The self-assembly behaviour of oppositely charged polyelectrolyte surfactant complexes (PESCs) is very rich and quite a number of structurally different arrangements such as pearl-necklace structures, rodlike aggregates, uni- or multilamellar vesicles has been reported. Aside from fundamental scientific interest, PESCs have found application in cosmetics, detergency and enhanced oil recovery EOR. Some PESCs show a remarkable increase in viscosity near charge equilibrium, while other very similar systems do not show any appreciable effect. The exact structural prerequisites to achieve a significant increase in viscosity are still unclear. Here, we study PESCs consisting of the cationic polydiallyldimethylammonium chloride (PDADMAC) and sodium dodecylsulfate (SDS) and compare the results to the previously investigated PESCs of SDS and the cationically modified hydroxyethyl cellulose (JR 400). Under similar conditions, PDADMAC based PESCs do not significantly increase the viscosity of solutions, as was observed for JR 400. The observed differences in the macroscopic viscosity were linked to the differences in the mesoscopic structure, explicitly confirmed by the small angle neutron scattering (SANS), and in the dynamics of the polyelectrolyte chains, confirmed by the neutron spin-echo spectroscopy (NSE). While JR 400/SDS PESC forms an interdigitated complex structure, PDADMAC/SDS favours the formation of a segregated core-shell structure. The latter one is having significantly less strong anchoring of the polyelectrolyte to the complex, hence PDADMAC chains possess much higher dynamics, resulting in a much less pronounced increase in viscosity.

Viscosity of polyelectrolyte surfactant complexes (PESCs) – the importance of the choice of polyelectrolyte seen for the case of PDADMAC vs. JR 400

ACS Fall 2021

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