Interplay between wetting and phase separation in binary fluid mixtures: roles of hydrodynamics

Here we consider how phase-separation kinetics and morphology are affected by the preferential wetting of a solid surface by one component of a binary fluid mixture. The behaviour is crucially dependent upon whether the spinodal decomposition is bicontinuous-type or droplet-type, i.e. the composition symmetry. Near a symmetric composition, wetting effects are strongly delocalized by hydrodynamic effects unique to bicontinuous phase separation. We discuss the physical mechanism of the unusually fast lateral growth of wetting domains found by Wiltzius and Cumming, the thickening dynamics of wetting layers, and pattern evolution under the influence of surface fields, focusing on the roles of hydrodynamics. We point out a novel possibility of double phase separation: that the quick hydrodynamic reduction of the interface area may spontaneously destabilize the phase-separated macroscopic domains and induce secondary phase separation. We also consider effects of the preferential wetting of immobile and mobile particles by one component of a fluid mixture on phase separation and the resulting complex pattern evolution. It is demonstrated that hydrodynamics always plays crucial roles in the pattern evolution of a phase-separating fluid mixture interacting with solid surfaces.