Adsorbed Polymer Multilayers in a Bad Solvent

There are general thermodynamic arguments to expect, for any mixture in contact with a surface, that above the 'wetting temperature' the surface can stabilize a microscopic phase that would still be unstable in the bulk. The physical reason is that an intervening multilayer region can lower the free energy of the interface between the adsorbed layer and the free solution. These conclusions are based on various approximations and assumptions. No account is taken of a chain's internal structure. A chain becomes deformed when it is adsorbed, losing internal entropy. Here the authors consider experimentally the conditions for multilayer adsorption of polymers. The results agree with general theories of wetting and imply that multilayers can persist up to temperatures considerably above the coexistence temperature (at least 10°C). They also discuss the possibility that when the molecular weight of the polymer is sufficiently high, multilayer adsorption of chains may present interesting new varieties of behavior not encountered with small molecules.