Density of Obstacles Affects Diffusion in Adsorbed Polymer Layers.

The translational diffusion of molecules dispersed into polymer matrices slows down tremendously when approaching a nonrepulsive interface. To unravel the origin of this phenomenon, we investigated the diffusion of molecular probes in the direction normal to an adsorbing wall. Using adsorbed polymer layers as matrices, we were able to decouple interfacial and finite size effects and determined the relation between the diffusion time and the area available at the polymer/solid interface. Based on the results of our investigation, we present a physical picture, suggesting that the reduction in diffusion rate is correlated to the degree of chain adsorption onto the substrate, that is, the density of surface obstacles encountered by tracer molecules.