BROAD-BAND DIELECTRIC-SPECTROSCOPY ON THE MOLECULAR-DYNAMICS OF BULK AND ADSORBED POLY(DIMETHYLSILOXANE)

Broad-band dielectric spectroscopy (10(-1)-10(6) Hz) was employed to compare the molecular dynamics of poly(dimethylsiloxane) (PDMS) and its mixtures with hydrophilic and hydrophobic Aerosil (fumed silica). After quenching from ambient temperature and subsequent reheating to about 150 K, pure PDMS exhibits the alpha-relaxation in the amorphous state. At higher temperatures the alpha(c)-relaxation process, which is assigned to the relaxation of the amorphous fraction in the semicrystalline polymer, is observed. Filled PDMS shows in contrast three distinct relaxation processes which originate from the varying degree of interaction with the filler surface. These processes are assigned to the relaxation of directly bound, interfacial, and nonadsorbed PDMS in the mixture. Restrictions of chain motions in the adsorption layer are smaller for the mixture with hydrophobic Aerosil in comparison with the hydrophilic one. The results are compared with previous NMR data for the same systems.