Fast Drop Movements Resulting from the Phase Change on a Gradient Surface
Susan Daniel,
Manoj K. Chaudhury,*
John
C. Chen
The movement of liquid drops on a surface with a radial
surface tension gradient is described here. When saturated steam passes over a colder hydrophobic substrate, numerous water droplets nucleate and grow by coalescence with the surrounding drops. The merging droplets exhibit two-dimensional random motion somewhat like the Brownian movements of colloidal particles. When a surface tension gradient is designed into the substrate surface, the random movements of droplets are biased toward the more wettable side of the surface. Powered by the energies of coalescence and collimated by the forces of
the chemical gradient, small drops (0.1 to 0.3 millimeter) display
speeds that are hundreds to thousands of times faster than those of
typical Marangoni flows. This effect has implications for passively
enhancing heat transfer in heat exchangers and heat pipes.
Department of Chemical Engineering, Lehigh University, Bethlehem,
PA 18015, USA.
*
To whom correspondence should be addressed.
