Shaping high-speed Marangoni flow in liquid films by microscale perturbations in surface temperature

The authors show that a variety of controlled flow patterns, including toroidal cells and surface doublets, can be generated in 80-400 mu m thick liquid films by placing scanning microscopy probes with integrated heaters just above the surface (< 400 mu m separation). The probes project sharp temperature gradients on the liquid surface which drive Marangoni flow. Flow velocities approaching 3000 mu m/s are experimentally demonstrated on length scales of 20-200 mu m with < 20 mW input power. For liquids such as water and oil, in which the surface tension coefficient is approximate to 0.2 mN/m K, flows > 1000 mu m/s can be accomplished with surface temperature perturbations < 1 degrees C. This technique enables microfluidic manipulation on unpatterned substrates. (c) 2007 American Institute of Physics.