THERMOCAPILLARY MIGRATION OF WATER DROPLETS ON SUPERHYDROPHILIC SURFACES

Actuation of water droplets by thermocapillary phenomenon is quite challenging due to typically large contact angles and the associated contact angle hysteresis. The present study demonstrates the migration of water droplets over UV treated TiO2 based superhydrophilic surfaces characterized by near 0 degrees contact angle. This technique has a merit of migrating water droplets with moderate temperature gradients without the need for expensive microfabrication procedures and/or patterned wettability microheaters. The influence of droplet volume on the temporal evolution of the velocity is studied for 2 mu l and 6 mu l droplets. The thermocapillary and spreading effects on water droplet migration dynamics are qualitatively explained. Further, fluid flow and heat transfer phenomena inside the droplet during migration are elucidated from emerging thermal patterns captured using infrared (IR) thermography.