmCAPA phase. The mesophases of these compounds have relatively low transition temperatures and wide temperature ranges. The observation of bent-core phases in azo compounds assumes significance from the fact that the introduction of the –NN– linkage adds a new dimension, namely photochromism, to this field.
Calorimetric Study Of Nematic Prewetting, Xuewu Liu, David W. Allender, D. Finotello
Calorimetric Study Of Nematic Prewetting, Xuewu Liu, David W. Allender, D. Finotello
David W Allender
We report specific-heat measurements for a series of liquid crystals imbedded in a porous cylindrical geometry. Above the nematic-to-isotropic transition and dependent on nematic width (or chain length), the specific heat shows a small peak. In analogy to known ellipsometry results, the peak is believed to be the signature of a nematic prewetting transition.
Relaxation Dynamics Of Rubbed Polystyrene Thin Films, D. M. G. Agra, A. D. Schwab, J-H. Kim, Satyendra Kumar, A. Dhinojwala
Relaxation Dynamics Of Rubbed Polystyrene Thin Films, D. M. G. Agra, A. D. Schwab, J-H. Kim, Satyendra Kumar, A. Dhinojwala
Satyendra Kumar
Optical retardation measurements were used to probe the chain relaxation dynamics in rubbed polystyrene films of varying thicknesses on glass substrates. A model based on Kohlrausch-Williams-Watts relaxation was developed and used to determine the glass transition temperature (Tg) of the films. Results showed reductions of 15–20 K in Tg for thin films of thicknesses comparable to the radius of gyration as well as for cast films rubbed with different strengths. These results provide evidence of a faster relaxation dynamics relative to the polymer-substrate interface for thinner films and enhanced chain mobility at the polymer-air interface.