Highly Concentrated Cubic-Phase Emulsions: Basic Study on D-Phase Emulsification using Isotropic Gels

Abstract

In a hydrophilic octaethylene glycol dodecyl ether (C₁₂EO₈)-water system, a micellar cubic phase is formed below 20°C. Upon addition of decane, the maximum temperature of micellar cubic phase (I₁) is increased, and, moreover, the hexagonal liquid crystal region changes to the I₁ phase. Beyond the solubilization limit of decane in the I₁ phase, highly viscous and gel-like O/I₁-emulsions are formed in the two-phase region of I₁+O. In the case of a surfactant mixture (C₁₂EO_4.8) containing C₁₂EO₈+C₁₂EO₃, a single I₁ phase region is not present in a pseudo ternary phase diagram of water/C₁₂EO_4.8/decane system, but an I₁+O region appears in the oil-rich region. C₁₂EO_4.8 forms lamellar liquid crystal in the aqueous system but C₁₂EO₃ in the mixture is dissolved in oil and the mixing fraction of C₁₂EO₈ in the surfactant aggregate increases as oil is added. Finally, a two-phase region of I₁+O appears. It is considered that the O/I₁-emulsion or gel based on the cubic phase corresponds to the gel appeared in the so-called D-phase emulsification process. Upon addition of alkyl polyol such as glycerol or 1,3-butanediol, the transparency of the emulsion in the I₁+O region increases because the difference in refractive index between the cubic phase and excess oil is decreased. The maximum temperature of the I₁ phase decreases with increasing polyol content. Consequently, the addition of alky polyols is not crucial to form O/I₁ gels in an oil-rich region.