Spontaneous Charge-Driven Surface Oscillations of Adhesive Silicone Gels

Soft adhesion is ubiquitous in everyday systems, yet the dynamic process by which soft solids initiate and grow contact with rigid solids remains poorly understood. We investigate the dynamics of adhesive contact between a soft polydimethylsiloxane (PDMS) gel and a rigid glass microsphere using brightfield, high-speed imaging. We focus on early-time contact evolution from initial approach to full contact. Unexpectedly, we observe spontaneous, charge-driven surface oscillations of the PDMS when brought ~10 micrometers away from an electrostatically charged glass tip. This surprising phenomenon can last for hundreds of seconds or more, depending on initial conditions, specific gel composition, and humidity. We contrast this with observations of electrically-neutral contact initiation.