Reduced mobility of elastomers near a solid surface as measured by neutron reflectometry

The effects of an interacting, hydrophobic silicon surface on the interfacial properties of the immiscible polymer blend polybutadiene (PB) and brominated poly(isobutylene-co-p-methylstyrene) (BIMS) were studied using neutron reflectivity (NR). The results show that an adsorbed polymer layer, approximately 2R_g (R_g is the radius of gyration) thick, is always present at the silicon interface. This observation confirms the existence of an immobile gel-like layer which was invoked by numerous authors to explain the reduced dynamics and anomalous theological properties of polymers at long distances from interactive substrates. The attractive substrate was also shown to affect the equilibrium interracial width between the immiscible polymers. Narrowing of the interfacial width was observed only when the layer adjacent to the silicon substrate was less than 3R_g thick, indicating that only chains in direct contact with the interface were affected.