Aggregation Inhibition of Nanoparticle Dispersion by Nonthermal Plasma Irradiation

The nonthermal plasma has a high chemical reactivity and a characteristic that the temperature of the ion and the neutral particle are relatively low as from room temperature to several hundreds of degrees. Utilizing these features, we are developing applications in the environmental field such as ozone generation, exhaust gas treatment, air cleaning, etc. In recent years, researches directed toward application to medical fields such as sterilization, dental treatment, wound care are actively conducted. Nanoparticles have received much attention in recent years due to its remarkable properties, which offer important economic benefits and have been used in diverse application. However, their property gradually decays because of aggregation, which means that adhesion between nanoparticles. To maintain high performance of nanoparticles in liquid requires a technique which maintains dispersion. Examples of conventional dispersion techniques include a bead mill, an ultrasonic homogenizer, a dispersant, and so on. Due to the disadvantages of conventional dispersion technologies, research on new dispersion technology has been conducted to solve these problems. In this study, we show the experimental result that aggregation of metal oxide nanoparticle dispersion which charged positively was suppressed by irradiating nonthermal plasma. We used nanoparticles of ZrO2 and ZnO, ZrO2 is positively charged in aqueous solution, whereas ZnO is negatively charged in aqueous solution. We compared with dispersion lifetime of two metal oxide nanoparticle dispersions that were irradiated with plasma. The result was ZrO2 dispersion could extend the lifetime, but not ZnO dispersion. These results suggest that OH radical affects the surface hydroxyl group to change the charged state.