THE SPIN PROBE-SENSED POLARITY OF SODIUM DODECYL-SULFATE MICELLES IS PROPORTIONAL TO THE 1/4 POWER OF THE SURFACTANT CONCENTRATION

The polarity of sodium dodecyl sulfate micelles, as reported by the isotropic N-14 hyperfine coupling constant, A0, of a spin probe is shown to be proportional to the one-fourth power of the surfactant concentration in the range 25-200 mM. Coupled with a recent finding that the aggregation number of these micelles shows the same dependence, suggests the working hypothesis that the polarity is proportional to the aggregation number. Using this hypothesis, these measurements show that EPR has the potential to distinguish relative aggregation numbers with a precision of about one molecule per micelle. Polydispersity does not affect EPR lineshapes in most cases.