Binary surfactant-water systems

As in binary surfactant-water systems considered previously, two constraints on the geometry of the surfactant interface are active a local constraint, which is due to the surfactant molecular architecture, and a global constraint, set by the composition. These constraints alone are sufficient to determine the microstructure of the microemulsion. They imply that the expected microstructure must vary continuously as a function of the composition of tile microemulsion. Calculations show - and small-angle X-ray and neutron scattering studies confirm - that the DDAB/water/alkane microemulsions consist of a complex network of water tubes within the hydrocarbon matrix. As water is added to the mixture, the Gaussian curvature - and topology -decreases [41]. Thus the connectivity of the water networks drops (Fig. 4.20). 

At higher surfactant concentration liquid crystalline phases may be formed. Surfactant liquid crystals can also solubilise appreciable amounts of oil into the non-polar regions made up of the surfactant tails. Thus, both binary surfactant-water systems and ternary systems with oil included can be formulated into liquid crystals. Such systems can also be used as media for organic synthesis. In fact, a reaction in a surfactant liquid crystal often runs very rapidly, considerably faster than in a microemulsion based on the same surfactant [19]. Figure 5.1 shows the reaction profiles of a typical substitution reaction of... 

Figure 17 Idealized, theoretical phase diagram for a binary surfactant/water system (Li is a solution of micelles, L2 is a solution of reversed micelles).

Liihmann and Finkelmann also reported what was the first nematic phase observed in a binary nonionic/water system [ 132]. It was formed by the surfactant H2C=CH-CH2-0-0-0-0-CH2-COO(CH2CH20)7CH3. 

This chapter will focus on a simpler version of such a spatially coarse-grained model applied to micellization in binary (surfactant-solvent) systems and to phase behavior in three-component solutions containing an oil phase. The use of simulations for studying solubilization and phase separation in surfactant-oil-water systems is relatively recent, and only limited results are available in the literature. We consider a few major studies from among those available. Although the bulk of this chapter focuses on lattice Monte Carlo (MC) simulations, we begin with some observations based on molecular dynamics (MD) simulations of micellization. In the case of MC simulations, studies of both micellization and microemulsion phase behavior are presented. (Readers unfamiliar with details of Monte Carlo and molecular dynamics methods may consult standard references such as Refs. 5-8 for background.)... 

Liihmann and Finkelmann also made the first published report of a nematic phase in a binary nonionic/water system (148). This was formed by discshaped micelles of the surfactant H2C=CH-CH2-O-0-0-O-CH2-COO(CH2CH2O)7CH3, being observed between the Li and phases in a narrow band of 34-38% surfactant between 7.5 and 23.4°C (Figure 21.24). The phase exists up to 72% surfactant (and to 80% in a bi-phasic region with water). Clouding is seen over a wide concentration range (up to > 90% surfactant) with a lower critical temperature of 33.2°C. 

A phenomenon closely related to the formation of micelles is the building up of thermodynamically stable emulsions, so-called microemulsions. The process giving rise to the final formation of a microemulsion is the so-called solubilization, i.e. the encaging of the respective antagonistic component in the binary oil/water system by the surfactant. It might appear reasonable to consider... 

The presence of nonfreezable water was demonstrated, e.g., in binary ionic surfactant-water systems with surfactants such as AOT [151], sodium dioctyl-phosphinate [152], didodecyldimethylammonium bromide [44,45], and dioctade-cyldimethylammonium bromide [44]. 

Furthermore, the behavior of the two relevant unary systems (surfactant and water) must be known before the physical science of binary systems can be fully understood [17], C12MG was studied in depth following these principles, so we begin with a description of the equilibrium and kinetic aspects of the phase behavior of the unary (dry) C12MG system. Then these same aspects of the binary C12MG water system will be considered. The binary phase diagram that resulted from these studies has been pubUshed [18]. 

Only a limited number of studies of cationic surfactant-water systems have been reported. Fig. 2.6 shows the phase behaviour for the binary system dodecyltrimethylammonium chloride-water [23]. The interesting feature of this binary System is the appearance of two distinct cubic mesomorphic phases. An extensive range of techniques including optical microscopy, differential thermal analysis, proton magnetic resonance and low-angle X-ray diffraction were used to... 

In these lectures we present synchrotron x-ray scattering data for two lipidic and three surfactant systems in their multilayered phases. In the first surfactant system the neutral membrane consists of water layers coated with a mixture of the surfactant sodium-dodecyl-sulfate (SDS) and the cosurfactant (pentanol). The layers are separated by dodecane (i.e. an oil dilution study). In the second and third surfactant systems, the negatively charged membranes consist of a mixture of SDS and pentanol, while the solvent separating the membranes is either pure water or brine ( 0.5 mole of NaCl). The lipidic systems consists of a ternary mixture of di-myristoyl-phosphotidyl-choline (DMPC), water, and the cosurfactant pentanol,5 and the binary DMPC-water system. 27... 

An example for a partially known ternary phase diagram is the sodium octane 1 -sulfonate/ 1-decanol/water system [61]. Figure 34 shows the isotropic areas L, and L2 for the water-rich surfactant phase with solubilized alcohol and for the solvent-rich surfactant phase with solubilized water, respectively. Furthermore, the lamellar neat phase D and the anisotropic hexagonal middle phase E are indicated (for systematics, cf. Ref. 62). For the quaternary sodium octane 1-sulfonate (A)/l-butanol (B)/n-tetradecane (0)/water (W) system, the tricritical point which characterizes the transition of three coexisting phases into one liquid phase is at 40.1°C A, 0.042 (mass parts) B, 0.958 (A + B = 56 wt %) O, 0.54 W, 0.46 [63]. For both the binary phase equilibrium dodecane... 

There is a common rule, called Bancroft s rule, that is well known to people doing practical work with emulsions if they want to prepare an O/W emulsion they have to choose a hydrophilic emulsifier which is preferably soluble in water. If a W/O emulsion is to be produced, a more hydrophobic emulsifier predominantly soluble in oil has to be selected. This means that the emulsifier has to be soluble to a higher extent in the continuous phase. This rule often holds but there are restrictions and limitations since the solubilities in the ternary system may differ from the binary system surfactant/oil or surfactant/water. Further determining variables on the emulsion type are the ratios of the two phases, the electrolyte concentration or the temperature. 

A single relaxation was observed for the binary water-surfactant system and the results obtained are in good agreement with those previously reported [8]. A relatively weak sound absorption (ca. 1-4 MHz) is apparent in alcohol-water systems for the more concentrated solutions of Bu and Pe. 

Furfiier evidence fiiat supports these calculations derives from studies of the ternary mixtures of the cationic double-chain surfactant DDAB (didodecyl dimethyl ammonium bromide), cyclohexane and water. Within the cubic mesophase region of fiiis surfactant-water-oil mixtiure, all the cyclohexane is adsorbed between the surfactant chains, so that the system is a pseudo-binary one, for which our theoretical analysis ought to hold. (The effective surfactant parameter for fliis surfactant in the presence of cyclohexane is slightly larger tiian unity.) Close scrutiny of the cubic phase region within this ternary phase diagram has revealed the presence of at least one - and... 

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