The properties of water in concentrated surfactant and colloid systems

Abstract Water is the most common component in almost all surfactant and colloid products, being present in the manufacture processes and/or the final product. Concentrated surfactants form liquid crystals with various structures (lamellar, hexagonal, cubic, etc. ) and a wide range of properties. The link between surfactant structure and liquid crystal architecture (“nanostructure”) has been established. In dilute solutions the hydrophobic effect (an entropic mechanism) underpins the formation of micelles, the building blocks of liquid crystals. Water next to hydrocarbon chains is at lower entropy due to sampling a reduced number of configurations compared to bulk water. In the past, explanations of this entropy decrease have invoked layers of “structured water” which are not supported by experiment. Liquid crystals have long-range ordered structures as with conventional crystals (solids). The nuclear magnetic resonance (NMR) spectra of non-cubic liquid crystals exhibit multiple transitions (quadrupole splittings) which reflect the mobility and degree of ordering of water and ions. Measurements on both ionic and non-ionic surfactants show three different states of water: free, bound and “disrupted”. A simple model predicts that the amount of bound water passes through a maximum with increasing surfactant concentration. Counter intuitively, at very high surfactant concentrations there is an increase in free water levels.