Adhesion of emulsified oil droplets to hydrophilic and hydrophobic surfaces - effect of surfactant charge, surfactant concentration and ionic strength.

Adhesion of emulsified oil droplets to a surface plays an important role in processes such as crossflow membrane filtration, where the oil causes fouling. We present a novel technique, in which we study oil droplets on a model surface in a flow cell under shear force to determine the adhesive force between droplets and surface. We prepared an emulsion of hexadecane and used hydrophilic and hydrophobic glass slides as model surfaces. Different surfactants were used as emulsifiers: negatively charged sodium dodecyl sulphate (SDS), positively charged hexadecyltrimethylammonium bromide (CTAB) and nonionic Triton X-100. We evaluate the role of the surfactant, the glass surface properties and the ionic strength of the emulsion. We found a minimum in the adhesion force between droplets and surface as a function of surfactant concentration. The charged surfactants cause a lower droplet adhesion compared to the nonionic surfactant. The flow cell technique presented here proved to be very useful in understanding the interaction between oil droplets and a surface.