Polymer interdiffusion near the polymer/solid interface is studied using neutron reflectometry. Bilayers of hydrogenated polystyrene (hPS) and deuterated polystyrene (dPS) or hydrogenated dicarboxy terminated polystyrene (hPS(COOH)2) and dPS are prepared on silicon substrates. The thickness of the bottom layer is varied from less than the bulk radius of gyration, Rg, to 4 Rg for hPS and up to 10 Rg for hPS(COOH)2). The effective diffusion coefficient, Deff, characterizing the rate of interdiffusion between the two layers, deviate from the bulk rate when the thickness of the hPS bottom layer is less than 2 Rg. Deff measured in hPS(COOH)2/dPS samples are all lower than those in hPS/dPS bilayers with similar thickness and reach an asymptotic value when the bottom layer is 2 Rg thick. The reduced mobility is attributed to the favorable interaction between the carboxyl end group of hPS(COOH)2 and the silicon oxide substrate surface, as well as hydrogen bonding between polymer chain ends themselves.
Citation: Polymer Engineering and Science
Pub Type: Journals
end-functional polystyrene, interdiffusion, neutron reflectrometry surface, thin film