Stuck on Repeat: Dynamic Liquid Crystal Elastomers as (Re)trainable Adhesives

Polymeric networks whose performance can be trained as a function of mechanical inputs provide additional possibilities, as they offer an opportunity to further modulate a material's properties post-synthesis and processing. Herein, disulfide-containing dynamic liquid crystal elastomer (LCE) adhesives exhibiting (re)trainable multistage adhesive character are reported. Synthetic tailoring of the mesogen lateral substituent size allows for direct tuning of the thermal properties (<i>T</i>_g and <i>T</i>_NI) of the network. These dynamic LCEs exhibit pressure-tunable adhesive behavior as a result of their inherent soft elasticity and stimuli-responsive dynamic bonds. Furthermore, higher-strength hot melt adhesive joints can be formed through the activation of the incorporated dynamic disulfide bonds at high temperatures (>150 °C). General adhesive performance can be tuned through mesogen structure, while multicycle probe-tack tests show that their force of adhesion increases with each cycle, demonstrating the trainability of the pressure-tunable adhesive response with repeated use. Thermal disruption of the LC phase resets the adhesive character, which can be subsequently reattained through mechanical training.