Structure and dynamics in polymer/layered silicate nanocomposites

A poly(methyl phenyl siloxane) homopolymer is intercalated within the organophilized galleries of layered silicates forming nanocomposites in which the polymer chains are confined within the ∼1.5 nm interlayer spacing. These are found to be equilibrium structures since they are independent of the preparation method whereas the spacing is independent of the hybrid composition as well. Quasielastic neutron scattering investigated the effect of such severe confinement on polymer dynamics. Two relaxation processes corresponding to the methyl group rotation and the polymer segmental relaxation were clearly identified for both the bulk homopolymer and the nanocomposite. The very local process of methyl group rotation was unaffected by the confinement within the silicate galleries. At temperatures above the polymer glass transition temperature, the quasielastic data reveal a strong coupling between the segmental motion and the motion of the surfactant chains of the organosilicate. However, the mean square displacement data show that the segmental process in confinement is actually faster than that of the bulk polymer even when the contribution of the surfactant chains is taken into account.