Resonance phenomena of a single water droplet located on a hydrophobic sheet under AC electric field

Resonance vibration of a water droplet located on the surface of a hydrophobic sheet under an AC electric field was investigated experimentally. In order to confirm the effect of the surface property of hydrophobic material on the resonance phenomena of a water droplet, three kinds of hydrophobic materials-silicone rubber (SR), polytetrafluoroethylene (PTFE) and polydimethylsiloxane-grafted fluoropolymer (PGF) sheet-were used. A single water droplet with a volume from 3 to 30 /spl mu/l was placed between parallel electrodes which formed a uniform electric field in the tangential direction along the surface of the hydrophobic sheet. A water droplet under an AC field vibrates strongly only at a particular frequency range. The resonance frequency where the water droplet vibrates strongly decreases with increasing the volume of the water droplet. The resonance frequency on the SR sheet is lower than that on the PTFE and the PGF sheet. The resonance frequency and the magnitude of the deformation of the water droplet depend on the surface properties of the hydrophobic material.