ELECTRIFICATION PHENOMENA OF PURE WATER DROPLETS DRIPPING AND SLIDINGON A POLYMER SURFACE

The streaming electrification of pure water is generally thought to be a less problem because of its high conductivity which is six orders o f magnitude higher than that of a hydrocarbon liquid. However, due to the advancement of semiconductor industries, ultrapure water has been used for washing and rinsing processes and it turned out that high deg ree of electrification might be produced by using such ultrapure water . In order to clarify this phenomenon, the electrification of deionize d water droplets dripping to and sliding on a polymer (PTFE) surface h as been investigated. The surface potential distribution of the polyme r plate after electrification is measured by moving a probe for two-di mensional scanning. The charge amount of the droplets after the slidin g is measured by a Faraday cage. From these experiments, several inter esting results were obtained. The potential distribution on the surfac e is not uniform, but varies along the streaming path. At the dripping point the surface potential of the polymer plate always becomes negat ive, then turns to positive downstream. However, the droplet, after sl iding on the polymer surface, becomes electrified positively. This ele ctrification phenomenon depends on the velocity and the conductivity o f droplets. In order to explain this electrification process, a model based on the electric double layer is proposed.