Discrete Droplet Manipulation On Liquid Platforms Using Thermal Gradients

Manipulation of droplet motion on the free surface of an liquid platform using thermal gradient has been studied. Two distinct motion mechanisms were observed. Droplets that remain spherical are propelled from cold to warm region and those which break up into a sessile lens move in the opposite direction. Driving forces acting on the droplet due to interfacial-tension gradients arising from induced thermal gradients were analyzed using theoretical models. By adopting a liquid platform, limitations associated with previously-reported capillary-based mechanisms, which used chemical/thermally-patterned solid substrates, are overcome to make the proposed scheme suitable for droplet-based bio-chemical lab on chips: minimal droplet temperature fluctuation (\u3c5°C); avoiding droplet-pinning and contact-angle hysteresis allow for higher transport speeds (~4 mm/sec) and no evaporative losses or contaminations. © 2009