Drag coefficient of a spherical droplet immersed in a near-critical binary fluid mixture

We consider a spherical liquid droplet immersed in a near-critical binary fluid mixture. Aweak preferential attraction is assumed between the droplet and one of the two mixture components, and the difference in the viscosity is neglected between the mixture components. Using the Gaussian free-energy functional, we calculate the drag coefficient of a droplet. Whether it is increased or decreased by the preferential attraction turns out to depend on the bulk correlation length and the ratio of the viscosity of the surrounding mixture to that of the droplet.