Switchable Pressure-Sensitive Adhesion in Nematic Side-Chain Liquid Crystal Elastomers

Switchable pressure-sensitive adhesives (PSAs) offer promising opportunities for reusability, on-demand debonding, and programmable adhesion. In this work, we report the design and synthesis of a novel thiol-functionalized liquid crystal mesogen, enabling the fabrication of side-chain nematic liquid crystal elastomer (SC-LCE) adhesives via siloxane-based thiol-ene click chemistry. These materials uniquely combine the thermomechanical responsiveness of LCEs with rheological profiles that approach the Dahlquist criterion for ideal PSAs. Specifically, the resulting SC-LCEs exhibit a glass transition temperature of 6 °C and a rubbery plateau modulus of 0.3 MPa, achieved without the use of plasticizers, tackifiers, or other additives. In particular, our SC-LCE adhesives exhibit exceptional viscoelastic energy dissipation, with a peak loss factor (tanδ) of 2.81, and maintain high damping (tanδ > 1) over a wide temperature range (0-45 °C) in the nematic phase. SC-LCE adhesives also exhibit tackiness comparable to that of high-performance commercial adhesives such as VHB tapes while maintaining full thermal switchability. Furthermore, the peel and lap shear forces are more than double those of conventional main-chain LCEs. These findings represent a significant advance toward the development of high-performance, thermally debondable, and fully reusable PSA systems with promising implications for sustainable and reconfigurable adhesive technologies.