Degradation of kinetically-stable o/w emulsions.

Amphiphile lyotropic liquid crystalline self-assembly materials are being used for a diverse range of applications. Historically, the most studied lyotropic liquid crystalline phase is probably the one-dimensional (1-D) lamellar phase, which has been employed as a model system for biomembranes and for drug delivery applications. In recent years, the structurally more complex 2-D and 3-D ordered lyotropic liquid crystalline phases, of which reversed hexagonal (H2) and reversed cubic phases (v2) are two prominent examples, have received growing interest. As is the case for the lamellar phase, these phases are frequently stable in excess water, which facilitates the preparation of nanoparticle dispersions and makes them suitable candidates for the encapsulation and controlled release of drugs. Integral membrane protein crystallization media and templates for the synthesis of inorganic nanostructured materials are other applications for 2-D and 3-D amphiphile self-assembly materials. The number of amphiphiles identified as forming nanostructured reversed phases stable in excess solvent is rapidly growing. In this article, different classes of amphiphiles that form reversed phases in excess solvent are reviewed, with an emphasis on linking phase behavior to amphiphile structure. The different amphiphile classes include: ethylene oxide-, monoacylglycerol-, glycolipid-, phosphatidylethanolamine-, and urea-based amphiphiles.

Ordered 2-D and 3-D nanostructured amphiphile self-assembly materials stable in excess solvent

The formation of mesoporous silica materials has been studied using blends of diblock (CnH2n+1(OCH2CH2)xOH, CnEOx, n = 12 − 18 and x = 2−100) and Pluronic triblock (EOxPO70EOx, x = 5−100) amphiphilic block copolymers as the structure-directing agents and sodium silicate as the silica source. The mesostructure of the silica materials thus obtained, as determined by X-ray diffraction and transmission electron microscopy, changes as the volume of the hydrophilic EO group of the surfactant increases, from lamellar to two-dimensional hexagonal (p6mm), three-dimensional hexagonal, a cubic phase, and another cubic phase with Im3m symmetry. Particle morphologies of the mesoporous silica materials are correspondingly changed from sheetlike to irregular, facetted cubic shapes depending on the periodic mesoscale symmetry of the structure. It is reasonable that the structural transformations are due to the changes in hydrophobic surface curvatures, which can be controlled readily and precisely by using polymer blend...

Structural Design of Mesoporous Silica by Micelle-Packing Control Using Blends of Amphiphilic Block Copolymers

Complex Fluids of Poly(oxyethylene) Monoalkyl Ether Nonionic Surfactants

The effect of added decane, m-xylene, or squalane on the phase behavior of the polyoxyethylene dodecyl ether (C12EOn) −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, aS. 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 aS is almost co...

Effect of Oil on the Surfactant Molecular Curvatures in Liquid Crystals

A phase diagram of a water−poly(oxyethylene) oleyl ether (POlE) system was constructed as a function of poly(oxyethylene) chain length at 25 °C. The POlEs contain a highly pure oleyl group, whose purity is above 99.7%. The POlEs are in a liquid state over a wide range of composition. The increase in the poly(oxyethylene) (EO) chain of POlE corresponds to the increase in the curvature of surfactant layer toward water or the increase in HLB (hydrophile−lipophile balance) number of the surfactant. Various self-organizing structures were found:  hexagonal and lamellar lquid crystals, four kinds of isotropic liquid crystals, a sponge phase, and reverse hexagonal liquid crystal. The phase transition between normal hexagonal and lamellar liquid crystals were investigated at constant volume fraction of the oleyl group in system by means of small-angle X-ray scattering. Correlation among the phase behavior, the packing of oleyl chain in self-organizing structures, and the HLB of POlE is discussed. The effect of te...

Self-Organizing Structures in Poly(oxyethylene) Oleyl Ether−Water System

Phase behavior, micellar structure, and cloud point have been investigated in water/long poly(oxyethylene)n oleyl ether (C18:1EOn) (n = 10.7, 19.2, 30.1, and 50.8) systems. With increasing n, the discontinuous micellar cubic phase (I1) becomes increasingly stable, effectively replacing hexagonal and lamellar liquid crystalline phases. From NMR self-diffusion measurements in the liquid micellar phase at lower concentrations, we found that micelles at larger n remain spherical and interact to a good approximation as hard spheres up to crystallization. In the cubic phase, small-angle X-ray data indicate a body-centered cubic arrangement. The aggregation number of the micelles monotonically decreases with increasing EO chain length, but the micellar molecular weight first decreases and then turns to increase at a certain EO chain length because of the increase of molecular weight of the surfactant molecule. As a result, the cloud point first increases with increasing EO chain length, reaches a maximum, and th...

Correlation between Micellar Structure and Cloud Point in Long Poly(oxyethylene)n Oleyl Ether Systems

Phase behavior of mixed polyoxyethylene-type nonionic surfactants in water

Cubic-Phase-Based Concentrated Emulsions.

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 (C12EO4.8) containing C12EO8+C12EO3, a single I1 phase region is not present in a pseudo ternary phase diagram of water/C12EO4.8/decane system, but an I1+O region appears in the oil-rich region. C12EO4.8 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.

Kazuki Shigeta

Papers

Self-Organizing Structures in Poly(oxyethylene) Oleyl Ether−Water System

Correlation between Micellar Structure and Cloud Point in Long Poly(oxyethylene)n Oleyl Ether Systems

Phase behavior of mixed polyoxyethylene-type nonionic surfactants in water

Cubic-Phase-Based Concentrated Emulsions.

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