Filtration of deformable emulsion droplets

Oil-in-water (o/w) emulsions of different droplet size were filtered on membranes of various pore sizes to investigate the growth and behaviour of o/w filter cakes. The cake desorptivity S and the filter membrane resistance R were measured at various filtration pressures P. The variation of S with P shows that filter cake oil droplets of radius a are effectively rigid for P ≪ γ / a and fully deformable for P ≫ γ / a , where γ is the oil–water interfacial tension. For the largest P, when S became P-independent, the filter cake remained water-permeable as expected from theory. Although relatively rigid when the driving pressures are small, emulsion droplets are found to increasingly deform under larger applied pressures. Interestingly, the gaps between the droplets never completely close even at the highest pressures.