Effect of layer age and interfacial relaxations on the self-exchange kinetics of poly(ethylene oxide) adsorbed on silica

The interfacial states in adsorbed PEO layers on silica were probed through the self-exchange of coumarin-tagged chains and native analogues. New evid ence for nonequilibrium interfacial behavior is presented, though prior stu dies supported local equilibrium for adsorbed PEG. Results suggest that ent anglements or high numbers of segment-surface contacts can be as important as a high bulk T-g in leading to trapped interfacial chains, interfacial "g lasses" can occur for systems where bulk (solution or melt) states are not glassy. For the specific PEO-water-silica. system, measurable relaxations p ersisted for the first 10 h of layer incubation in pure solvent. Additional relaxations may have occurred beyond this time; however, such additional i nterfacial evolution was not detectable by self-exchange. Self-exchange was generally incomplete, often revealing a population of chains whose attachm ent to the surface appeared irreversible and suggesting that various interf acial states, differing in their extent of surface attachment, are long-liv ed.