Complex Coacervate of Weakly Charged Polyelectrolytes: Diagram of States

The equilibrium structure of an interpolyelectrolyte complex (IPEC) coacervate consisting of weakly charged flexible polyanions and polycations with equal degree of ionization is considered. We study effects of salt concentration c(s) and solvent quality defined by second virial coefficient v on polymer density, surface tension, salt absorption, and correlations of charges and monomer units in equilibrium IPEC. Five different scaling regimes of IPEC are revealed, and a salt-solvent quality (c(s)-v) diagram of coacervate states is constructed. Boundaries between different regimes correspond to crossovers between low/high salt concentrations and poor/Theta-/good solvent conditions. Derived scaling laws for coacervate physical properties in each of regimes are in agreement with analysis based on the random phase approximation (RPA). This study summarizes and complements current theoretical comprehension of symmetrical IPEC of weakly charged polyions.