Highly switchable and reversible soft sticky adhesives based on thermo-responsive phase separation

Abstract

Many biological systems can switch between strong adhering and non-adhering states to various materials with complex shapes and sizes in a reversible manner. By contrast, synthetic soft sticky adhesives, or pressure-sensitive adhesives, still face challenges in combining high switchability, reversible switching, facile switching operation, and applicability to diverse materials, shapes, and sizes. To address this challenge, here we present a highly switchable and reversible soft sticky adhesive based on thermal-induced phase separation in a thermo-responsive hydrogel. At room temperature, the hydrogel adhesive is toughened by nanoclay as noncovalent crosslinkers, showing an adhesion strength of 60–80 kPa to various adherends. This adhesion is almost completely switched off upon heating, with a residual strength of around 1 kPa. The switching is reversible for many cycles, enabling selective pick-and-release of objects with various materials, shapes, sizes, and weights. The switching time is around 10 s with an adhesive layer of 1 mm, governed by thermal conduction through the adhesive, faster than or comparable to most state-of-the-art methods. The adhesive is self-healing, and can be recycled, dried, stored, reswollen, and reused with nearly intact adhesion and switching properties. These features are hoped to advance technologies such as on-demand device disassembly for recycling, assembly-based manufacturing, biomimetic robots, and human-machine interfaces.