Supramolecular Liquid Crystal Elastomer Adhesives: Role of Internal Damping and Hydrogen Bonding

Abstract

Liquid crystal elastomers (LCEs) have attracted attention as materials for pressure-sensitive adhesives (PSAs) owing to their high internal damping resulting from mesogen reorientation. However, the roles that mesogen reorientation and interfacial interactions play in overall adhesion remain unclear. In this study, a series of supramolecular LCE-based PSAs are prepared by systematically varying the liquid crystal (LC) content and hydrogen bond (H-bond) density to investigate their effects on internal damping, soft elasticity, and adhesion strength. A decreased LC content of the PSAs reduces both internal damping and soft elasticity, resulting in weaker adhesion. When H-bonds are introduced using non-mesogenic monomers in the rigid segment, the mesogen reorientation is restricted, thereby decreasing adhesion. In contrast, incorporating H-bonds into the chain extender (or soft segment) of the supramolecular LCEs improves the adhesion strength with increasing H-bond density, provided the LC content is high. Therefore, the adhesion of supramolecular LCEs is primarily governed by internal damping rather than by H-bond interactions. Moreover, solvent vapor annealing enables reversible adhesion in the supramolecular LCEs by transiently weakening H-bonds and improving surface contact. The non-thermal approach demonstrated in this study yields LCE-based PSAs for heat-sensitive applications such as medical adhesives, skin patches, and semiconductor processing.