When drops move on surfaces, a stress singularity arises at the contact line, due to which a classical analysis tells us that drops cannot move. To overcome this fallacy, various theories of what happens at the contact line have been proposed, most of which have been verified only at low velocities. Surprisingly, hardly anything was known about fast motion of drops on surfaces, which most of us would have seen on lotus leaves, in addition to its importance in designing self-cleaning surfaces and fast throughput microfluidics. We studied such fast motion of drops on surfaces for the first time and proposed theoretical expressions for the velocity of drops, based on the proposition that layers form inside the drops near the solid surface where the viscous effects are restrained. Inertia was shown to be important for the drop velocity, but not for the variation of the contact angle; a result which disproved many theories of contact line motion.

Submitted by Dr. A. P. Baburaj

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