Energy dissipation of graphene colloidal suspension droplets impacting on solid substrates

Abstract

The impact and spreading behavior of Newtonian-fluid droplets containing 0.1 mg ml⁻¹ of graphene nanoplatelets (GNP) are quantitatively studied using a high-speed imaging system. Impact regimes for different-sized (micrometer and millimeter) droplets are examined experimentally, and the effects of impact velocity and surface wettability on the impact regime are investigated. In addition, the maximum spreading factor of colloidal suspension droplets is compared with that of droplets without particle immanence and the additional energy dissipation by particle motion in a micrometer-scale droplet is observed. The motion of particles suppresses the spreading of the droplet, such that the maximum spreading factor is reduced by approximately 2% to 5%. Meanwhile, no significant effect of particle motion was observed for millimeter-scale droplets because of different impact regimes. The maximum spreading factor estimated for the GNP suspension droplets is well-matched with a theoretical prediction model of Newtonian-fluid droplets.