42 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 2000- lOOO- - 125 - 100- 7õ- 25 • I I I I I ! 1% _- I • c.•.c. ! - o.•1 O.Ol o.1 1.o lO.O SDS CONCENTRATION % Figure 14. Relative viscosity of 1% polyquaternium 10 as a function of added SDS concentration (47). (47). The most likely explanation is that "super macromolecules" are formed through association of the alkyl groups of surfactant ions bound to different polymer molecules. Such a structure would have pronounced shear thinning characteristics, and this was confirmed: at a shear rate of 100 sec-• the system had thinned to the consistency of the uncrosslinked state. Opportunities for rheology control are clearly provided. It should be mentioned that thickening effects on addition of surfactant are dependent on the structure of the polyelectrolyte. Thus the much more flexible polycation, polyquater- nium 5, based on vinyl chemistry, did not show the viscosity increase displayed by the "stiff" cationic cellulosic/SDS combination. Of course, the effects observed would be expected to depend on the concentration of the polyelectrolyte employed, and this pa- rameter, as well as the ratio of surfactant to polymer, would need to be examined for each system. [Other indicators of alteration in structure and conformation of polyions on association with surfactant include changes in small-angle neutron scattering (47), and in optical rotatory dispersion (48) if the polyion is optically active.] As seen in Figure 14, in the post-precipitation range, viscosity tends to drop, reflecting changes in configuration of the macromolecules. Some unusual dependencies on shear rate of the viscosity have been reported in this region for PQ-10/SDS mixtures (47). [We should point out that synergistic viscosity effects have been reported (49) for polyion/surfactant mixtures of like charge, viz., cross-linked polyacrylate plus TEALS. Coacervation phe- nomena are thought (49) to be involved at the high concentrations of surfactant em- ployed].

POLYMER/SURFACTANT INTERACTION 43 SOLUBILIZATION Micellar surfactant solutions are well known for their ability to dissolve oil-soluble materials, e.g., dyes, hydrocarbons, esters, perfumes, and so on. To the extent that complex formation with a nonionized polymer can be regarded as a depression of the aggregation concentration of the surfactant (i.e., T• • CMC), enhanced solubilization by the complex can be anticipated. This effect has been confirmed using water-insoluble dyes (8,50,51) and sparingly soluble fluorescers (52). Much more pronounced effects have been found for polyelectrolyte/ionic surfactant pairs. For the cationic cellulosic/ SDS pair, a solubilization region for the dye, orange OT, occurs at very low concentra- tion, and the "main" solubilization zone is also widened (shifted to lower concentration) as compared to simple SDS solutions (47). (See Figure 15.) Since polymers and surfactants can associate in solution, it would not be surprising if they could influence each other's solubility as well as that of a third component. Perhaps the best known case of this effect was reported by Isemura and Imanishi (53), who showed that a PVAc polymer of very low solubility could be solubilized in solutions of SDS. Another specific case of solubilization of polymers by surfactants is treated in the next section. In an interacting nonionized polymer/ionic surfactant pair, it is logical to expect that increased solubility could be manifested in the opposite sense, i.e., the polymer could increase the solubility of the surfactant since the monomer concentration required for aggregation of the surfactant is lowered in the presence of the polymer. Such an effect has, in fact, been reported by Schwuger and Lange, who showed that PVP can reduce the Krafft point of sodium hexadecyl sulfate by close to 10øC (9). Note: It is well known that many conditioning polymers are polycationic, and we have pointed out that precipitation zones exist at certain ratios in combinations of such polyelectrolytes with anionic surfactants. In most cases, however, such precipitates can 3.0 SDS/O.1% m• 2.0 1.O S O O.010 0.020 SDS CONCENTRATION (MOLES/LITER) Figure 15. $olubilizarion ooe o•angc OT by SDS a]onc aria in •hc p•cscncc o• 0. [% polyq•cmi• •0 (47).