INTERACTION EFFECTS ON THE SIZE OF A POLYMER-CHAIN IN TERNARY SOLUTIONS - A RENORMALIZATION-GROUP STUDY

We calculate the radius of gyration of a polymer coil in a solution containing two different polymer species. The crossover scaling function is determined by renormalized perturbation theory to the order of one loop. Ternary effects manifest themselves most strongly in the crossover and lead to a breakdown of simple power law type analysis. We thus evaluate our result not only in limiting fixed point regions but also present typical examples of crossover behavior. Outside the asymptotic good solvent region ternary effects are large and very sensitive to the value of the intraspecies coupling. This may have consequences for the interpretation of neutron scattering data from mixtures of protonated and deuterated chains.