Binary contacts in semidilute solution: Good and Theta solvents

In this paper we show that the concentration dependence of the plateau shea r elastic modulus and of the viscosity can be understood if two lengths, th e correlation length of concentration fluctuations and the tube diameter, a re considered. To interpret the temperature variation of the viscosity and of the self-diffusion coefficient with the solvent quality, one has to take into account the local viscosity to which monomers are sensitive. This con centration dependent local viscosity, deduced from neutron spin-echo measur ements, is independent of the polymer molecular weights, solvent viscositie s and Theta temperatures. The local viscosity decreases to reach the solven t viscosity value at high temperature, that is, under good solvent conditio ns. The role of the macroscopic concentration on a local scale, seems to in dicate that, in semidilute Theta solutions, the polymers are transparent to each other, as far as dynamic properties are concerned.