Influence of Gel Networks in Controlling Consistency of O/W Emulsions Stabilised by Mixed Emulsifiers

Abstract

A coherent explanation is presented of the mechanisms by which mixed emulsifiers of the surfactant/fatty alcohol type both stabilise and control the consistencies of oil‐in‐water emulsions. Original and published data are used to develop a theory in which the semisolid and other flow properties of emulsions are related to the nature, strength and extent of viscoelastic networks present in the continuous phases. These networks form from the interaction of surfactant solution with fatty alcohol and have similar properties to ternary system gels formed when the mixed emulsifiers disperse in water, in the absence of an oil. The theory is discussed with particular reference to liquid paraffin‐in‐water emulsions prepared with the surfactants anionic sodium dodecyl sulphate, cationic alkyltrimethylammonium bromides or non‐ionic cetomacrogol and fatty alcohols cetyl and stearyl and their mixtures, especially cetostearyl. It may be used also to explain the properties of emulsions prepared with a variety of oils, surfactants and amphiphiles. The effects of variation in storage time, surfactant type (ionic or non‐ionic), temperature, mixed emulsifier concentration, and alcohol and surfactant chain lengths on the rheological and microscopical properties of ternary systems and emulsions support this theory. The importance of small strain experiments (creep and oscillatory) in providing a true measure of consistency is emphasized. Continuous shear experiments, although theoretically less satisfactory, provide useful additional information when correlated with the small strain data.

Gelled emulsions with a high water content

“…In this respect this emulsion is different from earlier ones with liquid crystals [2][3][4][5][6][7][8][9][10][11][12]. These have shown thick liquid crystalline layers with inhomogeneous spreading around the emulsion droplets and also macroscopic droplets of liquid crystal in the continuous phase.…”

“…It appears obvious that this gel system owes its features to different phenomena than those found in the traditional gel systems [1][2][3]. We found an investigation intothe structure of this gel well justified, against the fact that its extremely low surfactant content gives it an advantage over other systems.…”

“…Gels applied in cosmetics [1] usually contain surfactants at concentration levels of several percent and the gel properties are obtained from a dispersion of a liquid crystalline phase, as discussed by Barry [2,3]. However, recent results from the Institute for Chemical Technology and Textiles in Spain [14,16] demonstrated a gel system with surfactant concentration of only 0.5 0/0 be weight.…”

Hydrophilic Ionic Liquids as Ingredients of Gel-Based Dermal Formulations

“…Furthermore, the ILs can be used as solvents for pharmaceutical components (30) and choline salts can be useful for stabilization of protein-based APIs in the formulation (31 Formulations that included SEPINEO™ P 600 resulted in high-viscosity gels or emulsion-gels. Addition of cetylstearyl alcohol as an additional thickener led to a slight increase in viscosity, in comparison to the formulation without cetylstearyl alcohol, due to the formation of a liquid crystalline phase (32). A further increase in viscosity was observed after adding mediumchain triglycerides or paraffin oil as an oil phase.…”

Phase behavior of fatty acid/oil/water systems: Effect of the alkyl length chain acid

“…These molecules may self-assemble into a variety of aggregates ranging from micelles to bilayers and lamellar multilayers or other forms of liquid crystalline structures (1)(2)(3).…”