Role of Solvent Washing Conditions on the Creation of Adsorbed Layers from Melt Films

Recent reports have proposed the presence of adsorbed layers may strongly affect dynamics in thin supported films. Often assumptions are made about the presence of adsorbed layers within melt films based on annealing time and temperature, where subsequent washing of films with solvent is interpreted as “revealing” the structure of the adsorbed layer within the melt (so-called Guiselin experiment). However, this interpretation is contrary to extensive literature studies from the 1980-90s on displacement experiments of adsorbed chains in solution measuring exchange kinetics with a third component called the “displacer”, either another polymer or second solvent, that displaces the initially adsorbed polymer due to its preference for the substrate interface. These studies, along with direct surface diffusion measurements by Granick’s group in the regime of strong adsorption, suggest adsorbed polymer chains are extremely mobile during solvent washing. We test this interpretation by demonstrating the measured residual adsorbed layer strongly depends on solvent washing conditions. Consistent with work by Cohen Stuart’s group, we show acetone as a displacer removes nearly all of the initially adsorbed chains, even after melt films were extensively annealed at elevated temperatures.