SMALL-ANGLE NEUTRON-SCATTERING STUDY OF IONIC NONIONIC MIXED MICELLES

We studied mixtures of a ionic amphiphile, sodium dodecyl sulfate (SDS), and of a nonionic amphiphile, beta-dodecylmaltoside (DM), in D2O. From the measured dependence of the scattered neutron intensity on the scattering angle, we derive the aggregation number and the electric charge Z of the mixed micelle at various compositions and ionic strengths. We find that Z is very weakly dependent on the micelle composition when the fraction of nonionic amphiphile X is below 80% and coincides with the structural charge when 0.8 < X < 1. The results obtained in the absence of salt are in agreement with theoretical predictions of counterion condensation on spherical polyions.