Abstract
The partitioning of SDS and CTAB in o/w emulsions was investigated by ultrafiltration (UF), dialysis and small-angle neutron scattering (SANS). It was possible to measure the monomeric and the micellar concentrations of the emulsifiers in the filtrate and permeate in the UF and dialysis experiments, respectively. In addition, the interfacial concentration was calculated as the difference to the initial concentration. SANS experiments provided data, from which the micellar concentrations were obtained, followed by the calculation of the interfacial concentrations. The three methods were compared on the basis of the area, which is occupied by each emulsifier molecule at the interface. Good agreement was shown for both emulsifiers studied. Micellation started at total emulsifier concentrations of approx. 10 mM in emulsions containing either CTAB or SDS. At saturation (>10 mM SDS in a 10% o/w emulsion), the area per SDS headgroup at the interface was between 48 and 64 Å2, depending on the method. In emulsions with CTAB, saturation of the interface was not achieved. The minimum headgroup area was determined by UF to be 33 Å2 at a concentration of 30 mM CTAB in a 10% o/w emulsion.
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