Electron spin-echo modulation of x-doxylstearic acid in nonionic surfactants

Electron spin-echo studies have been carried out for a series of x-doxylstearic acid spin probes (x-DSA, x = 5, 7, 10, 12, and 16) in frozen micellar solutions of some poly(ethylene oxide) surfactants, C12E6, C12E8, C8E6, and C8E8, and in surfactants selectively deuterated along the aliphatic chain or in the poly(ethylene oxide) groups, (CD)12E6, C12D6, C8D6, and (CD)12E8, in D2O and H2O. Modulation effects due to interactions of nitroxide groups with water deuteriums or deuteriums of deuterated surfactants have been measured as a function of x. The probes are mainly located in the micelle ethylene oxide region. The average probe location in the micelle as a function of x is reported. The results obtained show that no water penetration inside the micelle core and little water penetration into the ethylene oxide region are present and do not support the current view of a fully hydrated ethylene oxide chain. It is found that only one or two ethylene oxide groups are hydrated. © 1989 American Chemical Society.