Tack energy and switchable adhesion of liquid crystal elastomers

TL;DR

This paper investigates the adhesive properties of liquid crystal elastomers (LCEs), demonstrating their potential as switchable pressure-sensitive adhesives through modeling and analysis of their tack energy in different alignments.

Contribution

It introduces a theoretical framework combining the nematic dumbbell model and PSA block model to analyze LCEs' tack energy and switchable adhesion mechanisms.

Findings

Tack energy is over twice as high in parallel director alignment compared to isotropic.

Perpendicular alignment tack energy can be 50% less than isotropic.

Reversible adhesion is achievable via the isotropic-nematic transition mechanism.

Abstract

The mechanical properties of liquid crystal elastomers (LCEs) make them suitable candidates for pressure-sensitive adhesives (PSAs). Using the nematic dumbbell constitutive model, and the block model of PSAs, we study their tack energy and the debonding process as could be measured experimentally in the probe-tack test. To investigate their performance as switchable PSAs we compare the tack energy for the director aligned parallel, and perpendicular to the substrate normal, and for the isotropic state. We find that the tack energy is larger in the parallel alignment than the isotropic case by over a factor of two. The tack energy for the perpendicular alignment can be 50% less than the isotropic case. We propose a mechanism for reversibly switchable adhesion based on the reversibility of the isotropic to nematic transition. Finally we consider the influence of several material parameters that could be used to tune the stress-strain response.