Effects of nonionic surfactant and sodium dodecyl sulfate layers on electroacoustics of hexadecane/water emulsions

Hexadecane-in-water emulsion droplets were formed ill a homogeniser in the presence of a mixture of an anionic surfactant (sodium dodecyl sulfate, SDS ) and nonionic surfactants of various chain lengths [nonylphenol ethoxylate (C-9 phi E-N, N = 100, 40 and 30) or an alcohol ethoxylate (Brij35)]. The dynamic mobility of the oil droplets was then measured using a flow-through version of an AcoustoSizer. Large changes were observed in the dynamic mob ility of the particles formed with the mixed surfactants compared to partic les formed with SDS alone. O'Brien's "gel layer" model was employed to inte rpret the data. The characteristics of the adsorbed layer appeared to be si milar whether the nonionic surfactant was adsorbed concurrently with the SD S as the emulsion formed or was merely added afterwards to the emulsion est ablished. The particle size, the charge and the molar fraction of SDS had v irtually no effect. The layers formed with the nonionic surfactants decreas ed in thickness with decreasing molecular weight as expected. Passage throu gh the homogeniser itself had no effect on the properties of the largest no nionic surfactant and, hence, on the adsorption layer formed with it.