
Electromechanical excitation of soft contacts for adhesion regulation
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Adhesion in soft viscoelastic contacts is crucial for applications in soft robotics, grippers, smart manipulators, and reversible adhesive pads [1, 2]. Recent studies have revealed that fast, low-amplitude vibrations can drastically alter adhesion in soft elastomers. This study examines the adhesive behavior of a borosilicate spherical lens suspended on a soft spring in contact with a soft PDMS (Polydimethylsiloxane) substrate, excited by two electrodynamic shakers at high frequencies (>100 Hz) and micrometrical amplitudes (~100 µm) [3]. Experimental results demonstrate that tuning the vibration frequency and amplitude enhances the pull-off force—required to separate the contact—by more than 1400% compared to quasi-static conditions (i.e., without vibration). This effect arises from the viscoelastic properties of the elastomer: under high-frequency vibration, viscoelastic energy dissipation within the material increases the interface's effective toughness during crack propagation and decreases it during crack healing. A reduced-order model was developed to interpret these findings, coupling a viscoelastic contact model with the dynamical behavior of the glass sphere (the indenter), which acts as a nonlinear oscillator. The study highlights how the contact constitutive model interacts with the indenter's dynamical response to enable a wide range of adhesion regulation, with adhesion that peaks at resonance. After characterizing the rate-dependent adhesive behavior of the PDMS interface, theoretical predictions were compared with experimental results, showing excellent agreement [3]. However, discrepancies were observed above a vibration amplitude of 100 µm, where additional nonlinear effects likely occur but were not included in the developed model.