INTERACTIONS BETWEEN POLYSOAPS AND SURFACTANTS IN AQUEOUS-SOLUTIONS

Viscosity measurements and cryo transmission electron microscopy (cryo-TEM) were used to investigate the interaction between the polysoap poly(disodium maleate-co-hexadecyl vinyl ether) and two nonionic surfactants, the hexaethylene glycol monodecyl and monododecyl ethers (C(10)E(6) and C(12)E(6)). In addition, measurements of self-diffusion coefficient of the dodecyl sulfate ion in the polysoap/sodium dodecyl sulfate (SDS) system were performed to determine the amount of surfactant bound to the polysoap. The viscosity of the polysoap solutions decreases and in concentrated solutions the viscoelasticity disappears, upon addition of surfactant. Cryo-TEM shows that the long threadlike micelles, formed by end-to-end linking of polysoap chains, initially present in the polysoap solutions, progressively break up into the individual polysoap chains upon addition of surfactant. This break up is essentially completed at a molar concentration ratio R = [C(10)E(6)]/[polysoap] of about 0.2. In this respect, the nonionic surfactants used appeared to be much more efficient that the anionic surfactant SDS, that requires a ratio R of about 1.3 to achieve the same effect on the polysoap micelles. Measurements of the self-diffusion coefficient of the dodecyl sulfate ion in the presence of polysoap showed that this difference mostly arises from the fact that only a relatively small fraction of the added SDS binds to the polysoap. The binding of the added surfactant to the microdomains at the junctions between polysoap chains explains their dramatic effect on polysoap micelles at relatively low concentration of added surfactant.