Influence of Ionic Surfactants on the Formation of Liquid Crystals in Oleic Acid/Glycol/Water Systems

The influence of surfactant structure on the formation of lamellar liquid crystals with very low surfactant concentration was investigated for systems composed of oleic acid, diethyleneglycol ethyl ether and water. Surfactants belonging to anionic and cationic families were checked: phosphated oleyl ether 3 EO (PO₃EO), triethanolamine oleate (TEAO) and sodium lauryl ether sulphate (SLES) as anionic surfactants and two alkyl trimethylammonium bromide type (C₁₂TAB and C₁₄TAB) as cationic surfactants. For each of the surfactants, the appropriate relationships between surfactant, oleic acid and glycol to furnish lamellar liquid crystals when these basic compositions were further diluted with water were established. The appropriate ranges of dilution allowing the liquid crystal formation were also determined. These liquid crystals presented an attractive appearance because of their transparency and high viscosity, although in the beginning of its formation, a short range of less viscous compositions (so called liquid/gel compositions) appears in some cases. Through water dilution, the initial surfactant percentages are noticeably reduced being possible liquid crystals with 2–5 wt% of surfactant.

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