In many studies, the specimens are pretreated in acidic or alkali solutions, to produce a thin film of oxides or hydroxides, before EPD coating. Noticeably, the pretreatment thin films are non-conductive. However, electrophoresis is a process that depends on the presence of a uniform electric field. The pretreatment thin films, on the specimens, hinder the electric field between cathode and anode in EPD cell and must stop the deposition process. But, based on my experience, EPD coatings are deposited on the pretreatment thin films and even some literatures have even recommended the pretreatment for uniform EPD coating. How come the electrophoresis happens against the non-conductive thin film?
A thin non-conductive film is like a weak dielectric and as high voltages are applied on electrophoretic process, the break of dielectric (a weak one) occurs and deposition goes on easily.
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