Enhanced photocontrollable dynamic adhesion of nematic elastomers on rough surfaces

Polymers with switchable adhesion properties are important for efficient catch-and-release processes in robotic hand applications and handgrips with on-demand adhesion control. However, counter objects often have a rough surface topography, which requires a dynamic adhesion system that balances adhesion and detachment performances. Here, we demonstrate that a photosensitive nematic main-chain liquid crystal elastomer (LCE) has suitable photoswitchable adhesion properties on surfaces with micrometer-scale roughness, resulting in a large adhesion change. The nematic LCE exhibits the so-called “soft elasticity,” wherein it can deform at a certain strain without increasing the elastic energy. Such deformation can be maintained owing to arrested relaxation, enabling the LCE to deform along with a rough surface upon light pressure. This increases the contact area and consequently enhances adhesion ability. On the other hand, the LCE exhibits rubber elasticity after proper light irradiation owing to a phase transition from the nematic to the isotropic phase. As rubber elasticity limits deformation, the contact area on the rough surface, and thus the adhesion, is greatly reduced. This LCE with photoswitchable elasticity has great merit as a dynamic adhesive pad for treating objects with rough surfaces, which may expand the versatility of stimuli-responsive adhesive systems.