Evaporation enhancement effect of TiO2 nanoparticles on silicone oil in electrorheological fluid suspension

Abstract

Electrorheological (ER) fluids are suspensions which consist of dielectric particles and insulation fluid. The ER fluids can change from liquid-like to solid-like state under the applied electric field. For traditional ER fluids, the maximum yield/shear stress is only several kPa and the size of dielectric particles is generally of micron. Since 2003, a series of new type ER fluids have been discovered, of which the yield/shear stress is as high as several hundred kPa. Such a type of ER fluid is called giant ER fluid or polar molecule-dominated ER fluid (PM-ER fluid), in which the size of dispersed particles is of nanoscale. Dimethyl silicone oil is the most commonly used dispersing agent in ER fluids, because of its stable physical and chemical behaviors. There is no obvious evaporation in traditional ER fluids when it is mixed with micron grade particles. However, when it is mixed with nanoparticles to prepare giant ER fluids, the silicone oil volatilizes easily in atmosphere. If time is long enough, the silicone oil in ER suspension can even be evaporated completely. In this paper, the existence of TiO2 nanoparticles in ER suspensions enhances the volatilization phenomenon has been studied through experiment. Analysis shows that the nanoparticles caused convex nanoscale curved surfaces on the gas-solid interface makes the vapor pressure increase greatly at the silicone oil surface, and leads to the enhancement of its volatilization. Influence of particle concentration, environmental temperature and viscosity of silicone oil on the evaporation enhancement effect is also studied and analysed systematically. Results show that the increase of the fraction of nanoparticles, viscosity of silicone oil as well as the temperature would promote the effect of evaporation enhancement of silicone oil in the suspensions.