Effect of the Charge Regulation Behavior of Polyelectrolytes on Their Nonequilibrium Complexation with Oppositely Charged Surfactants

The nonequilibrium features of oppositely charged macromolecule/surfactant mixtures have been the subject of intensive research recently. Although the nature and extent of polyion charge crucially affect the development of trapped states in these systems, their role in the non equilibrium association is still poorly understood. In the present study, the impact of mixing on the complexation of hexadecyltrimethylammonium bromide (CTAB) with sodium poly[(vinyl alcohol)-co-(vinyl sulfate)] (PVAS) and poly (acrylic acid) (PAA) samples of similar charge densities has been compared using a variety of experimental methods. The results indicate largely different nonequilibrium behavior depending on the polyions. In the case of the weak polyacid PAA, the binding of CTAB increases its ionization degree, which leads to enhanced equilibrium two-phase concentration range, where kinetically arrested states can be observed upon rapid mixing of the solution components. In contrast, the charge density of the double-hydrophilic PVAS copolymer is fixed, and in addition to the binding of CTAB onto its vinyl sulfate groups, the surfactant molecules also bind onto the vinyl alcohol segments of the copolymer. These factors result in reduced precipitation concentration range and diminishing nonequilibrium effects with decreasing polyion charge density. Our study clearly demonstrates that the charge regulation behavior of various polyelectrolytes can be successfully used to tune the nonequilibrium characteristics of macromolecule/surfactant association.