The term surfactant comes from surface active agent1 (SURFace ACTive ageNT). The most basic definition of a surfactant is molecule that has two covalently linked groups that would be insoluble in each other in pure form.2 Surfactants are usually organic compounds that are amphiphilic, meaning they contain both hydrophobic groups (their tails) and hydrophilic groups (their heads).3 Heretofore, a surfactant was defined as containing both a water-insoluble (or oilsoluble) component and a water-soluble component. Dr Rosen has spent his career as the ‘Father of Surfactants’, working primarily in a field of water and oil based surfactants. His classical book Surfactants and Interfacial Phenomonen4 now in the fourth edition, provides a ‘roadmap’ to study all types of surfactants.  This roadmap has been found to apply extremely well to surfactants that do not contain either water or oil soluble groups.


Figure 1 shows a beaker containing water, dimethicone (350 visc) and mineral oil. As can be plainly seen, these three are mutually insoluble. 


First, take a moment to review some terms: Oleophilic refers to materials that ‘love’ oil. These materials are ‘water insoluble’ and therefore are hydrophobic. In a simple two-dimensional world of just oil and water, any material that ‘loves’ oil ‘hates’ water. The problem is that cosmetic chemists live in a three-dimensional world. This additional dimension is silicone. Silicone is insoluble in oil and water. Table 1 shows these terms.5,6 Siliphilic refers to a material that is water insoluble (hydrophobic) and oil soluble (oleophilic). It is therefore referred to as siliphilic.  


Why is this important? Many pigments are coated to make them hydrophobic (water-hating). The hydrophobic coating can be oil (oleic acid, for example) or silicone (dimethicone, for example). If the coating is silicone, the pigment is siliphilic. If the coating is oil, the pigment is oleophilic. The selection of the proper non-aqueous phase and the nature of the emulsifier needs to be made to maximise stability