Chain-segment order and dynamics in a grafted polymer melt: A deuterium NMR study

The dynamics of polymer chains grafted on solid substrates is investigated, using deuterium NMR. The experiments are performed on perdeuterated polydimethylsiloxane melts end grafted on porous or planar silica. The method consists in observing how nuclear interactions are time averaged by the molecular motions. One of the main results of this NMR study is that the chain segments exhibit uniaxial reorientations around the direction normal to the solid-polymer interface. Studies versus layer thickness demonstrate that this motional uniaxiality is due to the squeezing of the chains and characterized by a negative order parameter. The orientational fluctuations of segments are preferentially parallel to the grafting plane throughout the whole layer. This implies that orientational correlations take place between chain segments.