Foams From A Three-phase Emulsion

Foam stability was related to phase behavior in a foamed three-phase region consisting of an aqueous solution (L1), an alcohol solution (L2) and lamellar liquid-crystalline (LC) phases in the C8H17SO3Na/C8H17OH/H2O system. The state of the system before foaming was LC/L2 + LC/L1 or L1 + L2/LC type emulsions up to a high octanol/water ratio of 77/23. In L2 + LC/L1 emulsion, the LC droplets exist separately from the alcohol droplets in an aqueous continuous medium. The viscosity of the system was enhanced with an increase in the content of dispersed phases, i.e. alcohol and/or liquid crystal phases contributing to the stabilizing of the foam. With higher than optimal liquid-crystalline phases present the high viscosity prevented foaming. Higher than optimal alcohol amounts led to phase inversion and instability. The drainage rate of the alcohol phase was considerably faster than of the other phases. As a result, the three-phase foam was stabilized by the liquid-crystalline phase for the water continuous part of the system in spite of the presence of a foam-destabilizing compound, octanol. © 1986

Stability Of Hydrophobic Foams

The stability of foams was determined in two-phase regions containing an isotropic hydrocarbon solution and a lamellar liquid crystal. The lamellar liquid crystal showed surface activity with regard to the hydrocarbon solution. This was interpreted as due to the higher frequency of methyl groups at the surface of the liquid-crystalline state compared to the liquid state. The weaker intermolecular forces from the methyl groups were assumed to result in a lower surface tension of the liquid crystal in comparison to the liquid. This hypothesis was tested by the use of a low surface tension hydrocarbon, isooctane. No foam stability was formed in this medium, supporting the claim of the methyl groups as the surface-active element. © 1986, American Chemical Society. All rights reserved

ESR study on the stability of W/O gel-emulsions

W/O gel-emulsions (high-internal-phase-volume-ratio emulsions) form in water (or brine) /tetraethyleneglycol dodecyl ether/heptane system above the HLB (hydrophile-lipophile balance) temperature of the system. A salt, which largely decreases cloud temperature in a water-nonionic surfactant system, makes the surfactant film rigid and the gel-emulsions hence become very stable. The effect of aded salt on the apparent order parameter "S", and the isotropic hyperfine splitting constant "aN" in gel-emulsions was determined by the ESR spin probe method using 5-doxyl stearic acid as the spin probe. The apparent order parameter "S", and the isotropic hyperfine splitting constant "aN" increase with increasing salinity in Na2SO4, CaCl2, and NaCl systems. It is considered that the surfactant molecules are tightly packed in these systems and this tendency is highly related to the stability of gel-emulsions. The salt dehydrates the hydrophilic moiety of surfactant and hence the lateral interactions of surfactant molecular layer at the water-oil interface increases. The observed difference in the apparent order parameter between the ordinary emulsions and the gel-emulsions suggests that most of the surfactant molecules are adsorbed at the oil-water interface (the surface of the water droplet) in gel-emulsions.Peer reviewe

Spontaneous formation of highly concentrated oil-in-water emulsions

Highly concentrated oil-in-water-type emulsions are spontaneously formed by a rapid decrease in temperature in the 0.1 M NaCl aqueous solution/hexaethylene glycol dodecyl ether/monolaurin/n-decane system. The change in the self-organizing structures was monitored by electric conductivity and the results were interpreted on the basis of phase behavior. The spontaneous curvature of the surfactant molecular layer changes from concave to convex toward water with decreasing temperature. The reason is that surfactant self-organizing structures change from a water-in-oil microemulsion to a highly concentrated emulsion via lamellar liquid crystal and reverse bicontinuous (reverse L3) phases. It is important to lower the temperature quickly to form stable highly concentrated emulsions with fine droplets, because the system passes through an extremely unstable emulsion region.Peer reviewe

The stability of gel-emulsions in a water/nonionic surfactant/oil system

Viscous and translucent gels form in a very diluted region (water-rich region) in water/nonionic surfactant/oil systems. The effects of salt and other additives on the stability of these W/O-type gels have been studied. The gels were stabilized dramatically by added salt. Their stable region was apparently widened in the phase diagram, but salt does not improve the transparency of the gels. Salts which have a large salting-out effect, decreasing the cloud temperature in a water/ nonionic surfactant system, are more effective in stabilizing the gels. It is considered that the lateral interaction of surfactant molecules increases in the presence of salt. Although gels are not formed in an aromatic hydrocarbon system using a poly(ethylene glycol)-type surfactant, they are produced by using monolaurin as surfactant. The stability of the gels is dramatically enhanced by adding lecithin. These observations suggest that increasing the lateral interaction of surfactant molecules stabilizes the gels. However, if the lateral interactions between surfactant molecules become too strong, as in a system including a lamellar liquid crystalline phase, then gels do not form. The gels consist of two isotropic liquid phases in all of our systems. © 1989.Peer reviewe