Nonionic phase behavior

For nonionic amphiphiles, the effects of temperature on the phase behavior are large and the effects of inorganic electrolytes are very small. However, for ionic surfactants temperature effects are usually small, but effects of inorganic electrolytes are large. Most common electrolytes (eg, NaCl)... 

The most frequent emulsiflcation using phase inversion is known as the PIT (Phase Inversion Temperature) method [81-83] and occurs through a temperature quench. This method is based on the phase behavior of nonionic surfactants and the correlation existing between the so-called surfactant spontaneous curvature and the type of emulsion obtained. 

H. Kunieda and K. Shinoda Phase Behavior in Systems of Nonionic Surfac-tant/Water/Oil Around the Hydrophilic-Lypophilic-Balance-Temperature. J. Dispersion Sci. Technol. 3, 233 (1982). 

Figure 7 indicates the phase behavior of SOW systems containing ternary nonionic surfactant mixtures that in turn contain a very hydrophilic surfactant (Tween 60 Sorbitan -i- 20 EO stearate), a very hpophihc surfactant (Span 20 Sorbitan monolaurate), and an intermediate (Tween 85 Sorbitan 20 EO trioleate or Nonylphenol with an average of 5 EO groups). The two intermediate surfactants correspond exactly to an optimum formulation in the physicochemical conditions, i.e., they exhibit three-phase behavior with the system 1 wt. % NaCl brine-heptane-2-butanol. As the intermediate hy-drophihcity surfactant is replaced by an equivalent mixture of the extreme ... 

This last case is a combination of the two previous ones, in which the pH has an opposite effect on two surfactants. As shown in Fig. 17 (upper part) and discussed in Sect. 5.2 an increase in pH increases the ionization of the fatty acid, i.e., the proportion of the ionized hydrophilic soap, and hence the hy-drophilicity of the acid-soap mixture in the water phase and consequently at the interface. At low pH, the acid, i.e., a lipophilic nonionic surfactant, prevails, whereas at high pH, it is the hydrophilic soap that dominates the formulation. The pH at which about half of the interfacial mixture is acid and half soap, i.e., the pH at which the interfacial mixture is at optimum formulation (and three-phase behavior is exhibited), is called pH in Fig. 17. 

This happens when the pH of the acid-soap system is lower than the pH of the amine-salt systems. This is the case of Fig. 17, if the two pH scales are assumed to be coincident. For some intermediate pH both systems exhibit a WI phase behavior, that is to say that they contain a high percentage of the corresponding ionized species. If both the acid and amine are placed in the same system at such a pH, the two ionic species would combine to produce a catanionic one, in equilibrium with the nonionic acid and amine species. Therefore, five surfactants would be present in the system, with relative proportions directly linked to the pH through the dissociation equilibria, the partitioning equilibria, and the catanionic association equilibriiun. How the phase behavior is altered by the pH through this complex scheme, does not seem easy to deduce and an experimental approach is surely the safer one. 

Bourrel M, Salager JL, Schechter RS, Wade WH (1980) A Correlation for Phase Behavior of Nonionic Surfactants. J Colloid Interface Sci 75 451-461... 

Anton RE, Salager JL, Graciaa A, Lachaise J (1992) Surfactant-oil-water systems near the affinity inversion - Part Vlll Optimum Formulation and phase behavior of mixed anionic-nonionic systems versus temperature. J Dispers Sci Technol 13 565... 

Mori F, Lim JC, Raney OG, Elsik CM, Miller CA (1989) Phase behavior, dynamic contact angle and detergency in systems containing triolene and nonionic siufactants. Colloid Surf 40 323-345... 

To single out the peculiarities in the phase behavior of ionic fluids, it is convenient to consider first the behavior of nonionic (e.g., van der Waals-like) mixtures. We note, however, that the subsequent considerations ignore liquid-solid phase equilibria, which in real electrolyte solutions can lead to far more complex topologies of the phase diagrams than discussed here [150],... 

This article discusses some micellar and liquid crystalline phases with nonionic substances, water, and hydrocarbons and some factors are delineated for their association phenomena. Lipid phase behavior has an extremely important direct influence on certain biological phenomena (Chapter 10) and is treated in Chapter 4. The treatment here is limited... 

The preliminary results reported here indicate that the general changes induced in the PIT range may help to systematize the complex phase behavior of nonionic surfactants when they are combined with water and hydrocarbons. 

Nonionic surfactants tend to show the opposite temperature effect As the temperature is raised, a point may be reached at which large aggregates precipitate out into a distinct phase. The temperature at which this happens is referred to as the cloud point. It is usually less sharp than the Krafft temperature.2 The phenomenon that nonionic surfactants become less soluble at elevated temperature will be important when we discuss the phase behavior of emulsions. 

M. Kahlweit and R. Strey. Phase-behavior of ternary-systems of the type H20-oil-nonionic amphiphile (microemulsions). Angewandte Chemie. International edition in English, 24(8) 654—668,1985. 

Previous work has shown that binary surfactant systems containing Dowfax 8390 and the branched hydrophobic surfactant AOT can form Winsor III systems with both PCE and decane whereas DOWFAX 8390 by itself cannot (Wu et. al. 1999). This binary surfactant system was used in conjunction with hydrophobic octanoic acid to help with phase behavior and lessen the required concentration of CaCl2. Since this formulation is rather complicated, questions about field robustness arise. Thus, for the phase behavior studies presented here, we used the simple binary system of the nonionic TWEEN 80 and the branched hydrophobic AOT, and we optimized the NaCl concentration to give the Winsor Type III system. The lesser electrolyte concentration requirement for the binary TWEEN 80/ AOT system helps to decrease the potential for undesirable phase behavior such as surfactant precipitation, thereby increasing surfactant system robustness. 

A limited number of studies have considered the use of surfactant and cosolvent mixtures to enhance the recovery of NAPLs (Martel et al., 1993 Martel and Gelinas, 1996). Martel et al. (1993) and Martel and Gelinas (1996) employed ternary phase diagrams to select surfactant+cosolvent formulatons for treatment of NAPL-contaminated aquifers. The surfactant+cosolvent formulations used in their work, which included lauryl alcohol ethersulfate/n-amyl alcohol, secondary alkane sulfonate/n-butanol, and alkyl benzene sulfonate/n-butanol, were shown to be effective solubilizers of residual trichloroethene (TCE) and PCE in soil columns (Martel et al., 1993). However, very little information is available regarding the effect of cosolvents on the solubilization capacity and phase behavior of ethoxylated nonionic surfactants. 

Time - resolved spectra of a solid hydrocarbon layer on the surface of an internal reflection element, interacting with an aqueous solution of a nonionic surfactant, can be used to monitor the detergency process. Changes in the intensity and frequency of the CH2 stretching bands, and the appearance of defect bands due to gauche conformers indicate penetration of surfactant into the hydrocaibon layer. Perturbation of the hydrocarbon crystal structure, followed by displacement of solid hydrocaibon from the IRE surface, are important aspects of solid soil removal. Surfactant bath temperature influences detergency through its effects on both the phase behavior of the surfactant solution and its penetration rate into the hydrocaibon layer. 

Solid soils are commonly encountered in hard surface cleaning and continue to become more important in home laundry conditions as wash temperatures decrease. The detergency process is complicated in the case of solid oily soils by the nature of the interfacial interactions of the surfactant solution and the solid soil. An initial soil softening or "liquefaction", due to penetration of surfactant and water molecules was proposed, based on gravimetric data (4). In our initial reports of the application of FT-IR to the study of solid soil detergency, we also found evidence of rapid surfactant penetration, which was correlated with successful detergency (5). In this chapter, we examine the detergency performance of several nonionic surfactants as a function of temperature and type of hydrocarbon "model soil". Performance characteristics are related to the interfacial phase behavior of the ternary surfactant -hydrocarbon - water system. 

Similar attempts were made by Likhtman et al. [13] and Reiss [14]. Reference 13 employed the ideal mixture expression for the entropy and Ref. 14 an expression derived previously by Reiss in his nucleation theory These authors added the interfacial free energy contribution to the entropic contribution. However, the free energy expressions of Refs. 13 and 14 do not provide a radius for which the free energy is minimum. An improved thermodynamic treatment was developed by Ruckenstein [15,16] and Overbeek [17] that included the chemical potentials in the expression of the free energy, since those potentials depend on the distribution of the surfactant and cosurfactant among the continuous, dispersed, and interfacial regions of the microemulsion. Ruckenstein and Krishnan [18] could explain, on the basis of the treatment in Refs. 15 and 16, the phase behavior of a three-component oil-water-nonionic surfactant system reported by Shinoda and Saito [19],... 

Shinoda and Kuineda [8] highlighted the effect of temperature on the phase behavior of systems formulated with two surfactants and introduced the concept of the phase inversion temperature (PIT) or the so-called HLB temperature. They described the recommended formulation conditions to produce MEs with surfactant concentration of about 5-10% w/w being (a) the optimum HLB or PIT of a surfactant (b) the optimum mixing ratio of surfactants, that is, the HLB or PIT of the mixture and (c) the optimum temperature for a given nonionic surfactant. They concluded that (a) the closer the HLBs of the two surfactants, the larger the cosolubilization of the two immiscible phases (b) the larger the size of the solubilizer, the more efficient the solubilisation process and (c) mixtures of ionic and nonionic surfactants are more resistant to temperature changes than nonionic surfactants alone. 

The effect of the oily component on the phase behavior of o/w ME-forming systems formulated with nonionic surfactants was reported [23].The authors showed that it is possible to formulate cosurfactant-free o/w ME systems suitable for use as drug delivery vehicles using either polyoxyethylene surfactants or amine-A-oxide surfactants. The major advantage of these ME systems is their ability to be diluted without destroying their integrity however both classes of surfactants were shown to be sensitive to electrolytes. 

Samii, A. A. Lindman, B. Karstrom, G., "Phase Behavior of Some Nonionic Polymers in Nonaqueous Solvents," Prog. Coll. Polym. Sci., 82, 280 (1990). 

In this article we describe the phase behavior of a microemulsion system chosen for the free radical polymerization of acrylamide within near-critical and supercritical alkane continuous phases. The effects of pressure, temperature, and composition on the phase behavior all influence the choice of operating parameters for the polymerization. These results not only provide a basis for subsequent polymerization studies, but also provide data on the properties of reverse micelles formed in supercritical fluids from nonionic surfactants. 

---