Micellar solution shape

Since their effective diffusivities are of the same magnitude as those of micellar solutions, the hquid crystalUne phases, though viscous, do not significantly hinder surfactant dissolution for these rather hydrophihc surfactants. Indeed, a drop of Ci2(EO)6 having Ro = 78 pm dissolved completely in only 16 s at 30 °C. Rapid dissolution is favored because free energy decreases as the surfactant is transferred from the Hquid surfactant phase L2 to liquid crystals) to aqueous micellar solution and the aggregate shape approaches that of a dilute Li phase, where its free energy is minimized at this temperature. 

The alcohol formed on hydrolysis of a betaine ester surfactant has strong effects on the shape of its aggregates and its phase behavior. In a micellar solution of dodecyl betainate, addition of 10 to 20% of dodecanol causes a significant aggregate growth (higher additions cause phase separation) [29]. In... 

At low water content from vv = 2 to 5.5, a homogeneous reverse micellar solution (the L2 phase) is formed. In this range, the shape of the water droplets changes from spheres (below ir = 4) to cylinders. At tv — 4, the gyration radius has been determined by SAXS and found equal to 4 nm. Syntheses in isolated water-in-oil droplets show formation of a relatively small amount of copper metallic particles. Most of the particles are spherical (87%) with a low percentage (13%) of cylinders. The average size of spherical particles is characterized by a diameter of 12 nm with a size polydispersity of 14%. 

This CE method provides an efficient approach for rapid and effective separation of serum conjugated BAs with an analysis time of 8 min. It is important to mention that each micellar solution plays an important role in the analysis use of 20 mM SDS is to modify the electro-osmotic flow, whereas solubility of glycine-conjugated BAs and the peak shape of all BAs are maintained with 20% acetonitrile and the neutral pH of the phosphate buffer. The optimum condition for baseline separation is achieved with the addition of 8 mM CD. 

In two-component systems of association of colloid and water the sequence of phases, as the water content decreases, is micellar solution - hexagonally packed polar rods complex phases with rod-shaped aggregates lamellar mesophase D - crystalline surfactant. Some of these steps may be absent, depending, for example, on the temperature. 

Assuming that different polymorphisms can be found in the extractant systems, a better understanding also comes from other phase-separation mechanisms studied in classical amphiphilic systems such as soaps and lipids. The first, largely described here, is the phase separation resulting from increased attractive interactions. The second occurs when a sphere-to-rod transition is observed for the shape of the aggregates. The attraction between cylinders is higher than between spheres when attraction is dominated by van der Walls (VdW) forces between polar cores (119). For micellar solutions (reverse or not), the liquid-liquid phase transition cannot be unambiguously attributed to either shape or attractive interactions only, as it appears that these two effects coexist in nonionic surfactants solutions (91, 120-123). 

The confinement of a relatively large number of dye molecules in the small volume of a nanoparticle may trigger collective phenomena otherwise not observable in bulk solution. This has been demonstrated by Prasad and coworkers in the case of an ORMOSIL pH sensor.69 The PEBBLEs contain a naphthalenylvinylpyridine derivative (NVP) as pH-sensitive fluorescent dye which has been functionalized with a triethoxysilane anchor by reaction with an excess of (3-isocyanatopropyl)triethoxysi-lane (ICTES). The sol-gel polymerization in aqueous micellar solution of the NVP-ICTES derivative with VTES gives spherically shaped 33 nm silica nanoparticles in which the dye is covalently linked to the silica matrix and uniformly distributed in the nanoparticle volume. The NVP dye responds ratiometrically to protons, with a... 

Perhaps the most important distinction between classical solids and classical liquids is that the latter quickly shape themselves to the container in which they reside, while the former maintain their shape indefinitely. Many complex fluids are intermediate between solid and liquid in that while they maintain their shape for a time, they eventually flowr They are solids at short times and liquids at long times hence, they are viscoelastic. The characteristic time required for them to change from solid to liquid varies from fractions of a second to days, or even years, depending on the fluid. Examples of complex fluids with long structural or molecular relaxation times include glass-forming liquids, polymer melts and solutions, and micellar solutions. 

Disordered solutions of spherical micelles are not particularly viscoelastic, or even viscous, unless the volume fraction of micelles becomes high, greater than 30% by volume. Figure 12-7, for example, shows the relative viscosity (the viscosity divided by the solvent viscosity) as a function of micellar volume fraction for a solution of hydrated micelles of lithium dodecyl sulfate in water. Qualitatively, these data are reminiscent of the viscosity-volume-fraction relationship for suspensions of hard spheres, shown as a dashed line (see Section 6.2.1). The micellar viscosity is higher than that of hard-sphere suspensions because of micellar ellipsoidal shape fluctuations and electrostatic repulsions. 

We have examined the stmcture of both ionic and nonionic micelles and some of the factors that affect their size and critical micelle concentration. An increase in hydrophobic chain length causes a decrease in the cmc and increase of size of ionic and nonionic micelles an increase of polyoxyethylene chain length has the opposite effect on these properties in nonionic micelles. About 70-80% of the counterions of an ionic surfactant are bound to the micelle and the nature of the counterion can influence the properties of these micelles. Electrolyte addition to micellar solutions of ionic surfactants reduces the cmc and increases the micellar size, sometimes causing a change of shape from spherical to ellipsoidal. Solutions of some nonionic surfactants become cloudy on heating and separate reversibly into two phases at the cloud point. 

Optically transparent micellar solutions are often able to dissolve considerable quantities of a substance molecular insoluble in the pure solvent. The transparency of such a solution is not affected by this. The solubilisation is controlled by the shape and size of the micelles which determine the amotmt of components incorporated into the interior of the micelles (Schulman etal. 1959). 

Among various relaxation spectrometry methods of liquid surface layers the transverse capillary waves has been used most frequently for micellar solutions [96 - 101]. The shape of the concentration dependence of the wavelength is the same for all investigated cationic, anionic and nonionic surfactants and resembles the corresponding dependence of surface tension. Figure 16 shows as an example the experimental results for solutions of SDS [96]. 

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