Polydomain structure and its origins in isotropic-genesis nematic elastomers

TL;DR

This paper develops a theoretical framework to understand the polydomain structures in isotropic-genesis nematic elastomers, revealing how network heterogeneity stabilizes isotropic states and induces short-range oscillatory nematic order.

Contribution

It introduces a phenomenological replica Hamiltonian and Gaussian variational analysis to explain the effects of disorder and fluctuations in nematic elastomers.

Findings

Polydomain state stabilized by network heterogeneity.

Short-range oscillatory nematic order predicted at low temperatures.

The approach applies to other randomly crosslinked solids.

Abstract

We address the physics of nematic liquid crystalline elastomers randomly crosslinked in the isotropic state. To do this, we construct a phenomenological effective replica Hamiltonian in terms of two order-parameter fields: one for the vulcanization, the other for nematic alignment. Using a Gaussian variational approach, we analyze both thermal and quenched fluctuations of the local nematic order, and find that, even for low temperatures, the macroscopically isotropic polydomain state is stabilized by the network heterogeneity. For sufficiently strong disorder and low enough temperature, our theory predicts unusual, short-range oscillatory structure in (i.e., anti-alignment of) the local nematic order. The present approach, which naturally takes into account the compliant, thermally fluctuating and heterogeneous features of elastomeric networks, can also be applied to other types of randomly crosslinked solids.