Nematic-Isotropic Transition with Quenched Disorder

TL;DR

This paper investigates how quenched disorder from network crosslinks in nematic elastomers alters their phase transition, transforming it from a first-order to a continuous transition by singularly renormalizing the Landau-De Gennes free energy.

Contribution

It demonstrates that weak random anisotropy causes a singular renormalization of the phase transition, leading to a continuous transition at high disorder levels, contrary to mean field predictions.

Findings

Disorder reduces the first-order jump in the order parameter.

High disorder strength results in a continuous phase transition.

The transition resembles supercritical transitions in external fields.

Abstract

Nematic elastomers do not show the discontinuous, first-order, phase transition that the Landau-De Gennes mean field theory predicts for a quadrupolar ordering in 3D. We attribute this behavior to the presence of network crosslinks, which act as sources of quenched orientational disorder. We show that the addition of weak random anisotropy results in a singular renormalization of the Landau-De Gennes expression, adding an energy term proportional to the inverse quartic power of order parameter Q. This reduces the first-order discontinuity in Q. For sufficiently high disorder strength the jump disappears altogether and the phase transition becomes continuous, in some ways resembling the supercritical transitions in external field.