Dynamics of Director Fluctuations in Confined Liquid Crystals
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0899-N07-11.1
Dynamics of Director Fluctuations in Confined Liquid Crystals Sarmistha Basu, Edwin Arroyo, Fouad Aliev Department of Physics, University of Puerto Rico, San Juan, PR 00931-3343, USA ABSTRACT Dynamic light scattering was applied to study the influence of randomness, boundary conditions (planar-axial and homeotropic-radial) and layer thickness (at nanoscale) of 5CB and 8CB confined to cylindrical pores and filled with Aerosil particles on relaxation of director orientational fluctuations. For confined 8CB in the nematic phase two well-defined relaxation processes were observed for both axial and radial orientations of the liquid crystal. The first process is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation process (with slower relaxation time than the first one) is most likely due to the fluctuations in layers nearest the wall surface. The separation between the first and the second (slow) processes is clearer for thinner layers and the amplitude of the slow process is greater for thinner layers. This suggests that the slow process is surface related relaxation. The mode due to relaxation of fluctuations of director orientation in the vicinity of the surface of Aerosil particles was observed in filled liquid crystals as well. INTRODUCTION Heterogeneous systems based on liquid crystals (LC), such as liquid crystals dispersed in a polymer matrix [1] or in inorganic porous matrices [2] are materials extremely important for applications as well as fundamental physics of confined systems. Another system that has key similarities (as well as differences) with systems of liquid crystal confined in rigid and solid porous matrices is liquid crystal filled with Aerosil particles, which form a stable threedimensional network dividing the liquid crystal into LC domains with a linear size of approximately 250 nm [3]. Such a network creates a quenched disorder in the liquid crystal. These systems – confined and filled liquid crystals - are anisotropic and heterogeneous materials characterized by a very developed interface. Confinement has at least two impacts on a given material, both of which are very strong for liquid crystals: the interaction of the material with the pore surface and the finite size effect. Two important issues must be addressed in the study of confinement effects on LC properties: (1) boundary conditions (i.e. planar-axial or homeotropic-radial orientation of LC molecules on the surface of the solid pore walls of the matrices) and (2) the layer thickness (size of the confinement) of the LC inside cylindrical pores. The thickness of the LC layers formed on pore walls depends on the degree to which pores are filled with LC. We used cylindrical porous matrices in order to control both the boundary conditions (orientation) of LC at interface and the thickness of the confined LC layer. In this paper we report the results of research using dynamic light scattering to examine the influence of confinement and interfaces on the behavior of liquid crystals fille
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