The importance of knowing what type of emulsion tcchandran and khan101 are referring to, can be exemplified by a typical W/O emulsion as it occurs during normal operation of IC engines.
In addition to the primary functions of lubrication, oils must also contend with various combustion products, mainly acidic gases, moisture, metallic catalysts, oxygen, partly oxidized chemicals and carbon particles. For this reason dispersant and detergent additives are formulated with the lube. Unfortunately, these and other additives, such as VI improvers, act as surfactants having a stabilising effect on foams and emulsions that may form under the high shear regime.
Typical demulsifiers for these W/O type of emulsions comprise more than one component, that must be attracted to the interface and have limited solubility in the bulk phase. Their greater affinity to the water-oil interface ensures that the stabilising molecules are displaced.
Another important feature they exhibit is a reduced inter-droplet repulsion, allowing the droplets to aggregate. The final demulsifying stage is typified by a decrease in interfacial tension and surface area. Apart from good filtration to remove the resulting concentrated solid and debris, stubborn emulsions require the application of a chemical at the final film-rupture stage.
It has been said that the skill of formulating a demulsifier is a "black art". In effect, the selection of an effective demulsifier relies on a "trial and error" approach, suplemented by some
knowledge of what has worked before.
The rate of water coalescence is taken as a measure of the effectivenes of the product. Almost every class of surfactant has been found to exhibit demulsification properties.
The most commonly used products in motor oil formulations contain anionic surfactants (e.g. alkyl naphthalene sulphonates) and nonionic surfactants such as alkoxylated alkyl phenol resins and block copolymers of ethylene oxide and propylene oxide.
![[smile] [smile] [smile]](/data/assets/smilies/smile.gif)