Buckling transition of nematic gels in confined geometry

TL;DR

This paper reports the observation of a spontaneous buckling transition in thin nematic liquid crystalline gels confined between glass surfaces, driven by the coupling of liquid crystal ordering and polymer network deformation.

Contribution

It introduces an experimental observation of buckling in nematic gels and provides a theoretical explanation based on rubber elasticity and instability analysis.

Findings

Buckling occurs as temperature decreases and nematic order increases.

Stripe patterns form due to spatial modulation of the nematic director.

Critical parameters like wavelength relate to temperature and elastic properties.

Abstract

A spontaneous buckling transition in thin layers of monodomain nematic liquid crystalline gel was observed by polarized light microscopy. The coupling between the orientational ordering of liquid crystalline solvent and the translational ordering of crosslinked polymer backbones inside the nematic gel contributes to such buckling transition. As the nematic mesogens become more ordered when the gel is cooled down from a higher gelation temperature, the polymeric backbones tend to elongate along the direction parallel to the nematic director, which is perpendicular to the rigid glass surfaces in the experimental setup. The shape change of such confined gel sample lead to the spontaneous buckling of polymeric network and the spatial modulation of nematic liquid crystalline director, which is observed as the stripe patterns. The instability analysis was used to explain such transitions, and the relationship between the critical field, stripe's wavelength and temperature can be explained qualitatively by the rubber elasticity theory for liquid crystalline gels.