Superhydrophilic Coating Induced Temporary Conductivity for Low-Cost Coating and Patterning of Insulating Surfaces

Superhydrophilic surfaces have attracted attention from more and more fields. Here, based on superhydrophilic coatings, insulating substrates are made temporarily conductive and suited for electrostatic powder coating (EPC). Furthermore, by manipulating surface wettability of the substrate, epoxy-polyester powder particles are directly assembled into patterns in air under electrostatic attraction. First, electrically insulating substrates are treated to be superhydrophilic with composite nanoparticles of TiO2 and SiO2. Water droplets sprayed onto the surface could spread completely and connect together to form uniform thin water films (40 m). The liquid films make the insulating surfaces conductive enough for EPC, which is an environmentally friendly coating process widely applied to conductive workpieces, such as metals. The first pass transfer efficiency (FPTE) is promoted to more than 80%, which is equal to or even greater than those of metal workpieces. Second, FPTE is quite different on surfaces with different wettability. Negatively charged epoxy-polyester powder particles are attracted toward positively charged water film formed on superhydrophilic coatings. And few powders deposit on untreated nonconductive areas. Compared with electrostatic self-assembly in solutions, this strategy is suited for rapid assembling various kinds of particles into large area patterns.