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Experimental Studies of the Mechanisms of Photomechanical Effects in a Nematic Liquid Crystal Elastomer in a Photomechanical Optical Device Geometry  [PDF]
Nathan J. Dawson,Mark G. Kuzyk,Jeremy Neal,Paul Luchette,Peter Palffy-Muhoray
Physics , 2011, DOI: 10.1364/JOSAB.28.001916
Abstract: 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 the microscopic mechanisms of the photomechanical response can be applied to designing photomechanical materials for actuating/sensing devices, the potential basis of smart structures.
Modeling the Mechanisms of the Photomechanical Response of a Nematic Liquid Crystal Elastomer  [PDF]
Nathan J. Dawson,Mark G. Kuzyk,Jeremy Neal,Paul Luchette,Peter Palffy-Muhoray
Physics , 2011, DOI: 10.1364/JOSAB.28.002134
Abstract: 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 have been shown to have the appropriate properties for making smart materials.
Synthesis and Characterization of Liquid Crystal Elastomer  [PDF]
Rita A. Gharde, Santosh A. Mani, Suman Lal, Samriti Khosla, S. K. Tripathi
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.66056
Abstract: The thermal and mechanical properties of Liquid Crystal Elastomers (LCEs) were characterized using various techniques for understanding of their physical behavior. The material used for investigation was synthesized by us, using Finklemann procedure, with proper cross linking density in nematic phase. The material is found to have unique coupling between anisotropicorder of liquid crystal component and elasticity of polymer network. The chemical structures were confirmed by Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM). Fabry Perot Scattering Studies (FPSS), Thermo gravimetric Analysis (TGA) and Differential Scanning Calorimatory (DSC) were used to study thermal properties. The mechanical properties were studied using force sensor. Our investigation shows that this synthesized Liquid Crystal Elastomer has ability of spontaneous change as a function of temperature and mechanical force, which shows it as a unique class of soft material.
Critical Field Strength in an Electroclinic Liquid Crystal Elastomer  [PDF]
Christopher M. Spillmann,Amit V. Kapur,Frank W. Bentrem,Jawad Naciri,Banahalli R. Ratna
Physics , 2010, DOI: 10.1103/PhysRevLett.104.227802
Abstract: We elucidate the polymer dynamics of a liquid crystal elastomer based on the time-dependent response of the pendent liquid crystal mesogens. The molecular tilt and switching time of mesogens are analyzed as a function of temperature and cross-linking density upon application of an electric field. We observe an unexpected maximum in the switching time of the liquid crystal mesogens at intermediate field strength. Analysis of the molecular tilt over multiple time regimes correlates the maximum response time with a transition to entangled polymer dynamics at a critical field strength.
Photomechanical Response of Composite Structures Built from Azobenzene Liquid Crystal Polymer Networks  [PDF]
Kyung Min Lee,Timothy J. White
Polymers , 2011, DOI: 10.3390/polym3031447
Abstract: Optically directed shape adaptive responses have been sought after for many decades in photoresponsive polymeric materials. A number of recent examinations have elucidated elucidated the unique opportunities of photomechanical responses realized in azobenzene-functionalized liquid crystalline polymer networks (both elastomers and glasses). This work summarizes and contrasts the photomechanical response of glassy polydomain, monodomain, and twisted nematic azo-LCN materials to blue-green irradiation. Building from this summary, the combinatorial photomechanical response observed upon irradiation of composite cantilevers is examined. Large scale shape adaptations are realized, with novel responses that may be of potential use in future employment of these materials in actuation.
Numerical Study of Liquid Crystal Elastomer Using Mixed Finite Element Method  [PDF]
Chong Luo,Maria-Carme Calderer
Mathematics , 2009,
Abstract: We aimed to use finite element method to simulate the unique behaviors of liquid crystal elastomer, such as semi-soft elasticity, stripe domain instabilities etc. We started from an energy functional with the 2D Bladon-Warner-Terentjev stored energy of elastomer, the Oseen-Frank energy of liquid crystals, plus the penalty terms for the incompressibility constraint on the displacement, and the unity constraint on the director. Then we applied variational principles to get the differential equations. Next we used mixed finite element method to do the numerical simulation. The existence, uniqueness, well-posedness and convergence of the numerical methods were investigated. The semi-soft elasticity was observed, and can be related to the rotation of the directors. The stripe domain phenomenon, however, wasn't observed. This might due to the relative coarse mesh we have used.
Modelling nematohydrodynamics in liquid crystal devices  [PDF]
Geza Toth,Colin Denniston,J. M. Yeomans
Physics , 2002, DOI: 10.1016/S0010-4655(02)00196-0
Abstract: We formulate a lattice Boltzmann algorithm which solves the hydrodynamic equations of motion for nematic liquid crystals. The applicability of the approach is demonstrated by presenting results for two liquid crystal devices where flow has an important role to play in the switching.
Inverse Design of Photonic Crystal Devices  [PDF]
Andreas Hakansson,Jose Sanchez-Dehesa,Lorenzo Sanchis
Physics , 2005,
Abstract: This work deals with the inverse design in the field of photonic crystal based devices. Here an inverse method containing a fast and accurate simulation method integrated with a competent optimization method is presented. Two designs yielded from this conjunction of multiple scattering theory with a genetic algorithm is analyzed. The potential of this approach is illustrated by designing a lens that has a very low F-number (F=0.47) and a conversion ratio of 11:1. We have also designed a coupler device that introduces the light from an optical fiber into a PC based wave-guide with a predicted coupling efficiency that exceeds 87%.
Phase transition in liquid crystal elastomer - a Monte Carlo study employing non-Boltzmann sampling  [PDF]
D. Jayasri,N. Satyavathi,V. S. S. Sastry,K. P. N. Murthy
Physics , 2006,
Abstract: We investigate Isotropic - Nematic transition in liquid crystal elastomers employing non-Boltzmann Monte Carlo techniques. We consider a lattice model of a liquid elastomer and Selinger-Jeon-Ratna Hamiltonian which accounts for homogeneous/inhomogeneous interactions among liquid crystalline units, interaction of local nematics with global strain, and with inhomogeneous external fields and stress. We find that when the local director is coupled strongly to the global strain the transition is strongly first order; the transition softens when the coupling becomes weaker. Also the transition temperature decreases with decrease of coupling strength. Besides we find that the nematic order scales nonlinearly with global strain especially for strong coupling and at low temperatures.
Propagation of Light in Photonic Crystal Fibre Devices  [PDF]
Ali Dabirian,Mahmood Akbari,Niels Asger Mortensen
Physics , 2005, DOI: 10.1088/1464-4258/7/11/008
Abstract: We describe a semi-analytical approach for three-dimensional analysis of photonic crystal fibre devices. The approach relies on modal transmission-line theory. We offer two examples illustrating the utilization of this approach in photonic crystal fibres: the verification of the coupling action in a photonic crystal fibre coupler and the modal reflectivity in a photonic crystal fibre distributed Bragg reflector.
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