POLYMER INTERDIFFUSION NEAR AN ATTRACTIVE SURFACE. Eric K. Lin and Wen-li Wu, National Institute of Standards and Technology, Gaithersburg, MD, USA. (Building 224, room B320, (301) 975-6743, email:eric.lin@nist.gov)

Applications in areas such as composite materials, electronics packaging, and adhesives require fundamental information about polymer chain dynamics near interfaces and surfaces where the dynamics may significantly differ from the bulk behavior. We seek to determine the characteristic length scale at which an interface continues to perturb the polymer dynamics. Experimentally, the interdiffusion rate between deuterated and hydrogenated poly(methyl methacrylate) (PMMA) layers on silicon substrates is measured using neutron reflectometry. Lower layer thicknesses are prepared ranging from 0.4 to 3.6 radii of gyration (R_g) of the polymer chain (50 - 336A ). The concentration profiles of the deuterated component were measured at different times after annealing above the polymer glass transition temperature with ngstrom resolution for interfacial widths of less than 150A. The rate of interdiffusion decreases significantly as the lower layer size decreases. The thinnest layers have effective diffusion constants almost 2 orders of magnitude smaller than that of the 3.6R_g layer. The results suggest that the attractive interaction energy between the polymer and the substrate affects the chain dynamics at least 2Rg from the substrate surface. The experimental results are interpreted with reference to theoretical self-consistent mean field calculations of the initial polymer chain conformations. The decrease in the polymer dynamics can be attributed to the distorted chain conformations in the initial layer size as well as to the structure of polymer chains adsorbed to the substrate.