Surfactants Temperature dependence

Liquid Third Phase. A third Hquid with coUoidal stmcture has been a known component in emulsions since the 1970s (22) for nonionic surfactants of the poly(ethylene glycol) alkylaryl ether type. It allows low energy emulsification (23) using the strong temperature dependence of the coUoidal association stmctures in the water—surfactant—hydrocarbon systems. 

With increasing water content the reversed micelles change via swollen micelles 62) into a lamellar crystalline phase, because only a limited number of water molecules may be entrapped in a reversed micelle at a distinct surfactant concentration. Tama-mushi and Watanabe 62) have studied the formation of reversed micelles and the transition into liquid crystalline structures under thermodynamic and kinetic aspects for AOT/isooctane/water at 25 °C. According to the phase-diagram, liquid crystalline phases occur above 50—60% H20. The temperature dependence of these phase transitions have been studied by Kunieda and Shinoda 63). 

A positive value of ME means that the insertion of a hetero atom or group makes the molecule more lipophilic. If ME is negative, the hetero surfactant is more hydrophilic. In general, hetero atom insertion hydrophilizes the surfactant molecule as does the shift of the hetero group to the middle of the carbon chain [71]. ME values are temperature-dependent. / and ME values can also be useful to take into account the influence of various cations on the critical micelle concentration. 

Viscosity of surfactant solutions depends on the kind of solution, shear rate, temperature and concentration. Figure 2.51 shows the effect of shear rate U5 on shear... 

The interfacial tension behavior between a crude oil (as opposed to pure hydrocarbon) and an aqueous surfactant phase as a function of temperature has not been extensively studied. Burkowsky and Marx T181 observed interfacial tension minima at temperatures between 50 and 80°C for crude oils with some surfactant formulations, whereas interfacial tensions for other formulations were not affected by temperature changes. Handy et al. [191 observed little or no temperature dependence (25-180°C) for interfacial tensions between California crude and aqueous petroleum sulfonate surfactants at various NaCI concentrations. In contrast, for a pure hydrocarbon or mineral oil and the same surfactant systems, an abrupt decrease in interfacial tension was observed at temperatures in excess of 120°C 1 20]. Non ionic surfactants showed sharp minima of interfacial tension for crude... 

The Yl/A isotherms of the racemic and enantiomeric forms of DPPC are identical within experimental error under every condition of temperature, humidity, and rate of compression that we have tested. For example, the temperature dependence of the compression/expansion curves for DPPC monolayers spread on pure water are identical for both the racemic mixture and the d- and L-isomers (Fig. 13). Furthermore, the equilibrium spreading pressures of this surfactant are independent of stereochemistry in the same broad temperature range, indicating that both enantiomeric and racemic films of DPPC are at the same energetic state when in equilibrium with their bulk crystals. 

The S-form can be obtained by treating Copper Phthalocyanine Blue in benzene or toluene with aqueous sulfuric acid in the presence of a surfactant [21], The e-phase is produced by comminution of the a-, 7-, or 8-modification, for instance in a planetary ball mill. The mill base is then aftertreated in an organic solvent at elevated temperature. It is important to realize that the temperature, depending on the solvent, must be kept below the transition temperature at which the e-phase converts to the (3-modification (30 to 160°C). The e-modification is made best from the 7-phase, and the most preferred solvents are alcohols [22], For the industrially hitherto insignificant tt, X, and R-forms of Copper Phthalocyanine Blue (see [1], Vol. II, 34-35). 

Most of the studies on thermodynamics of mixed micellar systems are based on the variation of the critical micellar concentration (CMC) with the relative concentration of both components of the mixed micelles (1-4). Through this approach It Is possible to obtain the free energies of formation of mixed micelles. However, at best, the sign and magnitude of the enthalpies and entropies can be obtained from the temperature dependences of the CMC. An Investigation of the thermodynamic properties of transfer of one surfactant from water to a solution of another surfactant offers a promising alternative approach ( ), and, recently, mathematical models have been developed to Interpret such properties (6-9). 

Therefore, the temperature dependence of mixed micelle properties predicted from it are incorrect and there may be surfactant mixtures for which it does not even work empirically. This is a totally unsatisfactory state of affai rs. 

T he phase equilibria of ionic surfactants combined with water and an A amphiphilic substance such as a long chain alcohol, carboxylic acid, or ester have been investigated in detail for a long time (1, 2). The nonionic surfactants have not attracted as much interest despite the fact that they are suitable models for illustrating the association conditions which are responsible for the structure and function of biomembranes they also present interesting problems in their temperature dependent interaction with water and hydrocarbons. 

The presence of a liquid crystalline phase at high surfactant concentrations has been shown by Shinoda (31), but the method of presentation renders the evaluation of the temperature dependence of necessary emulsifier concentrations to obtain the liquid crystalline phase difficult. Although several phase diagrams of the system (water, emulsifier, and nonionic surfactant) have been published (4, 45, 46, 47, 48), no results have been given on the relation between the surfactant phase and the lamellar liquid crystalline phase in these systems. 

K. Kuriyama, Temperature dependence of micellar weight of nonionic surfactant in the presence of various additives, Part 2, Addition of sodium chloride and calcium chloride, Kolloid Z.Z. Polym. 181 (1962) 144-149. 

Muller, N. 1993. Temperature dependence of critical micelle concentrations and heat capacities of micellization for ionic surfactants. Langmuir 9, 96-100... 

It is an everyday experience that calcium soaps have a low aqueous solubility while many surfactants with monovalent counterions have an extremely high solubility. As for other compounds, the solubility is to a great extent given by conditions in the solid phase, but for surfactants the strongly cooperative association produces the peculiar temperature dependence of solubility schematized in Fig. 2.8. The so-... 

Fig. 2.8. Temperature dependence of surfactant solubility in the region of the Krafft point. (From Ref.2 )...

Kitahara115,116,119,121 arrives at similar conclusions with fatty acid salts of higher aliphatic primary amines in benzene. Large amounts of data on cationic surfactants, particularly, their temperature dependent aggregation were collected by Kertes and coworkers109 n0, 11 141. In a number of cases thermodynamic data were calculated from this temperature dependence119. However, frequently the dependence of the aggregation number on the temperature was not duly considered which makes the derived quantities less useful. 

A quite similar behaviour is found with nonionic surfactants in nonpolar media. Debye and Coll33 studied the temperature dependent aggregation of a-monogly-cerides, in particular, monocaprin (C10) in carbontetrachloride at 23 and 38 °C. 

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