PHASE-BEHAVIOR OF A NONIONIC MICROEMULSION UPON ADDITION OF HYDROPHOBICALLY-MODIFIED POLYELECTROLYTE

We report on the effects on the phase behavior in the water-rich part of the ternary nonionic surfactant system, pentaethylene glycol dodecy l ether (C(12)E(5))-water-decane, when adding sodium polyacrylate (PA) or hydrophobically modified polyacrylate (HMPA). The polyelectrolytes , having the same degree of polymerization, were derived from polyacry lic acid of M(w) = 150 000. The HMPA contains hydrophobic octadecyl si de chains randomly anchored to the polyelectrolyte backbone, with a de gree of modification of either 1 or 3% of the monomer units. The PA is found to be insoluble in the lamellar liquid crystalline and the liqu id L(3) phases, containing infinite bilayer aggregates, while it is so luble in the liquid L(1) phase containing oil-swollen normal micelles. The HMPA, on the other hand, can be solubilized in all three phases, however, strongly affecting the phase equilibria. From the difference it is concluded that while PA is nonadsorbing, HMPA adsorbs to the sur factant film by the hydrophobic ''stickers''. In the presence of HMPA the surfactant films behave as effectively charged with long-range ele ctrostatic interactions and a positive shift of the spontaneous mean c urvature. The lamellar phase containing the HMPA phase separates at hi gher bilayer concentrations into two lamellar phases in equilibrium. H ere a HMPA-rich lamellar phase with larger water spacings coexists wit h a lamellar phase of smaller water spacings essentially free of HMPA.