Micellar size

Micellar properties are affected by changes in the environment, eg, temperature, solvents, electrolytes, and solubilized components. These changes include compHcated phase changes, viscosity effects, gel formation, and Hquefication of Hquid crystals. Of the simpler changes, high concentrations of water-soluble alcohols in aqueous solution often dissolve micelles and in nonaqueous solvents addition of water frequendy causes a sharp increase in micellar size. 

Flocculation values achieved from turbidity measurements using the light scattering technique showed improvement with nonylphenol ether carboxylic acid (4 mol EO) in particular. The oil solubilization rate has been found to be proportional to the surfactant micellar size [190]. 

Solubilization studies on crude oil by ether carboxylates combined with nonionics have been conducted in the presence of varying amounts of CaCl2 [194]. Good solubility can be obtained when the micellar size is 100 nm and is strongly dependent on the CaCl2 concentration. 

As a result of their size and of specific interactions, hydrophilic macromolecules or solid nanoparticles cause strong changes in micellar size and dynamics, and their structural and dynamic properties are strongly affected. In these cases, the distribution among reversed micelles can be only described by ad hoc models [13,123]. 

Some investigations have emphasized the importance of micellar size as a control parameter of nanoparticle size [224]. It has been suggested that other factors also influence the nanoparticle size, such as the concentration of the reagents, hydration of the surfactant head group, intermicellar interactions, and the intermicellar exchange rate [198,225-228],... 

In the past few years, a range of solvation dynamics experiments have been demonstrated for reverse micellar systems. Reverse micelles form when a polar solvent is sequestered by surfactant molecules in a continuous nonpolar solvent. The interaction of the surfactant polar headgroups with the polar solvent can result in the formation of a well-defined solvent pool. Many different kinds of surfactants have been used to form reverse micelles. However, the structure and dynamics of reverse micelles created with Aerosol-OT (AOT) have been most frequently studied. AOT reverse micelles are monodisperse, spherical water droplets [32]. The micellar size is directly related to the water volume-to-surfactant surface area ratio defined as the molar ratio of water to AOT,... 

Micelles from PS-P2VP-PMMA triblock copolymers dissolved in toluene were reported by Tsitsilianis and Sfika [288]. Since the organic solvent was selective for both the PS and PMMA blocks, these authors observed the formation of spherical micelles with a dense P2VP core, surrounded by PS and PMMA chains in the corona. It was shown that Z and the micellar size were strongly influenced by the length of the P2VP middle block. 

We have shown that polymeric micelles constmcted of block copolymers of poly(ethylene oxide) (PEG) and poly(L-asparate) containing the anticancer dmg (adriamycin, ADR) selectively accumulate at solid tumor sites by a passive targeting mechanism. This is likely due to the hydrophilicity of the outer PEG chains and micellar size (<100 nm) that allow selective tissue interactions [17,18]. Polymeric micelle size ranges are tailored during polymer synthesis steps. Carefully selection of block polymer chemistry and block lengths can produce micelles that inhibit nonselective scavenging by the reticuloendothelial system (RES) and can be utilized as targetable dmg... 

Aggregation Number (Hemimicellar Number) and Micellar Size. 179... 

In order to test further the applicability of 1-pyrene carboxaldehyde as a fluorescent probe, we applied Keh and Valeur s method (4) to determine average micellar sizes of sulfonate A and B micelles. This method is based on the assumption that the motion of a probe molecule is coupled to that of the micelle, and that the micellar hydrodynamic volumes are the same in two apolar solvents of different viscosities. For our purposes, time averaged anisotropies of these systems were measured in two n-alkanes hexane and nonane. The fluorescence lifetime of 1-pyrene carboxaldehyde with the two sulfonates in both these solvents was found to be approximately 5 ns. The micellar sizes (diameter) calculated for sulfonates A and B were 53 5A and 82 lOA, respectively. Since these micelles possesed solid polar cores, they were probably more tightly bound than typical inverted micelles such as those of aerosol OT. Hence, it was expected that the probe molecules would not perturb the micelles to an extent which would substantially affect the micellar sizes measured. 

Lateral Mobility in Alkarylsulfonate Micelles. In order to make a valid comparison of fluidity between sulfonates A and B, the micellar sizes should be comparable. This condition is required so that equal population of pyrene moieties between the two sulfonate systems can be assumed. Alternatively, the requirements might be met if they have equal aggregation numbers. If the above-mentioned (See Section A under "Results") assumptions regarding polar core composition are reasonable, the condition for equal probe population between the two sulfonate micelles can still be reasonably approximated. 

Pyrene carboxaldehyde has utility as a fluorescent probe in some Inverted micellar systems containing solubilized Inorganic species in the polar core. Its fluorescence lifetime is ca. 5 ns thus it is an appropriate probe for measuring micellar sizes which are approximately lOOA. 

Increase of Ry in the presence of MEGA-9 was confirmed for DDdeACr followed by decrease in Ry down to ordinary micellar size as seen in Figure 8. 

We have no measurements of micellar size, since the translation of micelle size into the number of monomers in the micelle is not a simple task and requires assumptions not easily experimentally tested. We are hopeful of extending experimentation in this direction in future research. Table II lists dielectric constants, dipole moments and effective polarities for methanol, 1- and 2-octanol, and water at 25°C. 

Also, micelles are equilibrium systems. What does this mean It means that the final state, for example the average micellar size and all corresponding physical properties, are reached regardless of the pathway used to form them. The final state is thus independent of the mixing order of the components, and does not depend on the previous history of the sample. It is possible to make larger or smaller micelles by changing the environmental parameters (e.g., salt concentration) - and if two... 

Many studies have been carried out on the micellar size of bile salt micelles (3, 4,12,13,17, 20, 25). The experimental conditions and results have been tabulated in a recent review 15). Because these studies were carried out with different bile salts in different laboratories using different techniques at different temperatures, pH, and salt concentrations, values have ranged from monomers (4) to aggregates having nearly 1000 associated molecules (12). This has tended to confuse investigators interested in biological and biochemical aspects of bile salts, who wanted to know the size of the bile salt micelle. The emphasis here is that the type of bile salt, the pH, the temperature, and the counterion concentration all can affect the size and probably the structure of bile salt micelles. 

The dependence of reduced viscosity on concentration is curved upward, which could be interpreted as entanglement of rod-like micelles and/or a strong micellar interaction [47]. The increase in microviscosity results mainly from the growth in micellar size [48]. 

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