Effect of Oil on the Surfactant Molecular Curvatures in Liquid Crystals

Abstract

The effect of added decane, m-xylene, or squalane on the phase behavior of the polyoxyethylene dodecyl ether (C12EO n ) −water system was investigated as a function of polyoxyethylene (EO) chain length at 25 °C. When the surfactant is relatively lipophilic (more lipophilic than the balanced state), the type of liquid crystal is changed to the more lipophilic one upon addition of decane. The lamellar (Lα) to lipophilic reverse hexagonal (H2) transition takes place in the C12EO3 system. On the other hand, the hexagonal (H1) to hydrophilic discrete cubic (I1) liquid crystal transition occurs in the hydrophilic C12EO7 system. There are two kinds of effects of oil on the self-organizing structures. One is the “penetration effect”, in which oil molecules penetrate into the surfactant palisade layer and expand the effective cross-sectional area, a S. The other is “swelling effect”, in which oil molecules are solubilized in the core of aggregates and expand the volume of aggregates. In this case, the a S is almost constant. Due to the swelling effect, the H1−I1 phase transition takes place in the decane−C12EO7 system, whereas the Lα−H2 transition occurs in the decane−lipophilic C12EO3 system due to the penetration effect. This causes the opposite tendency of the change in the curvature of the surfactant layers in liquid crystals on each side of the balanced state. As a result, the phase behavior of surfactant is quickly changed from forming micelles to reverse micelles within a narrow range of the EO chain in the presence of oil. On the other hand, m-xylene tends to penetrate the surfactant palisade layer, and the H1−Lα transition occurs even in the hydrophilic C12EO7 system.

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.…”

“…On the other hand if the oil molecules penetrate into a surfactant palisade layer, a positive curvature becomes less positive or even it is turned into a negative curvature (1). Note that a positive and a negative curvature of surfactant layer indicate a surfactant layer that is convex toward water and oil, respectively.…”

“…Note that a positive and a negative curvature of surfactant layer indicate a surfactant layer that is convex toward water and oil, respectively. The curvature of normal-type micelle or hexagonal phase tends to be less positive by the solubilization of oils with penetration tendency and to be more positive by the solubilization of oils with less-penetration tendency (1,11). Hence the phase transition from a micellar phase or a hexagonal phase to a discontinuous cubic phase takes place in the case of adding oils having less penetration tendency (13).…”

“…Hence the phase transition from a micellar phase or a hexagonal phase to a discontinuous cubic phase takes place in the case of adding oils having less penetration tendency (13). In previous reports (1,11), hydrocarbons or aromatic oils are mainly used to discuss the relation between the solubilization site of oils and the structural change of self-assemblies. However there are few reports for triglyceride oils in spite of the importance of practical applications.…”

Caracterización de cristales líquidos por microscopía óptica en sistemas surfactante polietoxilado-alcano-agua

“…[16][17][18][19] Como se esperaba, el sistema con mayor extensión de la región inmiscible o fases bicontinuas, correspondió al dodecano (de menor solubilidad y afinidad en agua). Este resultado coincide con los descritos en la literatura [20][21][22] donde con los hidrocarburos de menor tamaño la interacción que promueve la miscibilidad del tensioactivo con las fases oleica y acuosa es menor comparada con las interacciones laterales entre las moléculas del tensioactivo, por ello la fase de cristal líquido tiende a formarse a concentraciones menores del surfactante.…”