| Abstract
| - The structures of the mixed anionic/nonionic surfactant micelles of SDS/C12E6 and SDS/C12E8 have beenmeasured by small angle neutron scattering (SANS). The variations in the micelle aggregation number andsurface charge with composition, measured in D2O and in dilute electrolyte, 0.01 and 0.05 M NaCl, providedata on the relative roles of the surfactant headgroup steric and electrostatic interactions and their contributionsto the free energy of micellization. For the SDS/C12E8 mixture, solutions increasingly rich in C12E8 show amodest micellar growth and an increase in the surface charge. The changes with increasing electrolyteconcentration are similarly modest. In contrast, for the SDS/C12E6 mixture, solutions rich in C12E6 show amore significant increase in aggregation number. Furthermore, electrolyte has a more substantial effect onthe aggregation for the nonionic (C12E6) rich mixtures. The experimental results are discussed in the contextof estimates of the steric and electrostatic contributions to the free energy of micellization, calculated fromthe molecular thermodynamic approach. The variation in micelle surface charge is discussed in the contextof the “dressed micelle” theory for micelle ionization, and other related data.
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