Diffusion of Poly(dimethylsiloxane) Mixtures with Silicate Nanoparticles

Pulsed field-gradient (PFG) NMR has been used to measure self-diffusion coefficients in mixtures of silicate nanoparticles with poly(dimethylsiloxane)s as a function of volume fraction of particles and of polymer molecular weight. Two different sizes of nanoparticles were used: the smaller acted like a solvent, and the larger one acted more like a colloidal particle. In the former case, two distinct diffusion coefficients were obtained, corresponding to the particle and the polymer. In the second case, only a signal from the polymer was evident because of the short spin−spin relaxation time ( T 2 ) of the particle. However, in this latter case the diffusional attenuation indicated the presence of both free polymer and locally mobile but translationally constrained polymer, characteristic of polymer adsorption from a liquid. The data have been interpreted as a function of particle loading, and calculations have been made to estimate the thickness of the polymer layer using a hydrodynamic model.