DYNAMIC PROPERTIES OF SEMIDILUTE SOLUTIONS AT THE THETA-POINT

Here we report results obtained by neutron spin echo on semidilute the ta solutions of polystyrene in deuterated cyclohexane. It is shown tha t the pertinent length for the diffusion coefficient is not the correl ation length xi(theta) of concentration fluctuations but rather the di stance between binary contacts. At length scales smaller than this dis tance, the dynamics is linked to the local viscosity, which is found t o be surprisingly concentration and temperature dependent.