Nonionic surfactant mixtures

Commercial nonionic surfactants are mixtures of multiple species with different degrees of ethoxylation and typically with some distribution in hy- 

A significant increase in fp and similar elongated drops and emulsification were seen as the cloud point of 37 °C was approached for Dow s commercial secondary alcohol ethoxylate Tergitol 15-S-7 (Fig. 5). Its hydrophobe consists of various double-chain species with the sum of the chain lengths ranging between 11 and 15, and its average EO number is 7.3. In some cases a conical projection developed on the elongated drop, and a jet was emitted, which broke up into small droplets (Eig. 6). 

Eurther videomicroscopy investigations were conducted for model systems consisting of binary mixtures of pure nonionic surfactants [10]. The results indicated that the common source of the intriguing phenomena described above is that the more hydrophilic species dissolve faster, causing the remaining drop to become enriched in the less hydrophihc species, which are less soluble and dissolve more slowly. Indeed, the drop can achieve compositions 

The mechanism of formation of jets such as that in Fig. 6 is not clear but apparently is associated with swelling of the La or L3 phase (the latter can also exist at very low surfactant concentrations, as shown in Fig. 1). The phenomenon resembles the tip streaming observed in drops of liquids subjected to shear or extensional flows with surfactants present [12,13]. In these cases shear stresses from the flow in the external phase cause the drop to elongate and form a jet with a conical shape similar to that seen in Fig. 6. No such external flow is present here, but perhaps flow inside the drop accompanying the swelling process produces a similar effect. 

One way to visualize the source of the behavior described in the preceding paragraphs in terms of Fig. 1 is to recognize that temperatures of the various phase boundaries for the drop decrease as it becomes less hydrophihc during dissolution, eventually falhng below the experimental temperature. The shift 

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The critical micellar concentrations of anionic/nonionic surfactant mixtures examined are low in a saline medium, so that, at the concentrations injected in practice, the chromatographic effects resulting from the respective adsorption of monomers are masked. Such surfactants propagate simultaneously in the medium in the form of mixed micelles. 

In the remainder of this article, discussion of surfactant dissolution mechanisms and rates proceeds from the simplest case of pure nonionic surfactants to nonionic surfactant mixtures, mixtures of nonionics with anionics, and finally to development of myehnic figures during dissolution, with emphasis on studies in one anionic surfactant/water system. Not considered here are studies of rates of transformation between individual phases or aggregate structures in surfactant systems, e.g., between micelles and vesicles. Reviews of these phenomena, which include some of the information summarized below, have been given elsewhere [7,15,29]. 

The explanation for this behavior is similar to that given in the preceding section for nonionic surfactant mixtures. Adding a hydrophihc anionic surfactant raises the temperature at the cloud point and other phase transitions above those for pure Ci2(EO)4. If the amount of anionic added exceeds only slightly that needed for complete solubility, the final stages of the dissolution process are slow because preferential dissolution of the anionic causes the remaining drop to rise above its cloud point and nucleate small droplets of surfactant-rich liquid. But if the amount added is sufficiently large, drop composition remains below the cloud point in spite of preferential dissolution, with the result that dissolution is fast as with pure nonionic surfactants below their cloud points. 

The deviations from the Szyszkowski-Langmuir adsorption theory have led to the proposal of a munber of models for the equihbrium adsorption of surfactants at the gas-Uquid interface. The aim of this paper is to critically analyze the theories and assess their applicabihty to the adsorption of both ionic and nonionic surfactants at the gas-hquid interface. The thermodynamic approach of Butler [14] and the Lucassen-Reynders dividing surface [15] will be used to describe the adsorption layer state and adsorption isotherm as a function of partial molecular area for adsorbed nonionic surfactants. The traditional approach with the Gibbs dividing surface and Gibbs adsorption isotherm, and the Gouy-Chapman electrical double layer electrostatics will be used to describe the adsorption of ionic surfactants and ionic-nonionic surfactant mixtures. The fimdamental modeling of the adsorption processes and the molecular interactions in the adsorption layers will be developed to predict the parameters of the proposed models and improve the adsorption models for ionic surfactants. Finally, experimental data for surface tension will be used to validate the proposed adsorption models. 

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 ... 

It is worth noting that the effect of temperature on ionic and polyethoxy-lated nonionic surfactants is just opposite. As temperature increases, the nonionics become more lipophilic whereas the ionics turn more hydrophilic. By mixing the two types of surfactants in a proper proportion, these effects could cancel each other out, and the mixture is said to be insensitive to temperature. This interesting feature of ionic-nonionic surfactant mixtures may be considered as a synergy, since it could be very important in practice. Analysis of this feature is not included here, because plenty of information may be found in the literature on applications of such mixtures to equihbrated and emulsified systems [10,71-74]. 

Koukounis C, Wade WH, Schecheter RS (1983) Phase Partitioning of anionic and nonionic Surfactant Mixtures. Soc Petrol Eng J 23 301-310... 

Anton RE, Mosquera F, Oduber M (1995) Anionic-nonionic surfactant mixture to attain emulsion insensitivity to temperature. Prog Colloid Polym Sci 98 85... 

Having shown that ionic/nonionic surfactant mixtures show negative deviations from ideality (when both components are hydrocarbon—based) and fluorocarbon/hydrocarbon—based surfactant mixtures show positive deviations from ideality, what would a ionic fluorocarbon/nonionic hydrocarbon surfactant pair be expected to do In one example of this case (57). the electrostatic stabi1ization forces overcome the hydrophobic group phobicity effects and negative deviation from ideality is observed. 

When an ionic/nonionic surfactant mixture adsorbs on a metal oxide surface, the admicelle exhibits negative deviation from ideality (74). This means that the adsorption level is higher than it would be if the admicelle were ideal, at a specific surfactant concentration below the CMC. Above the CMC, the adsorption level is dictated by the relative enhancement of micelle formation vs. admicelle formation. In this region, the level of adsorption can be viewed as the result of the competition between micelles and admicelles for surfactant. In analogy, the surface tension above the CMC can be viewed as competition between the monolayer and micelles for surfactant. 

If the mixed micelle model already presented is used to predict the ionic surfactant monomer concentration, and a simple concentration—based solubility product is assumed to hold between the unbound counterion and monomer, the salinity tolerance of an anionic/nonionic surfactant mixture can be accurately predicted (91). supporting this view of the mechanism of tolerance enhancement by nonionic surfactant. 

The purpose of this paper is to develop realistic specific models of mixed micellization which (i) can describe properties of ionic/nonionic surfactant mixtures and effects of salt (ii) lead to tractable calculations and (iii) can be used for extracting information on micelle mixing and monomer concentrations from the limited experimental data which are usually... 

The purpose of this paper will be to develop a generalized treatment extending the earlier mixed micelle model (I4) to nonideal mixed surfactant monolayers in micellar systems. In this work, a thermodynamic model for nonionic surfactant mixtures is developed which can also be applied empirically to mixtures containing ionic surfactants. The form of the model is designed to allow for future generalization to multiple components, other interfaces and the treatment of contact angles. The use of the pseudo-phase separation approach and regular solution approximation are dictated by the requirement that the model be sufficiently tractable to be applied in realistic situations of interest. 

Self-Emulsiflcation of Vegetable Oil-Nonionic Surfactant Mixtures... 

Wakerly, M.G., Pouton, C.W., Meakin, . J., and Morton, F.S. (1986). Self-emulsification of vegetable oil-nonionic surfactant mixtures A proposed mechanism of action. A.C.S. Symposium, 311, 242-255. 

Butler, E. C Hayes, K. F. Micellar Solubilization of Non-Aqueous Phase Liquid Contaminants by Nonionic Surfactant Mixtures Effects of Sorption, Partitioning and Mixing, Water Research, 1998, 32, 1345-1354. 

Delgado, B., V. Pino, J.H. Ayala, V. Gonzalez, and A.M. Alfonso. 2004. Nonionic surfactant mixtures A new cloud-point extraction approach for the determination of PAHs in seawater using HPLC with fluori-metric detection. Anal. Chim. Acta 518 165-172. 

Rabagliati et al. (14) studied the polymerization of styrene in a three phase system containing an anionic-nonionic surfactant mixture and brine. Both AIBN and potassium persulfate initiators were used. The system was reported to be microemulsion continuous and even multicontinuous. (14). No autoacceleration was observed and the authors concluded that the polymerization exhibits an inverse dependence of the degree of polymerization on initiator concentration, similar to bulk solution polymerization. 

Ahmed NS, Nassar AM, Zaki NN, Gharieb HK. Stability and rheology of heavy crude oil in water emulsions stabilized by an anionic-nonionic surfactant mixture. Petroleum Sci Technol 1999 17 553-576. 

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