Surfactants system 546 INDEX

Micellar and pre-micellar solutions of methanol in triolein were studied with three different surfactant systems using 2-octanol as a co-surfactant. Surfactants evaluated by viscosity, conductivity, density, refractive index and particle size data along with polarizing microscopic examinations were bis(2-ethylhexyl) sodium sulfosuccinate, triethylammonium linoleate and tetradecyldimethylammonium linoleate. Data show phase equilibria regions of liquid crystalline phases as well as micellar solutions. All systems were effective for solubilizing methanol in triolein. The order of effectiveness for water tolerance is Tetradecyldimethylammonium linoleate>... 

Single Surfactant Systems. Relative intensity results for an equilibrium film of the block copolymer B1 in n-decane sandwiched between two water droplets at 25°C, are shown in Table II. The intensity was independent of the bulk polymer concentration within the accuracy of measurement. Assuming a constant film refractive index this implies that the film thickness is independent of surfactant concentration, and an average value of J was used for the calculation of film thickness. Coalescence occurs below a concentration of 0.1 g dm, presumably because there is insufficient... 

Apart from the fact that the use of the HLB system is limited as it is based on the observation of creaming or separation of the emulsions, as an index of instability the HLB system also neglects the effects of surfactant concentration on stability (26) and of course it is irrelevant to the particular problems with multiple emulsion systems. Nevertheless, it provides a useful approach to the choice of optimal surfactant system. In general, in a w/o/w emulsion, the optimal HLB value of the primary surfactant will be in the range 2-7 and in the range 6-16 for the secondary surfactant. Equilibration of the systems after mixing will undoubtedly result in the transfer of surfactant between the aqueous and nonaqueous components. Saturation of the phases with the two surfactants used should prevent instability during this equilibration. 

Strkcttire inflkence. The specificity of interphase transfer in the micellar-extraction systems is the independent and cooperative influence of the substrate molecular structure - the first-order molecular connectivity indexes) and hydrophobicity (log P - the distribution coefficient value in the water-octanole system) on its distribution between the water and the surfactant-rich phases. The possibility of substrates distribution and their D-values prediction in the cloud point extraction systems using regressions, which consider the log P and values was shown. Here the specificity of the micellar extraction is determined by the appearance of the host-guest phenomenon at molecular level and the high level of stmctural organization of the micellar phase itself. 

Phosphoric acid ester was used as a model for the estimation of concentration of a reagent in an adsorbed layer by optical measurements of the intensity of a beam reflecting externally from the liquid-liquid interface. The refractive index of an adsorbed layer between water and organic solution phases was measured through an external reflection method with a polarized incident laser beam to estimate the concentration of a surfactant at the interface. Variation of the interfacial concentration with the bulk concentration estimated on phosphoric acid ester in heptane and water system from the optical method agreed with the results determined from the interfacial tension measurements... 

Interpretation of NMR well logs is usually made with the assumption that the formation is water-wet such that water occupies the smaller pores and oil relaxes as the bulk fluid. Examination of crude oil, brine, rock systems show that a mixed-wet condition is more common than a water-wet condition, but the NMR interpretation may not be adversely affected [47]. Surfactants used in oil-based drilling fluids have a significant effect on wettability and the NMR response can be correlated with the Amott-Harvey wettability index [46]. These surfactants can have an effect on the estimation of the irreducible water saturation unless compensated by adjusting the T2 cut-off [48]. 

The greatest disadvantage of all detector systems such as, e.g. FID, UV, diode array detection (UV-DAD), FL, refractory index (RI), light scattering detector (LSD) or conductivity, applied in combination with GC, LC or CZE, is that they only provide an electric signal at the detector. The retention time alone of standard compounds, if available, is not sufficient for a reliable identification. LC separation of surfactant-containing extracts may often result in non-reproducible retention... 

Other detection systems, such as conductivity detector or refractive index detection are generally applicable for the determination of common anionic surfactants [1]. However, they are less sensitive than other techniques and are used more often for the characterisation of pure surfactants, than for their determination at low concentrations. 

For the cationic surfactants, the available HPLC detection methods involve direct UV (for cationics with chromophores, such as benzylalkyl-dimethyl ammonium salts) or for compounds that lack UV absorbance, indirect photometry in conjunction with a post-column addition of bromophenol blue or other anionic dye [49], refractive index [50,51], conductivity detection [47,52] and fluorescence combined with postcolumn addition of the ion-pair [53] were used. These modes of detection, limited to isocratic elution, are not totally satisfactory for the separation of quaternary compounds with a wide range of molecular weights. Thus, to overcome the limitation of other detection systems, the ELS detector has been introduced as a universal detector compatible with gradient elution [45]. 

Fig. 10 relates the composite extraction index (see above) obtained in the low-shear aqueous test system for these Tween surfactants, and adhesion tensions measured against various solids. Adhesion tensions against platinum and bitumen saturated pyrophyllite are irregularly related to tar sand extraction, while the adhesion tension against a fresh pyrophyllite surface is linearly (inversely) related to tar sand extraction. This is the first linear correlation between a measurable property of a surfactant solution and tar sand extraction which we have been able to obtain, and there appears to be no such finding in the literature. Fig. 11 gives the relations between extraction of bitumen with the paddle mill, solvent-aqueous-surfactant extraction and adhesion tensions measured against platinum, bitumen saturated pyrophyllite and hydrated (48 hours in water) pyrophyllite. 

Even the traditional methods discussed in this chapter can be used for concentrated dispersions through contrast matching. For example, silica particles coated with silane coupling agents in a refractive index-matched mixture of ethanol and toluene can be used in combination with visible probe particles to study the dynamics of particles in dense systems. In the case of microemulsions (Chapter 8), selective deuteration of a component (oil, water, or surfactant) can be used in neutron scattering experiments even to measure the curvature of the oil-water interface. 

In the last 10-15 years, neutron reflectometry has been developed into a powerful technique for the study of surface and interfacial structure, and has been extensively applied to the study of surfactant and polymer adsorption and to determine the structure of a variety of thin films [14, 16]. Neutron reflectivity is particularly powerful in the study of organic systems, in that hydrogen/deu-terium isotopic substitution can be used to manipulate the refractive index distribution without substantially altering the chemistry. Hence, specific components can be made visible or invisible by refractive index matching. This has, for example, been extensively exploited in studying surfactant adsorption at the air-solution interface [17]. In this chapter, we focus on the application of neutron reflectometry to probe surfactant adsorption at the solid-solution interface. 

Most cubic phases in lipid-water systems exhibit unit cell parameters not larger than 20 mn, while the imit cell of cubic membranes is usually larger than 100 nm. Some exceptioi have been apparently found [131, 132] although at this stage such findings should be treated with caution, as the determination of lattice parameters is dependent on the indexing of diffraction patterns, based only on a small niunber of reflections. Further, in lipid-protein-water, lipid-poloxamer-water and lipid-cationic surfactant-water systems, cubic phases with cell parameters of the order of 50 nm have been observed [56,127, 128]. Due to the small number of reports dealing with the... 

For the high-quality MCM-41 sample, XRD can give more than four hkO diffraction peaks. Figure 8.13 shows the XRD pattern of high-quality MCM-41 made from an extremely low surfactant-concentration system.[110]. These peaks, except the first one, are very weak. The position of diffraction peaks can be indexed with 2-D hexagonal p6mm symmetry. 

The results with isohexadecane are summarised in Table 14.2. As with the hexadecane system, the droplet size and polydispersity index were decreased with increases in surfactant concentration. Nanoemulsions with droplet radii of 25-80run were obtained at 3-8% surfactant concentration. It should be noted, however, that nanoemulsions could be produced at lower surfactant concentration when using isohexadecane, when compared to results obtained with hexadecane. This could be attributed to the higher solubility of isohexadecane (a branched hydrocarbon), the lower HLB temperature, and the lower interfacial tension. 

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