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

The phase behavior of long hydrophobic A−B type silicone surfactants, Me 3 SiO−(Me 2 SiO) m - 2 −Me 2 SiCH 2 CH 2 CH 2 −O−(CH 2 CH 2 O) n H (Si m C 3 EO n ), in water and water + octamethylcyclotetrasiloxane (D 4 ) was investigated by studying phase behavior and small-angle X-ray scattering. Si 25 C 3 EO 15.8 forms a reverse micellar cubic phase (I 2 ) in water and water + D 4 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. D 4 molecules penetrate into the surfactant palisade layer in the reverse micelles forming the I 2 phase and expand the effective cross-sectional area per surfactant, a S (penetration). The continuous penetration of oil destabilizes the I 2 phase structure, and therefore the melting temperature of the phase decreases. The incorporation of D 4 into the I 2 phase in the aqueous mixtures of Si 14 C 3 EO 7.8, Si 25 C 3 EO 7.8, Si 25 C 3 EO 12.2, and Si 25 C 3 EO 15.8 varies with both the hydrophilic and lipophilic chain lengths of silicone surfactants.