Phase separation in solutions of polyelectrolyte complexes: The decisive effect of a host polyion

Abstract

Boundaries of the existence of insoluble polyelectrolyte complexes in solutions of nonequimolar mixtures of quaternary polyamines and polycarboxylates of various degrees of polymerization have been determined with turbidimetric titration. It has been shown that in salt-free media the position of critical points expressed as the ratio between the charge numbers of polymer components in a mixture depends on the chemical nature of the host polyelectrolyte (polycation or polyanion) but does not depend on either the nature of the guest polyelectrolyte or the degree of polymerization of mixture components. Upon addition of a low-molecular-mass polyelectrolyte, the heterogeneous region widens. The shorter the host polyelectrolyte relative to the guest polyelectrolyte, the more pronounced this effect. Based on the thermodynamic state of the systems under examination, an explanation of this effect is confirmed by the velocity sedimentation data.