POLYMER INTERDIFFUSION NEAR AN ATTRACTIVE SOLID SUBSTRATE

Neutron reflectometry is used to study interdiffusion in bilayers of h ydrogenated and deuterated poly(methyl methacrylate) (PMMA) an silicon substrates where the polymer-substrate interaction energy is strongly attractive. The effect of the polymer-substrate interaction energy on the interdiffusion rate as a function of distance from the surface is investigated. Samples are prepared with lower layer thicknesses of th e deuterated PMMA ranging from 35 to 335 Angstrom or 0.4 to 3.6 radii of gyration (R-g) of the bulk polymer chain. The rate of interdiffusio n is found to he strongly dependent upon the lower film size. Polymers in films less than R-g in thickness have effective diffusion constant s 2 orders of magnitude smaller than polymers in the thickest films. T he effective range of the substrate on the interdiffusion dynamics is found to be between 300 and 400 Angstrom or 3 R-g and 4 R-g. The obser ved dynamics are attributed to the different polymer chain conformatio ns at varying distances from the solid surface.