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Articles 1 - 18 of 18
Full-Text Articles in Physical Sciences and Mathematics
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 …
Nonlinear Schrodinger Equation In Nematic Liquid Crystals, Peter Palffy-Muhoray, J. A. Reyes
Nonlinear Schrodinger Equation In Nematic Liquid Crystals, Peter Palffy-Muhoray, J. A. Reyes
Peter Palffy-Muhoray
We derive the amplitude equation, in the weakly nonlinear regime, for an optical wave packet that propagates in an initially undistorted nematic liquid crystal. By using the dyad representation Q(ij), we find the retarded and nonlocal equation for the nematic configuration and solve it in Fourier space. This allows us to calculate the amplitude dependent dispersion relation for a nematic liquid crystal in a given initial undistorted stationary state. We consider a linearly polarized wave packet that travels along the principal axis of the nematic dielectric tensor. We find a nonlinear Schrodinger equation for the amplitude, which includes an additional …
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 …
Nonphotochemical Laser-Induced Nucleation Of Nematic Phase And Alignment Of Nematic Director From A Supercooled Thermotropic Liquid Crystal, Xiaoying Sun, Bruce A. Garetz, Michele F. Moreira, Peter Palffy-Muhoray
Nonphotochemical Laser-Induced Nucleation Of Nematic Phase And Alignment Of Nematic Director From A Supercooled Thermotropic Liquid Crystal, Xiaoying Sun, Bruce A. Garetz, Michele F. Moreira, Peter Palffy-Muhoray
Peter Palffy-Muhoray
A nonphotochemical laser-induced phase transition was studied in a supercooled 4′‐n-pentyl-4-cyanobiphenyl (5CB, also referred to as PCB and K15) liquid crystal, using linearly polarized 45 ps light pulses at a wavelength of 532 nm. The laser induced nucleation from the metastable supercooled isotropic phase to the nematic phase during slow cooling (0.001 °C∕min) and high light intensity (3.9 MW∕cm2). The resulting nematic director tended to be aligned along the direction of the plane of polarization of the light. At the intensities used, there is no observable laser-induced realignment of the director once the sample is in the nematic …
Cholesteric Liquid-Crystal Laser As An Optic Fiber-Based Temperature Sensor, M. F. Moreira, I.C.S. Carvalho, W. Cao, C. Bailey, Bahman Taheri, Peter Palffy-Muhoray
Cholesteric Liquid-Crystal Laser As An Optic Fiber-Based Temperature Sensor, M. F. Moreira, I.C.S. Carvalho, W. Cao, C. Bailey, Bahman Taheri, Peter Palffy-Muhoray
Peter Palffy-Muhoray
In this work, we have studied the temperature dependence of a cholesteric liquid-crystal laser coupled to an optical fiber, with a view towards optical fiber sensor applications. To stabilize the laser emission, we developed a procedure to align the liquid crystal placed in the fiber. Unexpected oscillations in the laser emission were observed as the temperature was varied, which can be understood in terms of the competition between bulk and surface anchoring torques. (C) 2004 American Institute of Physics.
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 …
Analytical Solution Of Maxwell's Equations In Lossy And Optically Active Crystals, Haijun Yuan, E. Weinan, Peter Palffy-Muhoray
Analytical Solution Of Maxwell's Equations In Lossy And Optically Active Crystals, Haijun Yuan, E. Weinan, Peter Palffy-Muhoray
Peter Palffy-Muhoray
Analytical solution of Maxwell's equations is obtained for general linear optical materials: lossy and optically active crystals. Explicit expressions are obtained for the dispersion relation and the propagating eigenmodes. In general, four rather than two distinct modes are present. The results are useful in describing light propagation in optically complex media.
Modeling The Mechanisms Of The Photomechanical Response Of A Nematic Liquid Crystal Elastomer, Nathan J. Dawson, Mark G. Kuzyk, Jeremy Neal, Paul Luchette, Peter Palffy-Muhoray
Modeling The Mechanisms Of The Photomechanical Response Of A Nematic Liquid Crystal Elastomer, Nathan J. Dawson, Mark G. Kuzyk, Jeremy Neal, Paul Luchette, Peter Palffy-Muhoray
Peter Palffy-Muhoray
Recent studies of azo-dye-doped liquid crystal elastomers show a strong photomechanical response. We report on models that predict experimental results that suggest photothermal heating is the dominant mechanism in a planar constrained geometry. We compare our models with experiments to determine key material parameters, which are used to predict the dynamical response as a function of intensity. We show that a local strain from photothermal heating and a nonlocal strain from thermal diffusion is responsible for the observed length changes over time. This work both elucidates the fundamental mechanisms and provides input for the design of photomechanical optical devices, which …
Experimental Studies Of The Mechanisms Of Photomechanical Effects In A Nematic Liquid Crystal Elastomer, Nathan J. Dawson, Mark G. Kuzyk, Jeremy Neal, Paul Luchette, Peter Palffy-Muhoray
Experimental Studies Of The Mechanisms Of Photomechanical Effects In A Nematic Liquid Crystal Elastomer, Nathan J. Dawson, Mark G. Kuzyk, Jeremy Neal, Paul Luchette, Peter Palffy-Muhoray
Peter Palffy-Muhoray
Azo-dye-doped liquid crystal elastomers (LCEs) are known to show a strong photomechanical response. We report on experiments that suggest that photothermal heating is the underlying mechanism in surface-constrained geometry. In particular, we use optical interferometry to probe the length change of the material and direct temperature measurements to determine heating. LCEs with various dopants and optical density were used to study the individual mechanisms. In the high dye-doped limit, most of the light is absorbed near the entry surface, which causes a local strain from photothermal heating and a nonlocal strain from thermal diffusion. The results of our research on …
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 …
Director Dynamics In Liquid-Crystal Physical Gels, Rafael Verduzco, Neal R. Scruggs, Samuel Sprunt, Peter Palffy-Muhoray, Julia A. Kornfield
Director Dynamics In Liquid-Crystal Physical Gels, Rafael Verduzco, Neal R. Scruggs, Samuel Sprunt, Peter Palffy-Muhoray, Julia A. Kornfield
Peter Palffy-Muhoray
Nematic liquid- crystal (LC) elastomers and gels have a rubbery polymer network coupled to the nematic director. While LC elastomers show a single, non- hydrodynamic relaxation mode, dynamic light- scattering studies of self- assembled liquid- crystal gels reveal orientational fluctuations that relax over a broad time scale. At short times, the relaxation dynamics exhibit hydrodynamic behavior. In contrast, the relaxation dynamics at long times are non-hydrodynamic, highly anisotropic, and increase in amplitude at small scattering angles. We argue that the slower dynamics arise from coupling between the director and the physically associated network, which prevents director orientational fluctuations from decaying …
A Dunking Bird Of The Second Kind, Nadine Abraham, Peter Palffy-Muhoray
A Dunking Bird Of The Second Kind, Nadine Abraham, Peter Palffy-Muhoray
Peter Palffy-Muhoray
The conventional dunking bird is a heat engine that relies on the temperature difference between the head and the tail of the bird for its operation. We describe a new type of dunking bird that is not a heat engine, but one that directly uses the chemical potential difference between liquid water and its vapor.
Thermal-Lens Model Compared With The Sheik-Bahae Formalism In Interpreting Z-Scan Experiments On Lyotropic Liquid Crystals, Fabio Luiz Sant'anna Cuppo, Antonio Martins Figueiredo Neto, Sergio Leonardo Gomez, Peter Palffy-Muhoray
Thermal-Lens Model Compared With The Sheik-Bahae Formalism In Interpreting Z-Scan Experiments On Lyotropic Liquid Crystals, Fabio Luiz Sant'anna Cuppo, Antonio Martins Figueiredo Neto, Sergio Leonardo Gomez, Peter Palffy-Muhoray
Peter Palffy-Muhoray
We carried out Z-scan measurements on lyotropic liquid crystals and on lyotropic liquid crystals doped with ferrofluid. In these experiments, the sample is translated through the focal region of a focused Gaussian laser beam. The dependence of the far-field intensity on sample position due to intensity-dependent optical nonlinearities has been analyzed on the basis of the thermal-lens model of Gordon et al. and the Gaussian decomposition analysis of Sheik-Bahae et al. The thermal-lens model is nonlocal in space and time, whereas the Gaussian decomposition is predicated on a strictly local response. We compare the goodness of fit of the predictions …
Three-Dimensional Dye Distribution In Photo-Oriented Liquid-Crystal Alignment Layers, S. Bardon, D. Coleman, N. A. Clark, T. Kosa, H. Yuan, Peter Palffy-Muhoray
Three-Dimensional Dye Distribution In Photo-Oriented Liquid-Crystal Alignment Layers, S. Bardon, D. Coleman, N. A. Clark, T. Kosa, H. Yuan, Peter Palffy-Muhoray
Peter Palffy-Muhoray
The three-dimensional optical anisotropy of photo-buffed dye-doped polymer films and the resulting orientation imparted to a liquid crystal in contact are probed using total internal reflection. Although the linearly polarized writing light generates a uniaxial distribution of dye molecules, the polymer films are biaxial, a result of symmetry breaking by the film surface.
The Single Particle Potential In Mean-Field Theory, Peter Palffy-Muhoray
The Single Particle Potential In Mean-Field Theory, Peter Palffy-Muhoray
Peter Palffy-Muhoray
The problem of determining the single particle energy in a mean-field description of interacting particles is considered. It is shown that the single particle energy must satisfy two consistency conditions, and a general procedure for obtaining the single particle energy from the pair energy is proposed. Interacting dipolar systems are examined, current approaches in the literature are discussed, and the usefulness of the proposed method is demonstrated.
Comment On "A Check Of Prigogine's Theorem Of Minimum Entropy Production In A Rod In A Nonequilibrium Stationary State", Peter Palffy-Muhoray
Comment On "A Check Of Prigogine's Theorem Of Minimum Entropy Production In A Rod In A Nonequilibrium Stationary State", Peter Palffy-Muhoray
Peter Palffy-Muhoray
No abstract provided.
Optically Induced Periodic Structures In Smectic-C Liquid Crystals, Antal Jákli, A. Vajda, E. Benkler, Janossy, Peter Palffy-Muhoray
Optically Induced Periodic Structures In Smectic-C Liquid Crystals, Antal Jákli, A. Vajda, E. Benkler, Janossy, Peter Palffy-Muhoray
Peter Palffy-Muhoray
We explore periodic structures of smectic-C (SmC) liquid crystals, induced optically by a polarization grating. The studied cells contain a passive surface of rubbed polyimide and an active photosensitive substrate of ate-dye doped polyimide. In a nematic phase the director field can be periodic independent of the angle between the grating vector and the rubbing direction. In the SmA phase periodic structure can be induced only by layer undulations. The SmC behaves similarly to the nematic phase, but the director can rotate only on a cone, which results in a more complex geometry. The periodic pattern is superimposed with four …
Mirage Mirror On The Wall, T. Kosa, Peter Palffy-Muhoray
Mirage Mirror On The Wall, T. Kosa, Peter Palffy-Muhoray
Peter Palffy-Muhoray
We discuss mirages formed near a sun-heated wall, and consider the underlying physics. The temperature and refractive index variations in air near the wall are estimated, and a simple approximate picture of ray propagation is presented. Estimates of the thermal decay length and ray curvature are compared with experimental observations.