Surface phase transitions of polymer solutions: A mean-field study

Polymer solutions adjacent to solid substrates play a fundamental role in a wide range of polymeric systems, such as colloidal suspensions and biomolecular condensates, yet the understanding of the surface phase behaviors of polymer solutions, particularly in poor solvents, remains far from complete. In this work, by using a grand-canonical self-consistent field theory, we systematically examine the surface phase behaviors of a homopolymer solution in poor solvents near a single impenetrable surface. For saturated dilute polymer solutions, decreasing solvent quality can result in a depletion-adsorption transition at weakly attractive surfaces, a second-order wetting transition at moderately attractive surfaces, and a first-order wetting transition at strongly attractive surfaces. In contrast, for concentrated polymer solutions at coexistence, decreasing solvent quality may induce a first-order drying transition, a second-order drying transition, and an adsorption-depletion transition, for surfaces with increasing attractive strength toward polymers. We also examine the accompanying prewetting and predrying transitions for solutions off the coexistence curve as well as the effect of chain length. Our work provides the first unified and comprehensive picture of the surface phase behaviors of polymer solutions in poor solvents.