Collisions of Picoliter Droplets With a Surface

LAUREN MCCARTHY, Jim Walker, Jonathan P. Reid, University of Bristol

     Abstract Number: 67
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
Droplets colliding with surfaces undergo dynamic processes including wetting and oscillating. The precise evolution of these processes is dependent on the properties of the droplet such as its size, surface tension and viscosity, as well as the properties of the surface itself. Studies of droplets colliding with surfaces have largely focused on microliter sizes, using a laser or imaging the system. As the droplet size decreases, high frame rate imaging is required to capture images of droplet oscillations with sufficient time resolution. We have developed a system for observing the dynamics of picoliter droplets, capturing 100,000 frames per second (10 µs). Observed oscillations and contact angle were used to calculate droplet surface tension. Our results indicate that, due to the interference of wetting of droplets this size, accurate determination of surface tension using this method is dependent upon a high contact angle. A high contact angle was achieved using a hydrophobic Teflon surface and high surface tension droplets (> 50 mN m^-1). The wetting of low surface tension water-ethanol droplets (< 25 mN m^-1) on a hydrophilic borosilicate surface is well modelled by Tanner’s law for droplets of this size.