US EPA

3767606 

Journal Article 

DISTINCTIVE BEHAVIOR OF THE ESR CORRELATION TIMES OF DOXYL SPIN PROBES IN MIXED MICELLAR SOLUTIONS OF HYDROCARBON AND FLUOROCARBON SURFACTANTS 

Kamogawa, K; Tajima, K 

1993 

1 

Journal of Physical Chemistry
ISSN: 0022-3654 

97 

37 

9506-9512 

10.1021/j100139a040 

WOS:A1993LY47200040 

The ESR correlation time tau(c) of DOXYL stearic acid nitroxide spin probes was measured to clarify the micellar miscibility of perfluorocarbon and hydrocarbon surfactants in an aqueous solution. In one group, named type I micelles, tau(c) was found to increase on mixing at first and then decrease at a particular composition. An invariant region separated such a change in tau(c) for another group, named type II micelles. The two types were consistent with the freely miscible, and the partially immiscible, micelles following Shinoda's theory (J. Phys. Chem. 1980, 84, 365-369). Sodium perfluorooctanoate and sodium dodecyl sulfate at 45-100 mM concentration formed type I micelles. The tau(c) profile converted to type II behavior in the presence of 0.1 M NaCl. Ammonium perfluorononanoate and ammonium dodecyl sulfate also exhibited type II behavior at 25-degrees-C, accompanied by a discontinuous jump in tau(c) at X(HC) = 0.65. The invariant region disappeared at 50-degrees-C leading to type I profile, as predicted theoretically. Prior to this conversion, the jump of tau(c) disappeared at 40-degrees-C. In an Arrhenius plot, the logarithm Of tau(c)-1 for X(HC) = 0.7 and 1 both gave parallel, monotonic decreases with T-1, though that for X(HC) = 0. 5 coincided first with the line for X(HC) = 0. 7 but appeared a transition at 40-degrees-C to the X(HC) = 1 line. These characteristics were discussed in relation to standard 2-micelle models and a new 1-micelle model.