Phase Behavior and Formation of Reverse Cubic Phase Based Emulsion in Water/Poly(oxyethylene) Poly(dimethylsiloxane) Surfactants/Silicone Oil Systems

Abstract

The phase behavior of long hydrophobic A−B type silicone surfactants, Me3SiO−(Me2SiO)m-2−Me2SiCH2CH2CH2−O−(CH2CH2O)nH (SimC3EOn), in water and water + octamethylcyclotetrasiloxane (D4) was investigated by studying phase behavior and small-angle X-ray scattering. Si25C3EO15.8 forms a reverse micellar cubic phase (I2) in water and water + D4 systems. This cubic phase is highly thermally stable in a surfactant−water binary system. The thermal stability decreases monotonically with addition of silicone oil. Although the solubilization of water in the reverse cubic phase is low, a very large amount of excess water can be incorporated in a so-called reverse cubic phase based concentrated emulsion. The emulsion stability is enhanced upon addition of silicone oil. D4 molecules penetrate into the surfactant palisade layer in the reverse micelles forming the I2 phase and expand the effective cross-sectional area per surfactant, aS (penetration). The continuous penetration of oil destabilizes the I2 phase structure, and therefore the melting temperature of the phase decreases. The incorporation of D4 into the I2 phase in the aqueous mixtures of Si14C3EO7.8, Si25C3EO7.8, Si25C3EO12.2, and Si25C3EO15.8 varies with both the hydrophilic and lipophilic chain lengths of silicone surfactants.