Phase transitions of nematic rubbers

TL;DR

This paper investigates the phase transition behaviors of nematic rubbers, revealing intrinsic anisotropy in samples, the nature of spinodal limits, and martensitic-like nucleation during the N to I transition.

Contribution

It provides new insights into the anisotropic properties and transition mechanisms of nematic rubbers, including the absence of a soft mode at the spinodal and the martensitic-like nucleation process.

Findings

Samples are intrinsically anisotropic with temperature-dependent birefringence.

No soft mode at the standard spinodal temperature during N->I transition.

Nucleation occurs as platelets at specific angles, resembling martensitic transformations.

Abstract

Single crystal nematic elastomers undergo a transition from a strongly ordered phase N to an "isotropic" phase I. We show that: (a) samples produced under tension by the Finkelmann procedure are intrinsically anisotropic and should show a small (temperature dependent) birefringence in the high temperature I phase. (b) for the I->Ntransition via cooling there is a spinodal limit but for the N->I transition via heating there is no soft mode at the standard spinodal temperature. (c) the N->I transition is reminiscent of a martensitic transformation: nucleation of the I phase should occur in the form of platelets, making a well defined angle with the director.