The effect of partial wetting on the spreading of non-isothermal liquid droplets

GOMBA, J. M.; HOMSY, G. M.

University of California at Los Angeles, Los Angeles, USA.

Simposio; 2nd Southern California Symposium on Flow Physics; 2008

Caltech, UCLA, UCSB, UCSD, USC

The spreading of liquids on rigid surfaces and inside channels is of interest in a variety of applications such as coating processes and microuidic devices. In coating processes, the surface is usually coated by application of a body force, such as gravity in tilting or centrifugal force in spinning the substrate, or by using external thermal gradients. In microuidic devices, the actuation of very small droplets can be accomplished in many different ways such as pneumatic pumping, centrifugation, thermocapillarity and electrowetting, and they have been successfully used to drive ows in both closed channels and on open surfaces. Here we present preliminary results in the study of the efect of non zero contact angle  (partial wettability) on the thermocapilary droplet actuation for liquids on open surfaces. In particular, we analyze the dierences found in flows with low and high contact angle. The dynamic of the process is analyzed under the long wave lubrication approximation, including the effects of capillarity, Marangoni stress and disjoining/conjoining pressure term to account for intermolecular forces at the contact line resulting in an equilibrium molecular scale thickness. (partial wettability) on the thermocapilary droplet actuation for liquids on open surfaces. In particular, we analyze the dierences found in flows with low and high contact angle. The dynamic of the process is analyzed under the long wave lubrication approximation, including the effects of capillarity, Marangoni stress and disjoining/conjoining pressure term to account for intermolecular forces at the contact line resulting in an equilibrium molecular scale thickness.