A SANS study on growth of anionic micelles with quaternary ammonium bromide

The micellar growth of sodium dodecyl sulphate in presence of inorganic (KBr) and quaternary ammonium bromides (R4NBr, R = C2H5 or n-C3H7) has been studied by small-angle neutron scattering measurements at 30degreesC. The data has been analysed using Hayter-Penfold model. After combining the results of previous and present studies, no direct relationship between length of alkyl part (R) and aggregation number (n(s)) of the micelles is found. It is proposed that both the inorganic and quaternary counterions (with R less than or equal to C2H5) cause. micellar growth due. to screening of micellar surface charge while latter ones (specially with longer R) do it by screening and increased hydrophobic interaction. Also, n(s) increases with increase in [R4NBr].