Sucrose esters are well-known natural emulsifiers and while they are desired for their mildness and safety, they also are relatively expensive when compared with other emulsifiers. Accordingly, they have not been used as widely as they might at lower costs. In response, the authors have developed an emulsifier system comprising a mixture of ethylene oxide-free sucrose esters used at low levelsa to improve their cost-effeciency. This blend is shown to form multi-lamellar liquid crystalline networks that impart various benefits including skin moisturization, assessed here. Further, most cosmetic compositions prepared with the blend can be formulated with minimal regard to HLB due to the emulsion stabilization provided by multilamellar liquid crystals, which minimize emulsion coalescence.
Sucrose Ester Multilamellar Emulsifiers (SEMLEs)
Pioneering theoretical work on the formation of lamellar liquid crystalline networks was conducted by Friberg and Barry in the early 1970s. According to a summary of this work, lamellar liquid crystal networks can be formed in o/w emulsions by combining a high HLB primary emulsifier such as a hydrophilic swellant with a second, low-to-medium HLB co-emulsifier, i.e., a hydrophobic gellant. The high HLB primary emulsifier reduces interfacial tension and facilitates the formation of small oil droplets in the outer aqueous phase whereas the low HLB co-emulsifier forms a gel network.
This network structure stabilizes the emulsion by preventing creaming and coalescence of the oil droplets, as well as by building viscosity. More specifically, by heating the water phase to above the melting point of the low HLB co-emulsifier, the fatty chains of the co-emulsifier parallel each other, forming a bilayer structure—i.e., a lamellar phase. When this blend is subsequently cooled below that melting point, gel networks form around the co-emulsifier fatty chains.
The described topical composition includes: an emulsifier system comprising approximately 0.2% to 1.2% w/w of a mixture of a first sucrose ester, namely sucrose monostearate, with a second sucrose ester, sucrose distearate; in addition to at least one solid fatty alcohol having a melting point of at least 45°C, wherein the ratio of monostearate to distearate is ~1/1.3. This composition was shown by polarizing photomicroscope studies to form a multilamellar liquid crystalline network.
Lab Practical: Formulating with SEMLEs
- This blend is ethylene oxide-free and thus environmental friendly.
- The material produces emulsions with sustained moisturizing effects.
- Emulsions employing the technology are water-resistant.
- The blend can be used to form hydrates that produce emulsions at RT.
- Emulsification is independent of the HLB system.
- The blend is thixotropic with a self-bodying effect.