星野 勝義

It is empirically known that titanium dioxide nanoparticles stabilize the contact and frictional charge of the host polymers to which they are added. However, the mechanism for the stabilization process has not yet been elucidated. In this study, polyester films doped with titanium dioxide nanoparticles of different crystalline forms were triboelectrically charged and the effect of humidity on their charging characteristics was subsequently investigated to elucidate the charge stabilization mechanism. Our first finding was that the rutile-, rutile–anatase mixed crystal (P25)-, and amorphous-dominant-type titanium dioxide nanoparticles reduced the sensitivity of the films to humidity (humidity dependence), while the anatase-type titanium dioxide enhanced the humidity dependence. This difference in action was explained by associating it with the different water adsorption forms on the major crystalline surface of each titanium dioxide type. The second finding was that doping with titanium dioxide nanoparticles, particularly rutile and P25 nanoparticles, reduced fluctuations in the amount of tribocharges of the polyester film. This crystalline-form-dependent difference in action was considered to be based on the depth of the electron traps involved in each titanium dioxide type. The above two findings have allowed us to propose the first mechanism of tribocharge stabilization by titanium dioxide.