Strong, Reversible, Heat‐Activated Adhesion from Liquid Crystal Polymer Networks

Abstract

Abstract Smart adhesives that undergo reversible detachment in response to external stimuli can be utilized for clean debonding on demand or for multi‐use purposes. Herein, robust and multi‐use adhesives are developed based on liquid crystal polymer networks. By controlling the glass transition temperatures (Tg), dry liquid crystal adhesives are fabricated with Tg ranging from 14 to 28 °C. These adhesives exhibit low tackiness at room temperature; however, upon heating and annealing, they can be activated, enabling effective deployment. The adhesion tack force increased after annealing from 1 to 7 N for liquid crystal network formulation with a high Tg (28 °C). At the same time, there is no noticeable change for formulations with Tg lower than room temperature. All formulations exhibit high adhesion strength (peel force) in the nematic region (1.0 to 1.6 Nmm−1) and low peel force in the isotropic region. Furthermore, the adhesives demonstrate the capability for reuse in more than five heating and cooling peeling cycles and have shown remarkable contamination tolerance to sand, oil, and dirt. Moreover, these adhesives display lap shear strengths comparable to those of traditional PSAs, reaching up to 3 MPa, with clean detachment except for the formulation with low Tg, which exhibited cohesive failure.

Keywords

• liquid crystal elastomers
• pressure sensitive adhesive
• responsive polymers
• reversible bonding
• smart adhesion