Abstract
Neutron reflectivity experiments were performed to study the interdiffusion of two compatible polymers, polystyrene and deuterated polystyrene, across a free-standing ultra-thin (60 Å) interstitial membrane. Annealing above the glass transition temperature and quenching back to room temperature allows for a time-dependent study of the changing concentration profile due to membrane-mediated interdiffusion. For the case of matched polymer molecular masses but different isotopic labeling, faster transport of the deuterated polymer across the interstitial layer is observed leading to displacement of the membrane. Varying the molecular mass and isotopic labeling of the top polymer layer provides information about the size discrimination and isotopic selectivity of the membrane.