DROPLET INTERACTION IN THE SPINODAL DECOMPOSITION OF A FLUID

The interaction between a pair of non-Brownian droplets in the spinoda l decomposition of a binary fluid is examined. The interaction arises due to the convective term in the model H momentum equation, which is reciprocal to the convective term in the concentration equation. The d ominant contribution to this convective term is due to the interface b etween the droplet and the matrix, where concentration gradients are l arge, and this contribution is determined in the limit where the dista nce between the droplets L is large compared to the radius of a drople t R. The force on the fluid due to the interfacial concentration gradi ent is first calculated, and it is found that there is a net force on the fluid only if there is a deviation of the interfacial concentratio n profile from the equilibrium profile. This deviation is related to t he flux of solute at the interface, which is calculated correctly to ( R/L)(2) for the interacting droplets. The average velocity of the drop lets is then calculated by solving the momentum equations for the syst em. It is found that the interaction between the droplets does cause a spontaneous motion of the droplets towards each other. (C) 1998 Ameri can Institute of Physics. [S0021-9606(98)50741-6].