Novel organized structures in mixtures of a hydrophobically modified polymer and two oppositely charged surfactants

In solutions of hydrophobically modified hydroxyethyl cellulose (HMHEC) and two oppositely charged surfactants, sodium dodecyl sulfate (SDS) and dodec yl trimethylammonium chloride (DoTAC), an organized structure of micelles h as been observed by using cryogenic temperature transmission electron micro scopy (cryo-TEM). On the cryoelectron micrographs the micelles appear to be thread on strings, arranged in a cell-like pattern. This organized structu re is induced by the polymer when the average number of polymer hydrophobic tails per mixed micelle is about 3 - 5, allowing hydrophobic tails from di fferent polymer molecules to bind to the same surfactant micelle. The organ ized structure was not observed either in the surfactant mixture alone or i n a low-viscous solution with a low number of polymer hydrophobic tails per mixed micelle. The oppositely charged surfactant mixture was studied at a total surfactant concentration of 30 mm in the presence and in the absence of 1% w/w polymer. The number of polymer hydrophobic tails per mixed micell e was varied by decreasing the micelle concentration through induced micell ar growth. The micelles grow when the mole fraction of DoTAC (X) on the SDS -rich side of the phase diagram is increased. At low X values, only micelle s are found, but from X = 0.29 upward an increasing fraction of vesicles is present. Pulsed field gradient NMR was used to measure the self-diffusion of water for determining the aggregate structure and self-diffusion of the surfactant for determining the micellar aggregation number and the concentr ation of free SDS molecules.