Aqueous surfactant solution properties

The mechanisms that affect heat transfer in single-phase and two-phase aqueous surfactant solutions is a conjugate problem involving the heater and liquid properties (viscosity, thermal conductivity, heat capacity, surface tension). Besides the effects of heater geometry, its surface characteristics, and wall heat flux level, the bulk concentration of surfactant and its chemistry (ionic nature and molecular weight), surface wetting, surfactant adsorption and desorption, and foaming should be considered. 

Surfactants have been widely used to reduce the interfacial tension between oil and soil, thus enhancing the efficiency of rinsing oil from soil. Numerous environmentally safe and relatively inexpensive surfactants are commercially available. Table 18.6 lists some surfactants and their chemical properties.74 The data in Table 18.6 are based on laboratory experimentation therefore, before selection, further field testing on their performance is recommended. The Texas Research Institute75 demonstrated that a mixture of anionic and nonionic surfactants resulted in contaminant recovery of up to 40%. A laboratory study showed that crude oil recovery was increased from less than 1% to 86%, and PCB recovery was increased from less than 1% to 68% when soil columns were flushed with an aqueous surfactant solution.74-76... 

Exploiting the properties of aqueous surfactant solutions in which the surfactants aggregate to form micelles consisting of apolar cores comprised of the hydrophobic tail groups stabilized by coronae formed by the hydrophilic surfactant heads (Fendler and Fendler, 1975 Bunton, 1991). The apolar core plays the role of the organic solvent, whereas the palisade layer can provide a medium of intermediate polarity. 

Figure 3.21 Changes in physical properties of an aqueous surfactant solution at concentrations near the critical micelle concentration, shown here as a narrow range of concentrations.

Figure 2.2 Physical properties of aqueous surfactant solution as a function of surfactant concentration.

Washes. Several types of solutions or liquids can be used to collect handwash samples, including various types of aqueous surfactant solutions, and neat isopropanol or ethanol. The physico-chemical properties of the pesticide should guide selection of the rinse solvent, especially the octanol-water partition coefficient... 

Water soluble polymers are frequently incorporated in aqueous surfactant solutions in many domestic and technological applications (in formulations such as shower gels and hair shampoos), as viscosity modifiers, stabilisers and deposition aids. Water soluble polymers often interact strongly with surfactants in aqueous solution, giving rise to a rich pattern of behaviour in properties such as surface tension. The bulk properties of a variety of polymer/... 

From the same laboratory, another report48 describes the use of this approach to prepare PPy/poly(alkyl methacrylate). In this case, a chloroform solution of poly(alkyl methacrylate) and pyrrole is dispersed in an aqueous surfactant solution whereupon the oxidant is added. The PPy deposits on the host polymer, and again a nonsolvent is used to precipitate the composite. The composites can then be hot-pressed to obtain films or other objects. Compared to cold pressing, hot pressing improves the mechanical properties but decreases the conductivities. In the hot-pressed materials, a distinct PPy phase could not be observed. 

The solubility of hydrocarbons in water is greatly enhanced by the presence of surfactants. Similarly, the addition of hydrocarbons to aqueous surfactant solution induces change in the physical properties of the surfactant (24, 25). Thus, the quantitative analysis of the partitioning of hydrocarbons between micelle interior and aqueous phase has been a subject of numerous studies. Among the many techniques used to determine the partitioning, only fluorescence (26), FT-pulsed-gradient spin echo NMR (27), and recently, Raman spectroscopy (28) have demonstrated sufficient sensitivity. 

Fig. 4 Some properties of aqueous surfactant solutions related to CMC.

Feng,Kunieda, H., Izawa, T., and Sakai, T. (2004) Effect of novel alkanolamides on the phase behavior and surface properties of aqueous surfactant solutions. /. Dispersion Sci. Tedinol, 25,1 10. 

For any aqueous surfactant solution, there is a relatively small range of concentrations below which virtually all surfactant is present as monomers, and above which virtually all additional surfactant is present in micellar form. This micellization phenomenon causes significant changes in the bulk physical properties of the solution. The cmc is an important parameter which deserves careful attention in order to minimize uncertainties in K m measurement. 

Despite their potential application, the wetting properties of aqueous surfactant solutions on superhydrophobic (SH) solid surfaces have been rarely investigated. In this work single surfactant solutions and binary mixtures of non-ionic and ionic surfactants have been studied in contact with textured and non-textured surface coatings obtained utilizing nanoparticles and a fluorinated polymer. 

The adhesion of particles to oily surfaces can be changed by varying the time of exposure to aqueous surfactant solutions and also by the selection of surfactants with specific properties. As an example, we have determined adhesion numbers in the detachment of spherical glass particles 30 /xm in diameter (immersion method) from an oily surface, with various soak times in the liquid [86] ... 

A study of immiscible liquid/liquid displacement on model systems, paraffin oil/aqueous surfactant solutions in glass capillary tubes led to the conclusion that flow and wetting properties cannot be treated separately. Even though there is a correlation between static and dynamic contact angles, the validity of this relation is restricted to relatively low surfactant concentrations. 

The unusual properties of aqueous surfactant solutions can be ascribed to the presence of a hydrophilic head group and a hydrophobic chain (or tail) in the molecule. The polar or ionic head group usually interacts strongly with an aqueous environment, in which case it is solvated via dipole-dipole or ion-dipole interactions. In fact, it is the nature of the polar head group which is used to divide surfactants into different categories, as illustrated in Table 2. In-depth discussions of surfactant structure and chemistry can be found in references [1, 2, 8, 34, 35]. 

Emulsion polymerization of pyrrole was also used to prepare blends of polypyrrole with a poly(alkyl methacrylate) [95]. A chloroform solution of a poly-(alkyl acrylate) and pyrrole was dispersed in an aqueous surfactant solution generating an emulsion. An aqueous solution of an oxidant was added to the emulsion with stirring, polymerizing pyrrole. The precipitated blend could be hot pressed in the form of films with conductivities of 6-7Scm . The curve for the variation of the conductivity of the blend with the oxidant/pyrrole ratio shows a maximum at a ratio of two with subsequent decrease. However, the yield increases to nearly 100% up to a ratio of four. The percolation threshold is approximately 10 wt% of pyrrole. The type and the concentration of the surfactant also affect the yield and conductivity. The mechanical properties of the blend depends on the number of carbons in the alkyl chain of the insulating polymer host. The strain at break of hot-pressed films increases and the stress at break decreases in the direction methyl, ethyl, butyl (Figure 18.3). This is an example where the mechanical properties of the conductive blend could be tailored according to the alkyl substituent in the poly(alkyl methacrylate) used in its preparation. 

Surface Tension Properties of Aqueous Surfactant Solutions... 

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