Lower critical solution temperature (LCST) and theta temperature of aqueous solutions of nonionic surface active agents of various polyoxyethylene chain lengths

1435-1536

Lower critical solution temperature ; theta temperature ; nonionic surfactant ; conformation of polyoxyethylene chain ; phase separation

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Cloud points of aqueous solutions of homogeneous poly(oxyethylene)dodecyl ether derivatives (C12(OE)n: n=2–8) and the apparent theta temperatureTθ ap were determined from the abrupt changes in optical transmittance and the temperature dependence of the second virial coefficient obtained by light scattering measurements. It was found that the lower critical solution temperature (LCST) shifts to a lower temperature and lower concentration as the number of oxyethylene units in a molecule decreases. Because of this behavior of LCST, the modified Flory-Schultz plot of phase separation was applied to the present nonionic surfactant-water system, and its theta temperature obtained. The dependence ofTθ ap on the number of oxyethylene units suggests that the polyoxyethylene chain has different effects on the solubility of C12(OE)n in water forn less than or equal to 3 from those forn greater than or equal to 4.

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