Selecting Silicone Surfactants for Personal Care Formulations

Silicone surfactants such as a dimethicone copolyol contain hydrophobic and hydrophilic portions enabling them to lower the surface tension of water. The reduction of surface tension is a necessary first step in providing foam, emulsification, wetting and other surfactant properties. Each of these surfactant properties requires a molecule that lowers surface tension. Put another way, all molecules capable of foaming, emulsifying or wetting must be able to lower the surface tension, but not all molecules that lower surface tension provide these properties. The lowering of surface tension depends on the presence of hydrophilic and hydrophobic portions in the molecule. Additional surfactant properties depend on the structure of the molecule and its activity at the surface.

The function of dimethicone copolyol or any other silicone compound alone in aqueous solution may be of academic interest. However, it is of limited interest to a formulator because formulations are never simply water and dimethicone copolyol. The key to formulation is the interaction between the surfactants and other ingredients that alter the performance of the surfactants at the surface. There are interactions between different formulation components and understanding them and optimizing them for a given effect is key to formulation success.

This article is intended to educate cosmetic chemists in the chemistry of dimethicone copolyols and their potential effects in surfactant systems, such as shampoos or body washes. It will investigate some of the interactions between selected dimethicone copolyol compounds and a fatty surfactant and how they alter the properties of a solution or formulation. The structures of materials chosen for evaluation are shown in Figure 1. Sodium lauryl sulfate (SLS) and sodium laureth-2 sulfate (SLES-2) were chosen because they are commonly used in personal care products. Table 1 outlines the molecular weight information, the INCI name and the shorthand used to designate the compounds in this article.