Solubilization in micellar

Transition Metal Catalysts Solubilized In Micellar Aggregates... 

When CTAC is solubilized in micellar solution with sulfide S2- ions, at low water contents (w < 10), the presence of CTAC induces a strong decrease in CdS nanocrystallite size. For a given water content, the absorption spectra are blue shifted when the syntheses are performed in the presence of CTAC compared to that obtained in its absence. The temporal evolution of absorption at 250 nm is approximated to nucleation rate of CdS. It slows down in the presence of CTAC. This blue shift is more pronounced at low water content and high CTAC concentration. Hence it is observed a decrease in the particle size by increasing CTAC concentration. This can be related to the decrease in the intermicellar potential in the presence of CTAC (64). 

When CTAC is solubilized in micellar solution with cadmium Cd2+ ions, a better resolution in the excitonic peak with increasing CTAC concentration is observed. The sharp peak is more intense for low water content and for high CTAC concentration. This clearly shows a narrow size distribution. 

Double Layer Interactions and Interfacial Charge. Schulman et al (42) have proposed that the phase continuity can be controlled readily by interfacial charge. If the concentration of the counterions for the ionic surfactant is higher and the diffuse electrical double layer at the interface is compressed, water-in-oil microemulsions are formed. If the concentration of the counterions is sufficiently decreased to produce a charge at the oil-water interface, the system presumably inverts to an oil-in-water type microemulsion. It was also proposed that for the droplets of spherical shape, the resulting microemulsions are isotropic and exhibit Newtonian flow behavior with one diffused band in X-ray diffraction pattern. Moreover, for droplets of cylindrical shape, the resulting microemulsions are optically anisotropic and non-Newtonian flow behavior with two di-fused bands in X-ray diffraction (9). The concept of molecular interactions at the oil-water interface for the formation of microemulsions was further extended by Prince (49). Prince (50) also discussed the differences in solubilization in micellar and microemulsion systems. 

The approach to the thermodynamics of solubilization in micellar solutions is based on the determination of a given partial molar property of the solute (volume, enthalpy, heat capacity, compressibility) as a function of the surfactant content. The simplest approach is to use the pseudophase model. The partial molar quantity, L will thus be an average value of Y in the micellar and aqueous phases, as described by... 

Gao, Z., Wasylishen, R.E., and Kwak, J.C.T., An NMR paramagnetic relaxation method to determine distribution coefficients of solubilization in micellar systems, J. Phys. Chem., 93, 2190, 1989. Treiner, C., The partitioning of neutral solutes between micelles and water as deduced from critical micelle concentration determinations, in Solubilization in Surfactant Aggregates, Christian, S.D. and Scamehorn, J.R, Eds., Marcel Dekker, New York, 1995, chap. 12. 

Depending on the relative rates of the chemical and diffusion steps, the reaction can proceed in the kinetic, diffusion, or mixed regime, the entire process being controlled by the rate of the chemical step, a diffusion process, or by both kinetics and diffusion. Thus, under very good hydrodynamic conditions, e.g., upon vigorous agitation, the influence of the diffusion can be substantially eliminated and the kinetic results can be used to discuss the reaction mechanism. This conclusion is not always true, and the use of typical surfactant micellar aqueous solutions with extractants dissolved (solubilized) in micellar pseudophase (micelles) and inorganic species dissolved in aqueous pseudophase mimic the extraction systems effectively and the diffusion processes are totally eliminated. 

Solubilization in Micellar Solutions (of Organic Water Insoluble Molecules) in Micelles... 

When mixed micelles are enriched in lecithin, the particles become bigger and the solutions manifest the Tyndall phenomena[8] mixed micelles are transformed into vesicles so that the solution shows a new phase (liquid crystals). In this manner a solution resembling bile can present different phases in relation to the molar percentage composition of the three components (Ch, Lee, and BS) and in particular solid (Ch crystals), liquid (micelles), and liquid crystalline phases may be present[12]. Cholesterol is solubilized in micellar and liquid-crystalline phases and this possibility has been demonstrated for some hydrophilic bile acids such as ursodeoxycholic acid[ll]. 

Although much of this book is concerned with solubilization in micellar systems, there is a need to discuss the phenomenon of hydrotropy, as there is now a considerable body of literature on the pharmaceutical aspects of the subject. As has been discussed, hydrotropy is the term reserved for the action of increasing the solubility of a solute by a third substance which is not highly surface active - at least one which does not form micelles at low concentrations. The mechanism of... 

Fluorescence kinetics of ArOH and ArO in micellar solutions of surfactants with various charges was studied by conventional single photon counting method using numerical deconvolution of decay curves. Concentrations of anionic surfactant - SDS ( 0.1 M ), cationic surfactant - DTAB (0.05 M ) and nonionic surfactant - Triton X-305 and Brij 35 (0.01 M ) were chosen by such a way, that more than 99% of hydro-xycompounds were solubilized in micellar phase and protoly-tic photoreaction take place nearly completely in this phase [11-14]. 

More hydrophobic additives such as free fatty acids and their esters and amides, long-chain monohydric alcohols, and nitriles may have an even more dramatic effect on the phase behavior of a surfactant due to solubilization phenomena. The general subject of solubilization in micellar systems is discussed in Chapter 6. For now, we will focus on the effects that the presence of solubilized materials may have on liquid crystal phases. 

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