DYNAMIC SCATTERING FROM MIXTURES OF WEAKLY CHARGED POLYMERS

The dynamic scattering properties of mixtures of weakly charged polymers are investigated. The case of ternary mixtures of two charged polymers in solution is studied in detail. The time evolutions of the partial dynamic correlation functions are examined starting from the matrix equation S(q,t) = partial (-0t)S(q), where S(q) is the static structure matrix and OMEGA is the first-cumulant matrix. This quantity is expressed in terms of S(q) and the mobility matrix M(q) as OMEGA = q2kTM(q)-S-1(q). The eigenvalues of OMEGA as well as other relevant relaxation frequencies are investigated in detail at various conditions of charge distribution. The model used here is based on three approximations: (i) an extension of the random phase approximation (RPA) to include the long-range electrostatic interaction in the calculation of the static structure matrix S(q), (ii) the Debye-Huckel approximation to describe the effects of Coulomb forces between charged particles, and (iii) the Rouse limit for chain dynamics. Furthermore, the small ions such as counterions and co-ions are assumed to be point particles, their dynamics is not accounted for explicitly, and, therefore, only the apparent diffusion of macroions is described.