Phase behaviour of surfactants and its effect

Most of the recent research work has been carried out by using pure model systems, which are very far from the real complex systems used in product formulations. However, these model studies are unable to predict the actual product properties. The objective of this article is to describe the application of some of the structural knowledge of the phase behaviour of soaps and surfactants in understanding the mechanism of formulations, processes and product attributes. This article covers the mechanism and the practical application of the main liquid and solid phases. In addition to processing conditions, other parameters such as carbon chains, functional groups and level of moisture have a large impact on the formation of these phases. Furthermore, it is important to know the significance of Krafft Point in understanding the structural aspects of soaps and surfactants. Therefore, any physicochemical change affecting the Krafft Point has a profound effect on the formation of different phases which in turn affects the product properties. Surfactants play a very important role in our day-to-day life. From morning until evening we come across a lot of products which contain surfactants at different levels. Toothpaste, bar soaps, shampoos, liquid soaps, shower gels, dish wash, fabric washing powders, fabric washing liquids, floor cleaners, car wash etc. are some of the products where surfactants are used for foaming and cleansing purposes. Creams, lotions, hair treatment, conditioners and other skin care products contain surfactants as emulsifiers to keep the product stable. Liquid fertilisers, insecticides, some medicines and food products also need surfactants as stabilisers. All these products are available in different forms such as solids, gels, liquids or pastes. Different forms of products require surfactants with different physicochemical properties, suitable for the particular product. These physicochemical properties are highly affected by the molecular structure of the surfactants.

Molecular structure

Surfactant molecules have a unique molecular structure which gives special physical properties to the surfactants. Surfactants have both hydrophilic and hydrophobic groups present on the same molecule. These types of molecules are called amphiphilic. Because of the opposing nature of the two groups, when dissolved in aqueous or non-aqueous mediums, these molecules behave in a very different way. A good analogy to show the behaviour of surfactant molecules can be the example of tug-of-war, where two opposing groups pull the rope and depending upon the strength of the groups ultimately one of the groups succeeds in pulling the rope. Similarly, once surfactant molecules are dispersed in water then there is a competition between the two opposing groups. The hydrophilic group tends to move towards the aqueous phase while the hydrophobic group keeps itself away from it.