Surfactant equilibrium phase diagram

Prinsen et al. [23] and Warren et al. [31] used dissipative particle dynamics to simulate dissolution of a pure surfactant in a solvent. Tuning surfactant-surfactant, surfactant-solvent, and solvent-solvent interactions to yield an equilibrium phase diagram similar to Fig. 1 at low temperatures except for the absence of the V i phase, they found that the kinetics of formation of the liquid crystalline phases at the interfaces was rapid and that the rate of dissolution was controlled by diffusion, in agreement with the above experimental results. 

Phase Behaviour. The differences in the self-emulsifying behaviour of Tagat TO - Miglyol 812 binary mixtures can, in part, be explained from considerations of their phase behaviour. Figures 4a-4d show the representative equilibrium phase diagrams obtained when binary mixtures containing 10,25,30 and 40J surfactant were sequentially diluted with water. The phase notation used is based on that of Mitchell et ai (li). 

The production of corrosion-resistant materials hy alloying is well established, hut the mechanisms are noi lull) understood. It is known, of course, that elements like chromium, mckcl. titanium, and aluminum depend for their corrosion resistance upon a tenacious surface oxide layer (passive film). Alloying elements added for the purpose of passivation must be in solid solution. The potential of ion implantation is promising because restrictions deriving from equilibrium phase diagrams frequently do not applv li e., concentrations of elements beyond tile limits of equilibrium solid solubility might he incorporated). This can lead to heretofore unknown alloyed surfact-s which are very corrosion resistant... 

The interfacial tension y at the planar interface has a minimum near the temperature Indeed, at the latter temperature r is small, A/jt0 = 0 and because d ij w/d J and dfi /dT have opposite signs and s is also small (because T is small), dy/d I 0. The temperature T0 is provided by Eq. (25) and is independent of the concentration of surfactant. In other words, the two minima of Fig. 4 which correspond to the phase inversion temperatures of a macroemulsion (the curve with a positive minimum) and microemulsion (the curve with a negative minimum) are the same. When emulsions are generated from a microemulsion and its excess phase, the emulsion is of the same kind as the microemulsion, the phase inversion temperature is obviously located in the middle of the middle phase microemulsion range and the above conclusion remains valid. The above results explain the observation of Shinoda and Saito [6,7] that the phase inversion temperature (PIT) of emulsions can be provided by the ternary equilibrium phase diagram. 

Using one of the pure alkyl aryl sulfonates with water, sodium chloride and decane, we are investigating simultaneously the phase behavior, the structure of the phases, and the interfacial tensions between them. Ultralow tensions are observed in this system (10), and it is important to know why they occur, when they do (13). Our first aim is to establish the equilibrium phase diagram of surfactant-water-decane as a function of... 

Figure 15.2 shows typical binary (surfactant + water) phase diagrams of monoglycerides for three molecules with decreasing Krafft temperature (l-monopahnitin, 1-mono-elaidin and 1-mono-olein). With 1-monopalmitin, the dominant meso-phase is the lamellar (neat) phase, which swells to a maximum water layer thickness, dw, of 2.1 nm at 40% water. At higher water content (>60%) a disperse phase is produced in the temperature range 55-68 °C, whereas above 68 °C a cubic phase in equilibrium with water is formed. 

In summary, the above studies provide the equilibrium phase diagram of the Ci2MG-water system below 80°C. This work established, in addition, that the cloud point boundary is absent below 100 °C. (This is the boundary of the liquid/liquid miscibility gap commonly found in the diagrams of nonionic surfactant water systems). The absence of the cloud point boundary is significant with respect to analysis of the intrinsic hydrophilicity of this poly functional group [2]. The kinetic and nonequilibrium aspects of the phase behavior of aqueous C12MG mixtures will now be considered. 

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... 

If we assume that the data of Figs. 22 and 23 can be treated by equilibrium thermodynamics, the discontinuities in the ESP versus temperature phase diagram should indicate the presence of a three-way equilibrium between bulk surfactant and two different film types in both homo- and hetero-chiral systems. The surface heats of transition (U) between the two film types in either system may be obtained by relation (15), where IT is the equilibrium... 

Figure 1.4. For a nonionic surfactant, influence of the temperature on (a) the surfactant morphology and hence the spontaneous curvature, (b) the type of self-assembly, (c) the phase diagram, the number of coexisting phases is indicated (d) the coexisting phases at equilibrium, and (e) the corresponding emulsions.

Winsor reported that the phase behavior of SOW systems at equilibrium could exhibit essentially three types, so called Wl, Wll and Will, illustrated by the phase diagrams indicated in Fig. 1. In the Wl (respectively, Wll) case, the surfactant bears a stronger affinity for the water (respectively, oil) phase and most of it partitions into water (respectively, oil). As a consequence, the system exhibits a two-phase behavior in which a microemulsion is in equihb-rium with excess oil (respectively, water). 

Peters and Luthy (1993, 1994) performed a detailed analysis of the equilibrium behavior of solvent coal tar water mixtures in work that was complementary to column studies performed by Roy, et. al. (1995). Peters and Luthy successfully modeled ternary phase diagrams of coal tar/n-butylamine/water systems. In addition, Peters and Luthy identified n-butylamine as the leading solvent for coal tar extraction. Pennell and Abriola (1993) report the solubilization of residual dodecane in Ottawa sand using a nonionic surfactant, polyoxyethylene sorbitan monooleate, which achieved a 5 order of magnitude increase over the aqueous solubility, but is still 7 times less than the equilibrium batch solubility with the same surfactant system. 

The phase diagrams of aqueous surfactant systems provide information on the physical science of these systems which is both useful industrially and interesting academically (1). Phase information is thermodynamic in nature. It describes the range of system variables (composition, temperature, and pressure) wherein smooth variations occur in the thermodynamic density variables (enthalpy, free energy, etc.), for macroscopic systems at equilibrium. The boundaries in phase diagrams signify the loci of system variables where discontinuities in these thermodynamic variables exist (2). 

The presence of mixed surfactant adsorption seems to be a factor in obtaining films with very viscous surfaces [411]. For example, in some cases the addition of a small amount of non-ionic surfactant to a solution of anionic surfactant can enhance foam stability due to the formation of a viscous surface layer, which is possibly a liquid crystalline surface phase in equilibrium with a bulk isotropic solution phase [25,110], In general, some very stable foams can be formed from systems in which a liquid crystal phase is present at lamella surfaces and in equilibrium with an isotropic interior liquid. If only the liquid crystal phase is present, stable foams are not produced. In this connection foam phase diagrams may be used to delineate compositions that will produce stable foams [25,110],... 

The maximum additive concentration (MAC) is defined as the maximum amount of solubilisate, at a given concentration of surfactant, that produces a clear solution. Different amounts of solubilisates, in ascending order, are added to a series of vials containing the known concentration of surfactant and mixed until equilibrium is reached. The maximum concentration of solubilisate that forms a clear solution is then determined visually. This same procedure can be repeated for the different concentrations of surfactant in a known amount of solubilisate in order to determine the optimum concentration of surfactant (Figure 4.24). Based on this information, one can construct a ternary phase diagram that describes the effects of three constituents (i.e., solubilisate, surfactant, and water) on the micelle system. Note that unwanted phase transitions can be avoided by ignoring the formulation compositions near the boundary. In general, the MAC increases with an increase in temperature. This may be due to the combination of the increase of solubilisate solubility in the aqueous phase and the micellar phase rather than an increased solubilization by the micelles alone. 

Preparation of Samples for Phase Diagrams. Stock solutions of appropriate concentrations of the A-B-A block copolymer In tetradecane and butan-l-ol were made up. All sanq>les were prepared by weight In glass, screw capped vials and In all cases mixing was carried out using a laboratory "Whlrllmlxer". The order of mixing the components was as follows, surfactant In tetradecane, tetradecane, butan-l-ol and finally water. All samples were sealed and kept at 23°C for one month to reach equilibrium. The samples were then studied, as described below, mixed resealed and kept at 47°C for a further month. The samples were then studied and then the procedure... 

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