This is the fourth in the Science for Formulator series of related to silicone polymers (1-3). This article will deal with emulsions in general and the subsequent article will deal with the specific properties of 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 (4). 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 (4). This means that consumer acceptance comes in large part by getting the aesthetics of the emulsifier used in the formulation right.
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.
Ken Klein (5), a pioneer in the technology of emulsions, defined an emulsion as “a system of two (or more) immiscible materials (usually liquids) in which one material (the dispersed/internal phase) is suspended or dispersed throughout another material (the continuous/external phase) in separate droplets”. After having said this, Ken points out the admonition offered by Graham Barker (6) another pioneer in the technology of emulsions, warned: “All emulsions are inherently unstable (with the exception of spontaneously forming micro emulsions). All we can do is delay the ...