Low viscous oil-in-water (o/w) emulsions are of interest for many cosmetic applications. Systems of particular interest are sprayable emulsions (see Sprayable Emulsions sidebar) and impregnating lotions, such as those discussed in this article, for the preparation of cosmetic lotion wipes. In order to combine low-emulsion viscosity and good storage stability, a very fine droplet size is needed. This article describes a cold process using non-ethoxylated emulsifiers for preparing o/w emulsions with low viscosity, very fine droplet size and good storage stability.
Finely dispersed emulsion droplets do not undergo sedimentation or creaming because these processes are prevented by the Brownian motion of such small droplets. The submicroscopically small oil droplets cause a characteristic blue shining appearance of these emulsion systems.
A common process for the preparation of such blue shining emulsions is the phase inversion temperature (PIT) method. The PIT method makes use of the low interfacial tension that is obtained in the region of phase inversion from a water-in-oil (w/o) to an o/w emulsion upon cooling; normally a microemulsion or a lamellar phase is passed in the phase inversion temperature region. This low interfacial tension in the phase inversion region allows the spontaneous formation of finely dispersed, blue shining o/w emulsions (PIT emulsions). Nonionic ethoxylated emulsifiers are known for their strongly increasing hydrophobicity with increasing temperature, which is the reason why all practical applications of PIT emulsions are based on the use of ethoxylated emulsifiers.
Recently, personal care applications have shown a trend toward more natural ingredients. Therefore it was challenging to develop an alternative to the PIT technology based on emulsifiers that are non-ethoxylated (PEG-free). Additionally, and especially with regard to the production of cosmetic lotion wipes, such a new technology should ideally be easy to process without the need to use a homogenizer or heating.
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