Thermal- and Rate-Regulated Fast Switchable Adhesion within Glass Transition Zone of an Epoxy Polymer

Thermoresponsive shape memory polymer (SMP) adhesives have demonstrated a high adhesion strength and large switching ratios on different substrates. However, a long response time to switch adhesion on or off is generally encountered. This study provides a fast adhesion switching method based on the temperature and rate dependence of adhesion within the glass-transition zone of an epoxy polymer. The epoxy polymer samples were prepared. The molecular structure and thermal and mechanical properties of samples were characterized. The adhesion of the epoxy polymer sample against a hemispherical glass indenter was measured. Effects of preset temperature and retraction speed on adhesion were investigated, and the switchable adhesion properties were evaluated. The results show that there exists a critical retraction speed (V_c) that makes the viscoelasticity and adhesion maximum at each preset temperature. The viscoelasticity and adhesion gradually enhance below V_c and gradually weaken above V_c with the increasing retraction speed, indicating that the effects of the temperature and retraction speed on adhesion originate from the viscoelastic difference of the epoxy polymer sample under different temperature and rate conditions. The pull-off force (F_pull-off) is verified to linearly depend on the dissipated energy ratio (r), work done during pulling off (U₃), reduced modulus (E_r), and contact radius a_pull-off, i.e., F_pull-off ∝ $$. The epoxy polymer-based switchable adhesion demonstrates high adhesion strength (∼488 kPa), large switching ratio (approaching infinity), and short switching time (<100 ms) simultaneously based on the dual regulation strategy of temperature and rate. This study provides insights into fast adhesion switching and may activate the development and applications of relevant techniques and devices.