Investigation of the film formation mechanism of oil-in-water (O/W) emulsion

To reveal the film formation mechanism of oil-in-water (O/W) emulsion, nanofilms of aqueous paraffin oil emulsion stabilized with the nonionic Tween 80 and Span 80 surfactants were measured in confinement between two solid surfaces, by the use of relative optical interference intensity (ROII) approach. In contrast to single-phase oil lubricant, the film formation of oil-in-water emulsions normally possesses a hill appearance. The critical speeds of film formation of O/W emulsions with various emulsifier and oil concentrations were focused to study the film formation mechanism of oil-in-water emulsion. Droplets can be observed to concentrate and be broken before the contact under a low speed, which induces an oily pool. The oil pool was indicated to act as the provider to the lubrication of the contact during rolling process. A theoretical model was proposed to describe the reemulsification effect, which established a relationship between the critical speed and the concentrations of either oil or emulsifiers.