COMPARING THE SURFACE CHEMICAL-PROPERTIES AND THE EFFECT OF SALTS ON THE CLOUD POINT OF A CONVENTIONAL NONIONIC SURFACTANT, OCTOXYNOL-9 (TRITON X-100), AND OF ITS OLIGOMER, TYLOXAPOL (TRITON WR-1339)

The surface-chemical properties, critical micelle concentrations (CMC) , and effect of salts on the cloud points (CP) of octoxynol 9 (Triton X-100) and tyloxapol (Triton WR-1339) were compared. The latter nonion ic surfactant is essentially a heptamer of the former. Even though the molecular weight of tyloxapol is 7 times larger than that of octoxyno l 9, its area per molecule adsorbed at the air-water interface is only twice as large. This suggests an unusual orientation for molecules of tyloxapol at the surface and is in keeping with a plateau that is les s horizontal and has a somewhat higher surface tension than the platea us of most nonionic surfactants. The CMC of octoxynol 9 was 4.4 times larger than that of tyloxapol. Unexpectedly, the CP of dilute aqueous tyloxapol solutions was 28 degrees C higher than that of octoxynol 9 s olutions. The salting-out ions Na+ Cl- and SO42- lowered the CP of tyl oxapol 29% more than that of octoxynol 9. However, because the blank t yloxapol solution started out with a higher CP value, its CPs in the p resence of salts were higher than those of octoxynol 9. Pb2+ and Mg2cations salted both surfactants in, raising their CP, Pb2+ more extens ively than Mg2+. (C) 1998 Academic Press