OIL-IN-WATER EMULSIONS

The challenges that are present in the current development of oil-in-water (O/W) emulsions are the increased use of silicone and silicone polymers in these types of formulation. Generally speaking, many of the silicone ‘oils’, polymers and elastomers have very poor compatibility with typical organic ‘oils’ or esters. The challenge is in the selection of the emulsifier system and the combination of hydrophobic materials that will allow for a homogeneous and uniform internal oil phase. In addition, this phase is also a delivery system for a number of functional ‘active’ ingredients, enhancing their functionality and performance.

The choice of ingredients now needs to consider the effect on performance as well as aesthetics. Figure 3.1 is an O/W emulsion in which the predominant components of the oil phase are a blend of silicones. This emulsion can be modified with the addition of bioactive ingredients—antioxidants and skin-soothing ingredients. The other aspect of this formulation that is worth noting is the use of an emulsion-stabilizing system that can be added at the end. This ingredient serves a dual function—adjusting viscosity and improving emulsion stability. Care must be taken, however, because these emulsion-stabilizing systems can also affect the feel of the product.

Fig. 3.1 An oil-in-water (O/W) emulsion

WATER-IN-OIL AND WATER-IN-SILICONE EMULSIONS

Water-in-oil (W/O) and water-in-silicone (W/S) emulsions, sometimes referred to as ‘inverse emulsions’, are formulations in which the internal or dispersed phase is a water phase, and the oil (or silicone) phase is the continuous or external phase. While still much less popular than O/W emulsions, recent advances in silicone-based emulsifier systems have caused an increase interest in these types of formulation. The formulation from Dow Corning (Fig. 3.2) demonstrates the use of these newer emulsifier systems. They have become increasingly useful when developing water-resistant sunscreen products and when looking to incorporate more lipophilic (oil-loving) functional materials into formulations that deliver skin care benefits such as barrier protection. The formulation of ‘inverse emulsions’ has been extended to where the internal phase is a hydrophilic polyol in place of water. The formulation from Momentive (Fig. 3.3) is an example of an ‘anhydrous’ emulsion which can be used as a delivery system for cosmeceutical ‘actives’ that have stability issues in water (i.e. ascorbic acid—vitamin C).

Fig. 3.2 Emulsifier system

Fig. 3.3 An anhydrous emulsion.

(Reproduced with permission from Momentive, Wilton, CT.)