Statics and dynamics of single chains in polymer blends and copolymer melts — results beyond the random phase approximation

We present new results on the behaviour of single chains in homo-and copolymer blends which are beyond the rendom phase approximation (RPA). The radius of gyration of a chain in the blend was found to depend strongly on the interactions as well as the effective diffusion constant of a single chain in the blend or copolymer melt. Note that these results cannot be obtained in the original formulation of the RPA. They are based on the effective Hamiltonian of the chain in the medium. In the equation found for the self diffusion constant of a single chain, D_s, the second term is directly the value of the effective potential at zero wave vector. Thus the measurement of D_s would detect the screened potential at q = 0. Experimental verification of these results is in progress.