Degradation of electrowetting for upward and downward electrolyte droplets containing microparticles

Electrowetting (EW) of an electrolyte droplet containing zinc or silica particles was investigated for durability and degradation of devices. Two types of experimental geometries exist, an upward droplet standing on a substrate and a downward droplet hanging under a substrate. Different gravitational effects of droplets for the two geometries shift the contact angle of the EW dynamics. Added zinc and silica particles significantly accelerated the degradation in the EW switching with increased driving time, which may result from the surface damage due to the collision between the particles and surface. The degradation was significantly influenced by many factors such as the particle dispersity, droplet direction, particle concentration, and viscosity of dispersions. Interestingly, the device with a downward droplet degraded much less than that with the upward droplet. Our findings will be highly useful in designing durable microfluidic and EW devices.