Molecular dynamics of grafted PBLG in the swollen and dried state

We describe a novel experimental approach based on the use of solid electrodes to prepare capacitor arrangements with a thickness in the order of 10 nm containing layers of grafted polymers. It enables study of the molecular dynamics in ultrathin grafted layers of e.g. poly(y-benzyl-L-glutamate) (PBLG) by means of dielectric spectroscopy. The results of our method are compared to those obtained by evaporating the upper electrode on the polymer film and to measurements on the bulk material. In the bulk, two relaxation processes are observed which are assigned to fluctuations of the helical main chain as a whole (chopstick motion) and to fluctuations of the polar side groups. The latter are found to be broadened and to be slowed down in the grafted layer, while the chopstick motion is, depending on the thickness of the grafted layer, two orders of magnitude faster compared with the bulk. This is presumably due to a higher order in the grafted layer. The dielectric dispersion Δε of the side chain motion can be described by assuming free fluctuations of these chains, whereas the model of Wang and Pecora (1980) has been applied for the chopstick motion. After swelling the grafted polymer layer, the side chain fluctuation becomes faster, while the chopstick motion is not influenced