Molecular dynamics in grafted layers of poly(dimethylsiloxane)

Dielectric relaxation spectroscopy (10(-1) Hz to 10(6) Hz) is employed to study the molecular dynamics of poly(dimethylsiloxane) (PDMS, M-w = 1.7x10(5) g mol(-1) and M-w = 9.6x10(4) g mol(-1)) as grafted films with thicknesses d below and above the radius of gyration R-g. For the thinnest films the molecular dynamics becomes faster by up to two orders of magnitude with respect to the bulk resulting in a pronounced decrease of the Vogel temperature T-0 and hence the calorimetric glass transition temperature T-g. For films with d = 41 nm>R-g the molecular dynamics is comparable to that of the bulk melt. The results are interpreted in terms of a chain confinement effect and compared with findings for low molecular weight glass forming liquids contained in nanoporous materials. Crystallization effects-well known for PDMS-are observed for films of thicknesses above and below R-g. (C) 2003 American Institute of Physics.