Diffusiophoresis of concentrated suspensions of liquid drops

The diffusiophoresis of concentrated suspensions of liquid drops subject to a small electrolyte gradient is analyzed theoretically at arbitrary levels of surface potential and double-layer thickness. The effect of double-layer polarization and double-layer overlapping is taken into account. Kuwabara's unit cell model is employed in modeling the suspension system, and a pseudospectral method based on Chebyshev polynomial is adopted to solve the resulting general electrokinetic equations. Key factors are examined such as the thickness of the electric double layer, the magnitude of the surface potential, the volume fraction of liquid drops, and the viscosity of the internal fluid. The results presented here add another dimension to the previous corresponding study of rigid particles by considering the internal flow of liquid drops, characterized by their viscosity. It is found, among other things, that the lower the viscosity of the internal fluid, the greater the diffusiophoretic velocity of liquid drops. In particular, the diffusiophoretic velocity of an invicid drop is about 3 times higher than that of a rigid one, whereas it is about 2 times higher for a liquid drop with a viscosity similar to that of the suspending medium. The surfactant that might be absorbed on the droplet surface is crucial to the overall observations made above, though.