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Title:The effect of shear flow on the isotropic-nematic transition in liquid crystals
Author(s):Olmsted, Peter David
Doctoral Committee Chair(s):Goldbart, Paul M.
Department / Program:Physics, Condensed Matter
Physics, Fluid and Plasma
Discipline:Physics, Condensed Matter
Physics, Fluid and Plasma
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Physics, Condensed Matter
Physics, Fluid and Plasma
Abstract:In this thesis I will discuss the effects of shear flow on the Isotropic-Nematic phase transition in liquid crystals. Shear flow has dramatic orienting effects on the rod-like constituents of nematic liquid crystals, with the general effects of (1) inducing order in the high-temperature isotropic phase, and (2) dictating a direction of alignment for the low-temperature nematic phase. Shear flow also imposes a biaxial symmetry on both the high and low temperature phases, thereby changing the nature of the symmetry-breaking at the transition.
We develop coupled deterministic dynamical equations for the 5-component nematic order parameter and the fluid velocity, which may be considered generalizations of the Leslie-Ericksen and Navier-Stokes equations, respectively. We examine the stable stationary solutions to these equations to determine the nature of the non-equilibrium phases, and discuss the analogies and differences between this system and equilibrium systems. From homogeneous solutions we obtain a state diagram analogous to that of a Van der Waals fluid, including a two-state region and a discontinuous transition which terminates at a critical point. To resolve the question of the analog of the Maxwell construction to distinguish locally stable states, we construct stable inhomogeneous interfacial states. From an analysis of these states we determine a coexistence line and find exponents characterizing the shape of the coexistence curve and the interface thickness as the critical point is approached. We find mean-field critical behavior, and comment on the possibility of the analogs of spinodal decomposition and nucleation.
Finally, we develop a formalism for describing light scattering from biaxial steady state, and investigate the Gaussian level fluctuations about these states. In the vicinity of the critical point we find singular behavior analogous to critical opalescence of a simple fluid at its critical point. We also find anisotropic correlations at the critical point which reflect the manner in which shear flow suppresses fluctuations, as was found by Onuki and Kawasaki in their studies of a binary fluid under shear flow. We finish by commenting on the application of these ideas to lyotropic systems, and combining flow and magnetic field effects in the same system.
Issue Date:1991
Type:Text
Language:English
URI:http://hdl.handle.net/2142/23675
Rights Information:Copyright 1991 Olmsted, Peter David
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9210941
OCLC Identifier:(UMI)AAI9210941


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