Thermodynamic suppression of Brownian motion

We have used helium-3 nuclear reaction analysis to measure the Brownian motion (intradiffusion coefficient) of polystyrene in a partially miscible blend with poly(alpha-methylstyrene). In the one-phase region, when the correlation length is close to the polystyrene chain size, the intradiffusion coefficient falls to half of its thermal value. For larger and smaller values of the correlation length, diffusion is normal. These results show that the correlation length of a polymer blend constrains polymer diffusion, as suggested from previous neutron scattering measurements, and mean-field theory.