MIXED MICELLES OF DODECYLTRIMETHYLAMMONIUM BROMIDE AND DIDODECYLDIMETHYLAMMONIUM BROMIDE

Mixed micelles of dodecyltrimethylammonium bromide (DTAB) and didodecy ldimethylammonium bromide (DDAB) are investigated with small-angle neu tron scattering (SANS). The roughly spherical DTAB micelle elongates, and the fraction of condensed bromide ions increases, as the DDAB-DTAB mixing ratio increases at a constant total surfactant concentration. The aggregate composition matches that predicted by an ideal mixing mo del. SANS contrast variation experiments using partially deuterated DT AB (DdTAB) confirm the modeling parameters determined from fully hydro genated surfactant samples and provide consistent structural informati on about the interfacial region.