ELECTRIFICATION OF POLYMER SURFACE CAUSED BY SLIDING ULTRAPURE WATER

It has been thought that the conductivity of pure water is high enough to neglect the streaming electrification. However, with the recent ad vancement of semiconductor industries, ultrapure water appeared to cau se electrification problems at the washing and the rinsing processes o f semiconductor wafers. The investigation on the electrification pheno menon of polymer (PTFE) surface with ultrapure water is described in t his article. Water droplets are always charged positively after slidin g on the PTFE surface, and the surface potential on PTFE is mostly neg ative and varies along the droplet path becoming positive downstream. As the conductivity of water becomes closer to that of ideal water, th e amount of droplet charge increases drastically. This electrification phenomenon is also enhanced by decreasing the thickness of the PTFE p late. It suggests that the Coulombic force between the charge on the P TFE surface and the mirror image charge is an important factor. We hav e proposed a model which is based on the electric double layer similar to conventional streaming electrification for insulating liquid, assu ming that the charged droplet leaves the excess positive charge on the polymer surface.