Is the chain dynamics in thin polymer films isotropic?

The dynamics of molten polymer chains (polydimethylsiloxane) confined between air and a solid, wettable and non-adsorbing surface. is investigated using NMR. The basic approach used here consists in studying how nuclear interactions are time-averaged by rapid molecular motions. Chain segments in such molten films undergo uniaxial reorientations around the normal to the surfaces. The influence of the film thickness h (50 less than or equal to h less than or equal to 3500 Angstrom) proves this dynamic uniaxiality involves rapid segment diffusion between both surfaces which impose a high degree of planar orientation. Thus the segmental ordering is observed over a thickness range which depends on the degree of chain entanglements.