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| Paper IPM / Physic / 13096 |
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We examine fluctuation-induced interactions in nematic liquid-crystalline films confined between two surfaces, one of which is assumed to be a chemically disordered substrate exhibiting a quenched random distribution of anchoring energies. We employ the replica method to evaluate the free energy of interaction mediated between the two surfaces and investigate how the pseudo-Casimir interaction force, generated by the thermal fluctuations of the director field, is influenced by the presence of disordered surface anchoring energy. It is found that the disorder can modify the nematic fluctuation-induced forces drastically and in two different ways. First, it results in a renormalization of the effective surface anchoring parameter and, hence, changes the sign of the pseudo-Casimir interaction force from attraction (in the absence of disorder) to repulsion. Secondly, the disorder generates an additional long-ranged component in the interaction force which is attractive and decays more weakly than the modified pseudo-Casimir component. This additional force dominates at large separations and can thus serve as a more suitable measure for the experimental investigation of fluctuation-induced forces in liquid-crystalline systems.
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