Effect of Mixing Oils on the Hexagonal Liquid Crystalline Structures

Abstract

Structural change in hexagonal liquid crystal (H1) in the water/heptaoxyethylene dodecyl ether (C12EO7) system upon addition of mixed oil (m-xylene + decane) is investigated by phase study and small-angle X-ray scattering (SAXS). The surfactant layer curvature tends to be less positive or negative upon addition of the mixed oil at a high m-xylene/decane ratio, and the H1−Lα (lamellar liquid crystal) transition takes place. At a low m-xylene/decane ratio, however, the H1−I1 transition occurs with increasing mixed oil content, where I1 is a discontinuous micellar cubic phase. An excess oil phase directly separates from the H1 phase at a moderate m-xylene/decane ratio. The change in the effective cross sectional area per surfactant, a S, as a function of oil content was also measured at each mixing fraction of oils by SAXS. m-Xylene molecules tend to penetrate the surfactant palisade layer and widen a S, whereas decane molecules tend to be solubilized in the deep core of surfactant hydrophobic moieties and the a S is not largely expanded. The a S does not jump at each transition of H1−I1 and H1−Lα. Considering the volume of polyoxyethylene chain (EO chain), the repulsion between the EO chains may increase upon addition of decane, whereas it would decrease upon addition of m-xylene. To balance the repulsion with the attraction due to the interfacial tension between water and the lipophilic part without the big change in a S, the phase transitions take place but the change in the surfactant layer curvature is opposite in both oil systems.

Effect of Addition and Molecular Size of Triglyceride Oils on Phase Behavior and Surfactant Self-Assemblies

“…Hence the spontaneous curvature of the surfactant layer in the hexagonal phase is high at relatively low surfactant concentration and low at high concentration. It is reported (1,13,17,18) that the surfactant layer curvature is changed to opposite direction by adding oil depending on the surfactant hydrophilicity or the spontaneous curvature of surfactant layer, in which the highly positive curvature is changed to more positive by the solubilization of oil but the less positive curvature decreases more or it is changed to a negative curvature. Therefore the H 1 -I 1 transition at low surfactant concentration and the H 1 -L a transition at high surfactant concentration are observed by adding TOG.…”

Influence of Surfactant Hydrophilicity on the Formation of Transparent O/I1-Type Emulsions

“…One can also notice that the phase diagrams in Fig. 4 resemble the oil concentrationtemperature diagrams of the water/C 12 EO 7 /decane system 24 or water/C 12 EO 25 /perfume system 25 since the increase in both temperature and glycerol concentration induce the dehydration of surfactant hydrophilic groups. Similar changes have been observed in the C 12 EO 9 system Fig.…”

Solubilization of decane into gemini surfactant with a modified Jeffamine backbone: Design of hierarchical porous silica

“…In a paper dealing with the effect of oil on the structure of liquid crystals in polyoxyethylene dodecylether-water systems, Kunieda et al. [30,31] reported that saturated hydrocarbons such as decane favor a swelling of the hexagonal structure core cylinders, whereas aromatic hydrocarbons such as m-xylene tend to penetrate the surfactant palisade layer. In addition, the solubilization of aromatics and aliphatic solubilizates in block copolymer micelles has been investigated in detail by Nagaraján et al [32][33][34].…”