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Full-Text Articles in Physics

Statistical Mechanics Of Bend Flexoelectricity And The Twist-Bend Phase In Bent-Core Liquid Crystals, Shaikh M. Shamid, Subas Dhakal, Jonathan V. Selinger May 2013

Statistical Mechanics Of Bend Flexoelectricity And The Twist-Bend Phase In Bent-Core Liquid Crystals, Shaikh M. Shamid, Subas Dhakal, Jonathan V. Selinger

Chemical Physics Publications

We develop a Landau theory for bend flexoelectricity in liquid crystals of bent-core molecules. In the nematic phase of the model, the bend flexoelectric coefficient increases as we reduce the temperature toward the nematic to polar phase transition. At this critical point, there is a second-order transition from high-temperature uniform nematic phase to low-temperature nonuniform polar phase composed of twist-bend or splay-bend deformations. To test the predictions of Landau theory, we perform Monte Carlo simulations to find the director and polarization configurations as functions of temperature, applied electric field, and interaction parameters.


Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli Apr 2013

Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli

Chemical Physics Publications

Recently soft fiber mats electrospun from solutions of Barium Titanate (BT) ferroelectric ceramics particles and polylactic acid (PLA) were found to have large (d(33) similar to 1 nm/V) converse piezoelectric signals offering a myriad of applications ranging from active implants to smart textiles. Here, we report direct piezoelectric measurements (electric signals due to mechanical stress) of the BT/PLA composite fiber mats at several BT concentrations. A homemade testing apparatus provided AC stresses in the 50 Hz-1.5 kHz-frequency range. The piezoelectric constant d(33) similar to 0.5 nC/N and the compression modulus Y similar to ...


Characterization Of Cellular Uptake And Toxicity Of Aminosilane-Coated Iron Oxide Nanoparticles With Different Charges In Central Nervous System-Relevant Cell Culture Models, Zhizhi Sun, Vinith Yathindranath, Matthew Worden, James A. Thliveris, Stephanie Chu, Fiona E. Parkinson, Torsten Hegmann, Donald W. Miller Mar 2013

Characterization Of Cellular Uptake And Toxicity Of Aminosilane-Coated Iron Oxide Nanoparticles With Different Charges In Central Nervous System-Relevant Cell Culture Models, Zhizhi Sun, Vinith Yathindranath, Matthew Worden, James A. Thliveris, Stephanie Chu, Fiona E. Parkinson, Torsten Hegmann, Donald W. Miller

Chemical Physics Publications

Background: Aminosilane-coated iron oxide nanoparticles (AmS-IONPs) have been widely used in constructing complex and multifunctional drug delivery systems. However, the biocompatibility and uptake characteristics of AmS-IONPs in central nervous system (CNS)-relevant cells are unknown. The purpose of this study was to determine the effect of surface charge and magnetic field on toxicity and uptake of AmS-IONPs in CNS-relevant cell types.


Surface Induced Phase Separation And Pattern Formation At The Isotropic Interface In Chiral Nematic Liquid Crystals, Rafael S. Zola, L. R. Evangelista, Y.-C Yang, Deng-Ke Yang Jan 2013

Surface Induced Phase Separation And Pattern Formation At The Isotropic Interface In Chiral Nematic Liquid Crystals, Rafael S. Zola, L. R. Evangelista, Y.-C Yang, Deng-Ke Yang

Chemical Physics Publications

We study the pattern formation of a chiral nematic liquid crystal under a wetting transition. In the isotropic-liquid crystal transition, a surface-enhanced effect happens and a thin liquid crystal layer forms at the substrates of the cell. In this confined system, chirality, elastic anisotropy, surface anchoring, and wetting strength interplay. A striped pattern is formed due to the chiral nature of the material and the tilted anchoring at the isotropic boundary. As the wetting layer grows from cooling the sample, first the stripes rotate through a process where dislocation defects are formed. As the wetting layer grows further, the periodicity ...


Simulation Study Of Seemingly Fickian But Heterogeneous Dynamics Of Two Dimensional Colloids, Jeongmin Kim, Chanjoong Kim, Bong June Sung Jan 2013

Simulation Study Of Seemingly Fickian But Heterogeneous Dynamics Of Two Dimensional Colloids, Jeongmin Kim, Chanjoong Kim, Bong June Sung

Chemical Physics Publications

A two-dimensional (2D) solid lacks long-range positional order and is diffusive by means of the cooperative motion of particles. We find from molecular dynamics simulations of hard discs that 2D colloids in solid and hexatic phases show seemingly Fickian but strongly heterogeneous dynamics. Beyond translational relaxation time, the mean-square displacement is linear with time, t, implying that discs would undergo Brownian diffusion and the self-part of the van Hove correlation function [G(s)(r, t)] might be Gaussian. But dynamics is still heterogeneous and G(s)(r, t) is exponential at large r and oscillatory with multiple peaks at intermediate ...


Comment On "The Limits Of Flexoelectricity In Liquid Crystals", Peter Palffy-Muhoray Jan 2013

Comment On "The Limits Of Flexoelectricity In Liquid Crystals", Peter Palffy-Muhoray

Chemical Physics Publications

In their paper, using the principle of energy conservation, F. Castles, S. M. Morris, and H. J. Coles [AIP Advances 1, 032120 (2011)] establish inequalities involving the elastic and dielectric constants and flexoelectric coefficients of liquid crystals. They then argue that recently measured values of flexoelectric coefficients by Harden et al. do not obey these inequalities, hence they violate the principle of energy conservation. In this comment, we point out that in their calculation, Castles et al. use an inappropriate value for an elastic constant, hence their conclusions, predicated on the outcome of this calculation, are not justified. Copyright 2013 ...


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 Jan 2013

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

Chemical Physics Publications

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 ...


Spatial And Orientational Control Of Liquid Crystal Alignment Using A Surface Localized Polymer Layer, Lu Lu, Tatiana Sergan, Vassili Sergan, Philip J. Bos Dec 2012

Spatial And Orientational Control Of Liquid Crystal Alignment Using A Surface Localized Polymer Layer, Lu Lu, Tatiana Sergan, Vassili Sergan, Philip J. Bos

Chemical Physics Publications

We present an alignment method for the surface contacting liquid crystal (LC) director. This method allows complete control of the polar pretilt angle as a function of position in a liquid crystal device, and has the potential of controlling the azimuthal orientation of LC. Important considerations of this method are to form a thin layer of reactive monomers at the LC cell interior surface, and to control the deleterious effects of flow due to polymerization induced concentration gradients. To achieve these, the voltage and frequency of the applied electric field and the UV intensity during the polymerization process are significant.


Mechanism Of Electric-Field-Induced Segregation Of Additives In A Liquid-Crystal Host, Lu Lu, Vassili Sergan, Philip J. Bos Nov 2012

Mechanism Of Electric-Field-Induced Segregation Of Additives In A Liquid-Crystal Host, Lu Lu, Vassili Sergan, Philip J. Bos

Chemical Physics Publications

The mechanism for electric-field-induced segregation of additives, containing a polar group, in a host liquid crystal is proposed. It is shown that the polarity of an applied dc electric field, or the frequency of an ac electric field, strongly influences the segregation of reactive monomers containing an ester group. An explanation of this result is offered based on the association of dissolved ions with polar groups of the reactive monomers. This association is considered to cause these types of additives to drift to the cell surface in the presence of an external electric field. The described mechanism can be applied ...


Deformation Of An Asymmetric Thin Film, Jun Geng, Jonathan V. Selinger Sep 2012

Deformation Of An Asymmetric Thin Film, Jun Geng, Jonathan V. Selinger

Chemical Physics Publications

Experiments have investigated shape changes of polymer films induced by asymmetric swelling by a chemical vapor. Inspired by recent work on the shaping of elastic sheets by non-Euclidean metrics [ Y. Klein, E. Efrati and E. Sharon Science 315 1116 (2007)], we represent the effect of chemical vapors by a change in the target metric tensor. In this problem, unlike that earlier work, the target metric is asymmetric between the two sides of the film. Changing this metric induces a curvature of the film, which may curve into a partial cylinder or a partial sphere. We calculate the elastic energy for ...


Direct Observation Of Smectic Layers In Thermotropic Liquid Crystals, C. Zhang, M. Gao, Wolfgang Weissflog, Ute Baumeister, Samuel N. Sprunt, Jim T. Gleeson, Antal Jákli Sep 2012

Direct Observation Of Smectic Layers In Thermotropic Liquid Crystals, C. Zhang, M. Gao, Wolfgang Weissflog, Ute Baumeister, Samuel N. Sprunt, Jim T. Gleeson, Antal Jákli

Chemical Physics Publications

We demonstrate subnanometer resolution cryo-TEM imaging of smectic layers in the smectic and nematic phases of two bent-core liquid crystals. Our results show perfect periodicity over several hundred layers in the smectic phase and also provide the first direct evidence of smectic clusters on length scales of 30-50 nm in a nematic liquid crystal. The results are corroborated with small angle x-ray scattering measurements. The observation of smectic clusters in the nematic phase is of special interest in bent-core liquid crystals, where the smectic clusters are stable over wide temperature ranges, in contrast to the well-known pretransitional "cybotactic" clusters that ...


Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson Aug 2012

Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson

Chemical Physics Publications

We report on a series of measurements on the microscopic structure and the magneto-optical properties of a calamitic liquid crystalline compound in its nematic phase. Structural studies show the existence of short-range, tilted smectic order consistent with pretransitional effects above an underlying smectic phase. Concomitantly, magneto-optical results exhibit the existence of an optic axis not collinear with the uniaxial director. This apparent biaxial nature is discussed within the context of coupling between the tensor nematic and the smectic order parameters.


Light Scattering From Liquid Crystal Director Fluctuations In Steady Magnetic Fields Up To 25 Tesla, Pavan K. Challa, O. Curtiss, J. C. Williams, Robert J. Twieg, J. Toth, S. Mcgill, Jim T. Gleeson, Antal Jakli, Samuel N. Sprunt Jul 2012

Light Scattering From Liquid Crystal Director Fluctuations In Steady Magnetic Fields Up To 25 Tesla, Pavan K. Challa, O. Curtiss, J. C. Williams, Robert J. Twieg, J. Toth, S. Mcgill, Jim T. Gleeson, Antal Jakli, Samuel N. Sprunt

Chemical Physics Publications

We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (Q(alpha beta)B(alpha)B(beta)) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may ...


Elasticity Of Lyotropic Chromonic Liquid Crystals Probed By Director Reorientation In A Magnetic Field, Shuang Zhou, Yuriy A. Nastishin, M. M. Omelchenko, L. Tortora, V. G. Nazarenko, O. P. Boiko, T. Ostapenko, T. Hu, C. C. Almasan, Jim T. Gleeson, Oleg Lavrentovich Jul 2012

Elasticity Of Lyotropic Chromonic Liquid Crystals Probed By Director Reorientation In A Magnetic Field, Shuang Zhou, Yuriy A. Nastishin, M. M. Omelchenko, L. Tortora, V. G. Nazarenko, O. P. Boiko, T. Ostapenko, T. Hu, C. C. Almasan, Jim T. Gleeson, Oleg Lavrentovich

Chemical Physics Publications

Using a magnetic Frederiks transition technique, we measure the temperature and concentration dependences of splay K1, twistK2, and bend K3 elastic constants for the lyotropic chromonic liquid crystal sunset yellow formed through noncovalent reversible aggregation of organic molecules in water. K1 and K3 are comparable to each other and are an order of magnitude higher thanK2. At higher concentrations and lower temperatures, K1 and the ratios K1/K3 and K1/K2 increase, which is attributed to elongation of self-assembled lyotropic chromonic liquid crystal aggregates, a feature not ...


Polarization Conversion With Elliptical Patch Nanoantennas, Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, Qi-Huo Wei Jul 2012

Polarization Conversion With Elliptical Patch Nanoantennas, Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, Qi-Huo Wei

Chemical Physics Publications

In this paper, we demonstrate arrays of optical patch nanoantennas can convert light polarization through reflection. By breaking the azimuthal symmetry, elliptical plasmonic patch nanoantennas exhibit both even and odd cavity modes, which can be expressed by Mathieu functions. It is shown that by properly orienting the incident polarization, a linearly polarized light in resonance with one cavity mode can be converted into an elliptical or circular polarization after reflection. Since the major cavity modes can be excited at all incident angles, the polarization conversion by these elliptical patch nanoantennas can be realized with wide range of incident angles.


Pattern-Stabilized Decorated Polar Liquid-Crystal Fibers, Alexey Eremin, Ulrike Kornek, Stephan Stern, Ralf Stannarius, Fumito Araoka, Hideo Takezoe, Hajnalka Nadasi, Wolfgang Weissflog, Antal Jakli Jul 2012

Pattern-Stabilized Decorated Polar Liquid-Crystal Fibers, Alexey Eremin, Ulrike Kornek, Stephan Stern, Ralf Stannarius, Fumito Araoka, Hideo Takezoe, Hajnalka Nadasi, Wolfgang Weissflog, Antal Jakli

Chemical Physics Publications

Geometric frustration gives rise to new fundamental phenomena and is known to yield the formation of exotic states of matter, such as incommensurate crystals, modulated liquid-crystalline phases, and phases stabilized by defects. In this Letter, we present a detailed study of polar structure of freely suspended fluid filaments in a polarization modulated liquid-crystal phase. We show that a periodic pattern of polarization-splay stripes separated by defect boundaries and decorating smectic layers can stabilize the structure of fluid fibers against the Rayleigh-Plateau instability. The instability is suppressed by the resistance of the defect structure to a radial compression of the cylindrical ...


Photoisomerization-Controlled Phase Segregation In A Submicron Confined Azonematic Liquid Crystal, B. Zupančič, S. Diez-Berart, D. Finotello, Oleg Lavrentovich, V. Zalar Jun 2012

Photoisomerization-Controlled Phase Segregation In A Submicron Confined Azonematic Liquid Crystal, B. Zupančič, S. Diez-Berart, D. Finotello, Oleg Lavrentovich, V. Zalar

Chemical Physics Publications

Deuteron nuclear magnetic resonance is used to study the phase segregation behavior of photoisomerizable liquid crystal diheptylazobenzene (7AB) confined into cylindrical pores of Anopore membranes. It is demonstrated that the concentration of both components in a binary trans-7AB and cis-7AB mixture can be controlled dynamically using UV-illumination stimulated trans-to-cisphotoisomerization and thermally induced cis-to-trans backisomerization. The so far elusive temperature-concentration phase diagram of such system is determined by comparative analysis of the behavior in bulk, thin-planar, and Anopore-confining geometry.


The Effect Of Salt On Ion Adsorption On A Siox Alignment Film And Reduced Conductivity Of A Liquid Crystal Host, Yi Huang, Achintya Bhowmik, Philip J. Bos Jun 2012

The Effect Of Salt On Ion Adsorption On A Siox Alignment Film And Reduced Conductivity Of A Liquid Crystal Host, Yi Huang, Achintya Bhowmik, Philip J. Bos

Chemical Physics Publications

It is shown that the addition of salt to liquid crystal cells, using a SiOx alignment layer, can actually reduce the ion concentration. This seeming contradiction may be explained by the ability of salt to complex with water and to aid the drying of the liquid crystal material. The results show a pathway to purifying liquid crystal devices to the extent needed for low-power low-refresh rate displays for e-book applications.


Dielectric Technique To Measure The Twist Elastic Constant Of Liquid Crystals: The Case Of A Bent-Core Material, Peter Salamon, Nandor Éber, J. Seltmann, M. Lehmann, Jim T. Gleeson, Samuel N. Sprunt, Antal Jákli Jun 2012

Dielectric Technique To Measure The Twist Elastic Constant Of Liquid Crystals: The Case Of A Bent-Core Material, Peter Salamon, Nandor Éber, J. Seltmann, M. Lehmann, Jim T. Gleeson, Samuel N. Sprunt, Antal Jákli

Chemical Physics Publications

The effect of director pretilt on the twist magnetic Freedericksz transition of nematics was investigated in a planar cell. The director configuration was calculated as a function of magnetic inductance. The dielectric and optical response of the nematic liquid crystal was numerically modeled. A dielectric measurement method for determining the elastic constant K-22 is presented. The influence of the conditions for the Mauguin effect is discussed. The theoretical predictions were confirmed by our experiments. Experimental data for all elastic constants of a bent-core nematic material are presented and discussed.


Azimuthal Dependence Of Switching Field Strength For Nematic Liquid Crystal Bistability On Patterned Alignment Layers, Jun-Ichi Niitsuma, Makoto Yoneya, Hiroshi Yokoyama May 2012

Azimuthal Dependence Of Switching Field Strength For Nematic Liquid Crystal Bistability On Patterned Alignment Layers, Jun-Ichi Niitsuma, Makoto Yoneya, Hiroshi Yokoyama

Chemical Physics Publications

We investigate the azimuthal dependence of the switching field strength for nematic liquid crystal bistability on patterned alignment layers to determine the validity of a switching theory proposed by Kim et al. [Appl. Phys. Lett. 78, 3055 (2001)] and to evaluate higher-order azimuthal anchoring coefficients. Director behavior during switching is described in detail for general azimuthal directions of an applied electric field and the experimental results are explained on the basis of the theory. We obtain azimuthal anchoring coefficients up to the second higher-order term in an expansion of the anchoring energy function. Detailed analysis of the director behavior reveals ...


Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli Feb 2012

Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli

Chemical Physics Publications

We report the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA). These fibers form mats that have two orders of magnitude larger piezoelectric constant per weight than single crystal barium titanate films. We propose that the observed apparent piezoelectricity results from the electrospinning induced polar alignment of the ferroelectric particles that pole the fibers similar to ferroelectret polymer foams that are poled by corona discharge. Due to the biocompatibility of PLA that encases the ferroelectric particles, these mats can be used in biological applications such as bio-sensors, artificial ...


Surface Wrinkling In Liquid Crystal Elastomers, Aditya Agrawal, Paul Luchette, Peter Palffy-Muhoray, Sibani Lisa Biswal, Walter G. Chapman, Rafael Verduzco Jan 2012

Surface Wrinkling In Liquid Crystal Elastomers, Aditya Agrawal, Paul Luchette, Peter Palffy-Muhoray, Sibani Lisa Biswal, Walter G. Chapman, Rafael Verduzco

Chemical Physics Publications

Structured surfaces give rise to novel and potentially useful properties such as controllable wettability and structural colour. Here, we demonstrate structured surfaces via reversible surface wrinkling in liquid crystal elastomers (LCEs). A thin polymer film deposited on top of a shape-responsive LCE exhibits a reversible, periodic surface wrinkling pattern in response to temperature changes. The orientation of the wrinkles depends on the orientation of the nematic director and the temperature at which the bilayer is prepared, and the wrinkles can be re-oriented in a single sample by heating or cooling the sample above or below the preparation temperature. We show ...


Alignment Layers With Variable Anchoring Strengths From Polyvinyl Alcohol, Yue Cui, Rafael S. Zola, Young-Cheol Yang, Deng-Ke Yang Jan 2012

Alignment Layers With Variable Anchoring Strengths From Polyvinyl Alcohol, Yue Cui, Rafael S. Zola, Young-Cheol Yang, Deng-Ke Yang

Chemical Physics Publications

In the study of polyvinyl alcohol (PVA) alignment layers for liquid crystal devices, we found that the anchoring strength can be greatly varied by changing the alignment film thickness. Both the polar and azimuthal anchoring strengths increased with increasing film thickness; however, they had different film thickness dependences. It was also noticed that the quartic term in the expansion of the Rapini-Papoular anchoring energy was important for describing the polar anchoring. In the experiment, solid PVA was dissolved in a thinner and spin-coated on glass substrates to create alignment layers. The substrates were assembled to make electrically-controlled birefringence liquid crystal ...


Note: Automated Maskless Micro-Multidomain Photoalignment, Christopher Culbreath, Nikolaus Glazar, Hiroshi Yokoyama Dec 2011

Note: Automated Maskless Micro-Multidomain Photoalignment, Christopher Culbreath, Nikolaus Glazar, Hiroshi Yokoyama

Chemical Physics Publications

We present a fully automated maskless exposure system for the fabrication of microscopic orientational surface alignment patterns. The maskless system allows us to fabricate arbitrary surface patterns over a 2 mm × 2 mm area with a resolution of 2.2 μm. A confocal autofocus system insures accurate and repeatable focus. Microscopic orientational surface patterns have been demonstrated to exhibit a variety of novel functionalities, such as surface alignment multi-stability.


Maier-Saupe-Type Theory Of Ferroelectric Nanoparticles In Nematic Liquid Crystals, Lena M. Lopatina, Jonathan V. Selinger Oct 2011

Maier-Saupe-Type Theory Of Ferroelectric Nanoparticles In Nematic Liquid Crystals, Lena M. Lopatina, Jonathan V. Selinger

Chemical Physics Publications

Several experiments have reported that ferroelectric nanoparticles have drastic effects on nematic liquid crystals-increasing the isotropic-nematic transition temperature by about 5 K, and greatly increasing the sensitivity to applied electric fields. In a recent paper [Lopatina and Selinger, Phys. Rev. Lett. 102, 197802 (2009)], we modeled these effects through a Landau theory, based on coupled orientational order parameters for the liquid crystal and the nanoparticles. This model has one important limitation: Like all Landau theories, it involves an expansion of the free energy in powers of the order parameters, and hence it overestimates the order parameters that occur in the ...


Magneto-Optical Technique For Detecting The Biaxial Nematic Phase, T. Ostapenko, C. Zhang, Samuel N. Sprunt, Antal Jákli, Jim T. Gleeson Aug 2011

Magneto-Optical Technique For Detecting The Biaxial Nematic Phase, T. Ostapenko, C. Zhang, Samuel N. Sprunt, Antal Jákli, Jim T. Gleeson

Chemical Physics Publications

The existence of the elusive biaxial phase has been the subject of much discussion since it was predicted by Freiser in 1970. More recently, there have been numerous attempts to find a thermotropic liquid crystal that exhibits a biaxial phase and with this, conflicting reports about whether such a phase has been positively identified in bent-core liquid crystals. One reason for the discrepancy is that there is currently no way to rule out surface effects or anchoring transitions, both of which may give a false positive identification of a uniaxial-biaxial nematic transition. We have developed a technique that uses a ...


Solar To Electrical Conversion Via Liquid Crystal Elastomers, T. Hiscock, M. Warner, Peter Palffy-Muhoray Jun 2011

Solar To Electrical Conversion Via Liquid Crystal Elastomers, T. Hiscock, M. Warner, Peter Palffy-Muhoray

Chemical Physics Publications

We have constructed a hypothetical charge pump which converts solar energy into DC electricity. The output is generated by cyclic changes in the capacitance of a circuit, which transfers charge from a low to a high voltage. The electric field across the capacitor must be of the order of 10(8)Vm(-1) to compete with efficiencies of photovoltaics. We have modeled the output using a liquid crystal elastomer as the working substance. Efficiencies of 1 - 4% are obtained, and are enhanced by careful choices in the capacitor geometries and the operating voltages of the charge pump. (C) 2011 American ...


Nanostructures Of Liquid Crystal Phases In Mixtures Of Bent-Core And Rod-Shaped Molecules, Seung Ho Hong, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Jun 2011

Nanostructures Of Liquid Crystal Phases In Mixtures Of Bent-Core And Rod-Shaped Molecules, Seung Ho Hong, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

We report small angle x-ray scattering (SAXS) studies of isotropic, nematic, and smectic mesophases formed by binary mixtures of bent-core (BC) and rod-shaped (RS) molecules. While optical studies indicate that the components are fully miscible, SAXS reveals fascinating structures that are consistent with segregation on a nanoscopic scale. We find that tilted smectic clusters, which have been previously reported in both the nematic and isotropic states of the pure BC materials, are also present in mixtures with up to 50 wt% of the RS compound; this is consistent with previous dielectric and flexoelectric studies on such mixtures. Unexpectedly in this ...


One Order Parameter Tensor Mean Field Theory For Biaxial Liquid Crystals, Xiaoyu Zheng, Peter Palffy-Muhoray Mar 2011

One Order Parameter Tensor Mean Field Theory For Biaxial Liquid Crystals, Xiaoyu Zheng, Peter Palffy-Muhoray

Chemical Physics Publications

In this paper, we present a simple one tensor mean field model of biaxial nematic liquid crystals. The salient feature of our approach is that material parameters appear explicitly in the order parameter tensor. We construct the free energy from a mean field potential based on anisotropic dispersion interactions, identify the order parameter tensor and its elements, and obtain self-consistent equations, which are then solved numerically. The results are illustrated in a 3D ternary phase diagram. The phase behavior can be simply related to molecular parameters. The results may be useful for designing molecules that show a thermotropic biaxial phase.


Effect Of Trans-Cis Photoisomerization On Phase Equilibria And Phase Transition Of Liquid-Crystalline Azobenzene Chromophore And Its Blends With Reactive Mesogenic Diacrylate, Namil Kim, Quan Li, Thein Kyu Mar 2011

Effect Of Trans-Cis Photoisomerization On Phase Equilibria And Phase Transition Of Liquid-Crystalline Azobenzene Chromophore And Its Blends With Reactive Mesogenic Diacrylate, Namil Kim, Quan Li, Thein Kyu

Chemical Physics Publications

Photoisomerization-induced phase transition of neat liquid-crystalline azobenzene chromophore (LCAC) and its effect on phase diagrams of its mixtures with reactive mesogenic diacrylate monomer (RM257) have been investigated experimentally and theoretically. Upon irradiation with ultraviolet light, the nematic phase of LCAC transformed to isotropic, while the crystal phase showed corrugated textures on the surface (i.e., ripples). The phase-transition temperatures and corresponding morphologies of the blends have been investigated by means of differential scanning calorimetry and optical microscopy. A theoretical phase diagram of a binary nematic and crystalline system was constructed by self-consistently solving the combined free energies of Flory-Huggins, Maier-Saupe ...