POLYMER-SURFACTANT INTERACTION 29 c• LU Z Z 0.1 0.01 0.001 0.001 0 • • o:m nm _.•, o..0o o .== o . n o o - 0•/• 0 0 B 0 0 B 0 0 .'•_...0" • 0 0 0 B B 0 '"• I CMC of SDS ..---'. 0.01 0.1 1 Sodium dodecyl sulfate, % Figure 4. Pseudo-phase diagram of the system DQNNED/sodium dodecyl sulfate/water. Symbols indicate: O clear solution ß precipitate '© slight precipitate [] hazy solution [] gel ...... theoretical charge neutralization when 1 SDS adds ........ theoretical charge neutralization when 2 SDS add -- maximum precipitation observed. sition, soluble complexes, liquid coacervate, or amorphous precipitate may be formed (26). The complex phase is dependent upon polymer concentration, surfactant concen- tration, molecular weight, micelie surface charge density, polymer linear charge density, and ionic strength (26-27). A polymer concentration of 1% (w/v) was chosen to be in the region between charge neutralization and resolubilization. The purpose was to determine the critical mole fraction of SDS, Yo for binding of the mixed surfactant micelies with the cationic polymers. The results of this study (Figure 6) indicate that at concentrations of SDS • 0.15%, precipitation occurs for both Polyquaternium 10 and MQNNED mixed surfac- tant micelie complexes. The charge density on the micelies causes them to bind strongly, resulting in the onset of precipitation of the complex due to charge neutralization. At concentrations of SDS • 0.15% (YsI)s • 0.28), single-phase, clear solutions were observed. Therefore, Yct= 0.30 for the systems of Polyquaternium 10 and MQNNED- mixed surfactant micelie complexes. For DQNNED, two-phase systems exist when the concentration of SDS is between 0.50% and 0.11%. The charge density on the micelies is high enough to cause precipi- tation of the complex but not sufficiently high to resolubilize the complex. There are two distinct regions where one-phase, clear solutions exist. The first region is at high micelie charge density (1 • SDS • 0.6%) and the second region at low charge density (SDS • 0.10%). Therefore, Yc = 0.22 for this system. The first region is attributed to the resolubilization of the complex by full micelies (interpolymer-micelle complexation).

30 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1 0.1 O. 0.01 0.001 ........ 0.001 0.01 0.1 1 Sodium dodecyl sulfate, % Figure 5. Observed maximum precipitation pattern for the three systems. Symbols indicate: ...... DQNNED ........ MQNNED - Polyquaternium 10. The second region is attributed to the binding of mixed surfactant micelies within the complex, as the high percentage of Octoxynol will shield the polymer molecules from each other, resulting in intramolecular polymer-micelle complexation. At high concentrations of polymer and surfactant, Yc necessary to cause precipitation is independent of extension from the chain for a monoquaternary derivative. However, Yc appears to be influenced by the number of cationic charges on the graft, as DQNNED requires a lower micelie charge density to cause precipitation than does MQNNED. FLUORESCENCE Pyrene is a strongly hydrophobic molecule whose water solubility is very low (2-3 mM). Changes in the vibronic fine structure intensities of the pyrene fluorescence spectra result from changes in the micro-environment encountered by pyrene (28). The ratio of the I•/I 3 bands is high when pyrene is solubilized in a hydrophilic medium, whereas the I•/I 3 ratio is low for pyrene in hydrophobic medium (Figure 7). Aqueous solutions of the polymers were examined for the presence of hydrophobic domains in the polymer molecules. The I•/I 3 ratio indicates that pyrene is solubilized in a hydrophilic environ- ment (Table I). A ratio of 1.7:1 indicates that pyrene molecules reside in the solvation shell of the polymer molecules. In miceliar and macromolecule systems, pyrene is preferentially solubilized in the hy- drophobic regions, and the intensity of the I•/I 3 band ratio for pyrene in micelies should decrease (28). Pyrene fluorescence intensity in micelles of 0.10% SDS/0.90% Octoxynol and 1% Octoxynol exhibits a ratio of 1.2:1 (Table I). As the I•/I3 ratio is greater than