SANS Studies of Octyl-β-glucoside and Glycine Micellar Solutions

Small-angle neutron scattering (SANS) experiments were performed on micellar solutions of octyl-β-glucoside (OBG) in water and on solutions of OBG + glycine in water. A detailed analysis of the results obtained for different concentrations (from 0.026 to 1 M) of glycine and OBG shows that: (i) the structure of the micelles of OBG is always ellipsoidal with the long axis increasing as the concentration of OBG increases from the critical micellar concentration (c.m.c. = 0.022 M) to 1 M; (ii) there is a tendency to form aggregates at concentrations of OBG smaller than 0.5 M; (iii) steric repulsive interactions are clearly seen for concentrations above 0.6 M. The virial coefficient is evaluated as a function of the concentration in OBG. The negative values at low concentration reveal the presence of attractive interactions, while at high concentration the repulsive steric interaction dominates. At high concentration of OBG, the spectra with or without glycine are the same. The analysis shows that glycine remains in water and that its presence does not affect the structure of the micelles.