Nonionic temperature effect

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)... 

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. 

Caution should be exercised when considering temperature effects on solubilization by micelles, since the aqueous solubility of the solute and thus its micelle/water partition coefLcient can also change in response to temperature changes. For example, it has been reported that although tt solubility of benzoic acid in a series of polyoxyethylene nonionic surfactants increases with temperature, the micelle/water partition coefLci rt, shows a minimum at 2C, presumably due to the increase in the aqueous solubility of benzoic acid (Humphreys and Rhodes, 1968). The increasr in Km with increasing temperature was attributed to an increase in micellar size, as the cloud point temperature of the surfactant is approached (Humphreys and Rhodes, 1968). 

The HLB system used above does not take into consideration the temperature effects. Upon heating, an O/W emulsion prepared with nonionic surfactants inverts to a W/O emulsion because the hydrogen bondings in the polyoxyethylene groups are broken, and the HLB value of the surfactant becomes smaller. The higher the... 

Regarding the surfactant type and rock type, nonionic surfactants have much higher adsorption on a sandstone surface than anionic surfactants (Liu, 2007). However, Liu s initial experiments indicated that the adsorption of nonionic surfactant on calcite was much lower than that of anionic surfactant without the presence of NaaCOs and was of the same order of magnitude as that of anionic surfactant with the presence of Na2C03. Thus, nonionic surfactants might be candidates for use in carbonate formations from the adsorption point of view. The role of salinity is much less important, but the temperature effect is much more important for nonionics than for anionics (Salager et al 1979a). More factors that affect adsorption were discussed by Somasundaran and Hanna (1977). 

Several objectives motivated the extension of ACN studies to light compressible solvents [12]. Initial studies of AOT in such solvents had demonstrated the possibility of intriguing solvent effects [20,21,32], which could be clarified by additional experiments. A second objective was to test the concepts generated from the thermodynamic models that were developed for the AOT-brine-propane system [25,44]. A final objective was to study the behavior of nonionic surfactant systems as a complement to AOT systems. Nonionic systems provide an enhanced opportunity to study temperature effects on surfactant phase behavior, as nonionic surfactants are much more responsive to temperature than the anionic surfactant AOT. 

The temperature effect (58-59,82-83) is mentioned in correlation Eqs. (17) and (18)] as a linearized approximation over the narrow interval of experimental range, and may be considered as a trustworthy estimate for ionic surfactants, whereas is it rather approximate for nonionic ones. 

The temperature affects strongly both the solubihty and the surface activity of nonionic surfactants (165). It is well known that at higher temperatures nonionic surfactants become more oil soluble, which favors the W/0 emulsion. These effects may change the type of emulsion formed at the phase-inversion temperature (166). The temperature effect has numerous implications, two of them being the change in the Gibbs elasticity, Eq, and the interfacial tension, o. 

Nonionic Oxyethylene Surfactants Display Special Temperature Effects 440... 

It is a characteristic feature of ionic surfactant micelliza-tion that the CMC is, to a first approximation, independent of the temperature. The temperature-dependence of the CMC of sodium dodecyl sulfate (SDS), displayed in Figure 19.6, is a good illustration of this. The CMC varies in a non-monotonic way by ca. 10-20% over a wide range. The shallow minimum at around 25°C can be compared with a similar minimum in the solubility of hydrocarbons in water. Nonionic surfactants of the polyoxyethylene type deviate from this behaviour and show typically a monotonic, and much more pronounced, decrease in CMC with increasing temperature. As will be discussed briefly at the end of this chapter, this class of nonionics behaves differently from other surfactants with respect to temperature effects. 

NONIONIC OXYETHYLENE SURFACTANTS DISPLAY SPECIAL TEMPERATURE EFFECTS... 

The potential importance of the temperature effect on surfactant properties has been recognized for some time and led to the concept of using the PIT as a quantitative tool for the evaluation of surfactants in emulsion systems. As a general procedure, emulsions of oil, aqueous phase, and approximately 5% surfactant were prepared by shaking at various temperatures. The temperature at which the emulsion was found to be inverted from o/w to w/o (or vice versa) was then defined as the PIT of the system. Since the effect of temperature on the solubility of nonionic surfactants is reasonably well understood, the physical principles underlying the PIT phenomenon follow directly. 

Zhao G, Khin CC, Chen SB (2005) Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose solutions. J Phys Chem B 109 14198-14204... 

In summary, if one assumes that the hydrophobic core of a micelle is ellipsoidal, then the most consistent analysis of hydration is obtained if one assigns oblate shapes. This was found to be valid for Triton-X-100, at varying temperatures. However, it has recently been suggested [31] that temperature effect on nonionic micelles may also arise from other effects such as critical fluctuations of size. In these systems prolate shape considerations gave negative hydration values, which cannot be acceptable. The data of other nonionic micelles, e.g. NP-10, NP-13 and NP-18, were not as conclusive. However, the analyses of latter systems did provide an indication that useful hydration values were found for oblate ellipsoids, while prolate shapes were not acceptable. 

For nonionic surfactants of the ethylene oxide type, the temperature effect is opposite to that of ionic surfactants, because of the peculiar temperature dependence of the hydration of ethylene oxide groups. As the temperature increases, the ethylene oxide chain loses its hydration water and the spontaneous curvature decreases. To a good approximation, the spontaneous curvature can be approximated by the first term of expansion in series versus temperature "... 

Several references were made above to the term phase inversion temperature. With the exceptions of Eqs. (9.17) and (9.18), however, no specific reference was made to the effect of temperature on the HLB of a surfactant. From the discussions in Chapter 4, it is clear that temperature can play a role in determining the surface activity of a surfactant, especially nonionic amphiphiles in which hydration is the principal mechanism of solubilization. The importance of temperature effects on surfactant solution properties, especially the solubility or cloud point of nonionic surfactants, led to the evolution of the concept of using that property as a tool for predicting the activity of such materials in emulsions. Since the cloud point is defined as the temperature, or temperature range, at which a given amphiphile loses sufficient solubility in water to produce a normal surfactant solution, it was assumed that such a temperature-driven transition would also be reflected in the role of the surfactant in emulsion formation and stabilization. 

Other properties of association colloids that have been studied include calorimetric measurements of the heat of micelle formation (about 6 kcal/mol for a nonionic species, see Ref. 188) and the effect of high pressure (which decreases the aggregation number [189], but may raise the CMC [190]). Fast relaxation methods (rapid flow mixing, pressure-jump, temperature-jump) tend to reveal two relaxation times t and f2, the interpretation of which has been subject to much disagreement—see Ref. 191. A fast process of fi - 1 msec may represent the rate of addition to or dissociation from a micelle of individual monomer units, and a slow process of ti < 100 msec may represent the rate of total dissociation of a micelle (192 see also Refs. 193-195). 

AH detergent proteases are destabilized by linear alkylbenzenesulfonate (LAS), the most common type of anionic surfactant in detergents. The higher the LAS concentration and wash temperature, the greater the inactivation of the enzyme. The presence of nonionic surfactants, however, counteracts the negative effect of LAS. Almost aH detergents contain some nonionic surfactant therefore, the stabHity of proteases in a washing context is not problematic. 

Earlier formulations contained mainly chlorine bleach, metasiUcates, triphosphate, and nonionic surfactants. Modem manufacturers have switched to more compHcated formulations with disiUcates, phosphates or citrate, phosphonates, polycarboxylates, nonionic surfactants, oxygen bleach, bleach activator, and enzymes. The replacement of metasiUcates by disilicates lowers pH from approximately 12 to 10.5, at 1 g ADD/L water. The combined effect of decreased pH, the absence of hypochlorite, and the trend toward lower wash temperatures has paved the way for the introduction of enzymes into ADDs. Most ADD brands in Europe are part of the new generation of ADD products with enzymes. The new formulations are described in the patent hterature (55—57). 

R. Zana, C. Weill. Effect of temperature on the aggregation behavior of nonionic surfactants in aqueous solutions. J Physique Lett 46 L953-L960, 1985. 

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