Long-range Casimir interactions between impurities in nematic liquid crystals and the collapse of polymer chains in such solvents

TL;DR

This paper reveals that fluctuation-induced Casimir interactions in nematic liquid crystals can dominate over van der Waals forces near the transition point and can cause polymer chains to collapse abruptly.

Contribution

It introduces the concept that Casimir interactions from nematic director fluctuations can induce polymer collapse, a novel mechanism in liquid crystal-polymer systems.

Findings

Casimir interaction decays as d^(-6) with distance

Interaction dominates near the isotropic-nematic transition

Polymer chains can collapse abruptly due to this interaction

Abstract

The elastic interactions between objects embedded in a nematic liquid crystal are usually caused by the average distorsion-rather than by the fluctuations-of the nematic orientational field. We argue that for sufficiently small particles, the nematic-mediated interaction originates purely from the fluctuations of the nematic director. This Casimir interaction decays as d^(-6), d being the distance between the particles, and it dominates van der Waals interactions close to the isotropic-to-nematic transition. Considering the nematic as a polymer solvent, we show that the onset of this Casimir interaction at the isotropic-to-nematic transition can discontinuously induce the collapse of a flexible polymer chain from the swollen state to the globular state, without crossing the Theta-point.