Micellization manifestations

Long-chain fatty acids are insoluble in water, and their titration curves are concentration-dependent because of the formation of organized aggregates (acid soaps, soap micelles, fatty acid precipitates) which concentrate protons at the surface. At concentrations above the critical micellar concentration, solutions of long-chain fatty acid soaps manifest a diprotic curve when they are titrated from pH 10 to 4 (23). The first... 

In other media like micelles, cyclodextrin, binary solvent mixtures, and proteins (47-55), lifetime distributions are routinely used to model the decay kinetics. In all of these cases the distribution is a result of the (intrinsic or extrinsic) fluorescent probe distributing simultaneously in an ensemble of different local environments. For example, in the case of the cyclodextrin work from our laboratory (53-55), the observed lifetime distribution is a result of an ensemble of 1 1 inclusion complexes forming and coexisting. These complexes are such that the fluorescent probe is located simultaneously in an array of environments (polarities, etc.) in, near, and within the cyclodextrin cavity, which manifest themselves in a distribution of excited-state lifetimes (53-55). In the present study our experimental results argue for a unimodal lifetime distribution for PRODAN in pure CF3H. The question then becomes, how can a lifetime distribution be manifest in a pure solvent ... 

Adsorption of water is accompanied with swelling of wood. Since cellulose constitutes almost 50% of the wood substance, its fractional contribution to sorption is the highest. Swelling of wood is thus manifested by the adsorption of water by hydroxyl groups located on surface of micells and amorphous regions of cellulose, crystalline zones being impenetrable. Reduction in... 

Hexapus in water solubilizes cholesterol, phenol blue (Kassoc = 1.0 x 104 M 1), naphthalene, and hydrophobic esters. Thus, hexapus seems non-selective in its binding characteristics (just like micelles). Universal binding has the advantage that almost any water-insoluble compound can be collected by the host molecule without regard to subtle structural variations. On the other hand, potential catalysts based on hexapus and other multi-armed systems would not be expected to manifest high specificity. Flexible chains do not lend themselves to a precise fit. 

Consequently, new investigations dealing with reactions in micellar solutions composed of functional surfactants, or mixtures of inert and functional surfactants, continue to appear in the literature. An interesting study of acid-catalyzed hydrolysis of 2-(p-tetradecyloxyphenyl)-l,3-dioxolane (p-TPD) in aqueous sodium dodecyl sulfate (SDS) solutions has been reported [13]. In this case,/ -TPD behaves as a non-ionic functional surfactant and apparently forms non-ideal mixed micelles with the anionic surfactant (SDS). Based on the observed kinetic data, the authors propose that, at elevated temperatures, the thermodynamic non-ideality results in the manifestation of two populations of micelles, one rich in SDS and the other rich in/>-TPD. 

Robinson, 1969a). It is probable that the hydrophobic nature of the phenyl groups of p-nitrophenyl diphenyl phosphate results in deep penetration of the neutral ester in the Stern layer, thus shielding the phosphoryl group from nucleophilic attack. Unlike other reactions between nucleophiles and neutral substrates catalyzed by cationic micelles (Bunton and Robinson, 1968, 1969a) and the hydrolysis of dinitrophenyl phosphate dianions in the presence of cationic micelles (Bunton et al., 1968), the catalysis of the hydrolysis of -nitrophenyl diphenyl phosphate by CTAB arises from an increase in the activation entropy rather than from a decrease in the enthalpy of activation. The Arrhenius parameters for the micelle-catalyzed and inhibited reactions are most probably manifestations of the extensive solubilization of this substrate. However, these parameters can be composites of those for the micellar and non-micellar reactions and the eifects of temperature on the micelles themselves are not known. Interpretation of the factors which affect these parameters must therefore be carried out with caution. In addition, the inhibition of the micelle-catalyzed reactions by added electrolytes has been observed (Bunton and Robinson, 1969a Bunton et al., 1969, 1970) and, as in the cases of other anion-molecule reactions and the heterolysis of dinitrophenyl phosphate dianions, can be reasonably attributed to the exclusion of the nucleophile by the anion of the added salt. 

We have thus far considered coherent processes that take place in RPs (which in some cases been have been modulated by stochastic motion). However, the common spin-lattice and spin-spin relaxation processes familiar from magnetic resonance also come to bear on the dynamics of RPs. Typical values of Ti and T2 for small organic radicals in homogeneous solution are on the microsecond timescale and as such are rather slow relative to coherent mixing and RP diffusion. Thus, for the most part, effects of incoherent spin relaxation are not manifest in such reactions. However, for reactions in which the RP lifetime is substantially extended, for instance, by constraining the RP inside a microreactor such as a micelle (many examples in Ref. 14), relaxation effects become significant. 

The direct manifestation of this Interaction was observed a long time ago In the water concentration at which a change from monomeric aggregates to Inverse micelles took place In a H/0 mlcroemulslon (23). Adding an aromatic compound has a pronounced Influence on the water content at which mlcelllzatlon begins. 

The most reasonable explanation for the increase in apparent hydrodynamic diameter measured by DLS is the enhanced micelle-micelle interactions as the boundary of a two-phase system is approached (i.e., the pressure is lowered). Figure 4 illustrates this concept of micelle-micelle interactions, which is manifested as aggregation (or clustering) of the reverse micelle or microemulsion droplets. Since the solvent environment is essentially unchanged by this "macromolecular aggregation" (Ui) we exclude the possibility of (other than transitory) micelle-micelle coalescence to form stable, larger micelles. The micelles may coalesce briefly to form transitional species (which might be a "dumbbell" or more cylindrical structures), in which the water cores collide and intermix. 

The experimental observations show that stratification is always observed when spherical colloidal particles are present in the film at a sufficiently high volume fraction therefore, a realistic explanation can be that the stepwise transitions are manifestations of the oscillatory structural forces. The role of the hard spheres this time is played by the colloidal particles rather than by the solvent molecules. The mechanism of stratification was studied theoretically in Reference 346, where the appearance and expansion of black spots in the stratifying films were described as being a process of condensation of vacancies in a colloid crystal of ordered micelles within the film. 

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