EWOD-based chip characterization under AC voltage

This paper addresses one basic issue of EWOD chip as a consumable: how to detect the alteration of hydrophobic layers? We investigate the possibility of using droplet oscillations to finely characterize chip ability to EWOD protocols. Experiments are performed in coplanar electrodes configuration. Dedicated setup and software have been developed for a simple in situ characterization. When a low-frequency AC voltage is used, drop surface oscillations are created from the time-varying component of the normal electrostatic stress at drop surface near the contact line. As an analysis tool, our software is based on droplet contour detection and delivers dynamical contact angle and contact line motion. Careful attention is brought to surface wetting or dewetting of the droplet during long-term AC actuation and surface ageing.