Review of silicone emulsifier selection
This is the fifth in the Science for Formulator series of related to silicone polymers (1-4). This article will deal with emulsions made using silicone based emulsifiers. Despite the large number of chemical classes of silicone polymers, there are several specific functional attributes that make silicone interesting in polymers used in personal care. It is these functional attributes of silicone, which are a direct result of their structure that is being examined in this series of articles. As formulators, we use silicone polymers (1), lower surface tension to levels not achievable with fatty based surfactants (2), provide outstanding spreadability (3), provide a highly prized aesthetic on the hair and skin and (4) are non-irritating. What is tremendously interesting in the formulation of emulsions, is not only are silicone based emulsifiers useful over the wide range of emulsion types (i.e. O/W and W/O) but recent studies indicate the emulsifier not the emollient provides 80% of the initial aesthetics to the emulsion (5). This means that consumer acceptance comes in large part by getting the aesthetics of the emulsifier used in the formulation right.
As pointed out in article 4, emulsification is a process that allows for the preparation of a metastable single phase of two insoluble materials. The preparation of cosmetically appealing emulsions is a very challenging and often frustrating undertaking. The metastable nature of the two insoluble materials is critical to understanding the nature and performance of emulsions. The metastable nature of the emulsion, and the requirement that the emulsion be cosmetically appealing, offer unique challenges to the formulator. This article will deal with the nature of the emulsion and what factors affect the emulsion. This inclusion of silicone in the emulsifier provides a silicone like feel and can tremendously modify the aesthetics of the emulsion.
The first requirement for making an emulsion is that it must be made up of at least two insoluble materials. This is due to the observation that if the two materials are soluble in each other, a solution is the result. Solutions are clear and can be prepared using any ratio of the two or more soluble liquids.
The most commonly unders ...