Suppression of coalescence by shear and temperature gradients

We describe laboratory experiments on millimeter-sized drops of liquid in air which indicate that both thermocapillary and isothermal shear flows are able to prevent the coalescence of bodies of liquid which would occur readily in the absence of such flows. We have also carried out molecular dynamics computer simulations of nanometer-sized drops, which show the same qualitative behavior in the case of an applied shear. At the other extreme, persistent non-coalescence of larger drops was observed in microgravity conditions in a space shuttle experiment. We give an explanation of the experimental observations based upon lubrication theory and simple continuum hydrodynamics arguments, along with complementary microscopic insight obtained from the molecular simulations. (C) 1996 American Institute of Physics.