CHEMICAPILLARY MOTION OF A DROP IN A SOLUTION WITH SIMULTANEOUS DIFFUSION AND CHEMICAL-REACTION AT THE INTERFACE

The slow, steady motion of a drop in a stagnant surfactant solution im miscible with the drop is discussed. The surfactant is assumed to be s oluble only in the liquid outside the drop. Mass transfer toward the d rop surface is driven by convective diffusion in the solution. Adsorpt ion of the surfactant at the interface, surface diffusion, and sorptio n (desorption) of the surfactant due to a first-order superficial chem ical reaction are considered. The motion due to the Marangoni effect, the change in surface tension caused by the presence of a surfactant a t the interface, is studied. The effects of determining parameters suc h as the physical properties of the phases, the volume and surface dif fusivities of the surfactant, and the rate constant of the chemical re action on the force exerted on the drop are analyzed. The parametric r egions in which this force is either a drag force or has the same dire ction as the velocity vector of the drop are constructed.