Micellar systems, characteristic interaction

Calculating the Characteristic Interaction Parameter of the Micellar Systems Used To perform the calculation of p12 for the systems examined, i.e. Sulfonate/Genapol/ethoxylated nonylphenol mixtures, the following assumptions were made ... 

The interactions between a lipophilic or hydrophilic drug and micellar phases are caused by weak physicochemical forces such as hydrophobic (unspecific) and electrostatic effects (specific dipole-dipole, dipole-mdacoA dipole) and steric effects, whereas the hydrophobic binding to the micellar systems is dominant. An indirect indication for the presence of interactions between the micellar phase and drugs is given by molecular and dynamic parameters of the drug and the micelles (ionic mobiUty, diffusion coefficient, hydrodynamic radius, apparent molecular mass), which are altered by the solubilization of lipophilic substances in a characteristic manner. 

Numerous theories, models and mathematical approaches have been developed over the years in order to describe the micellisation process and the dependence of fundamental structural parameters of the micelles, like cmc, aggregation number (Nagg), overall size (Rm), core radius (Rc) and corona thickness (L), on the molecular characteristics of the block copolymer, with respect to the degrees of polymerisation of the constituent blocks (Na and N ), as well as the Flory-Huggins interaction parameters x between the blocks and between the blocks and the solvent. Some of these approaches use the minimisation of the total free energy of the micellar system so as to extract relations between the copolymer and micelle features, while others are based on the scaling concept of Alexander-de Gennes and... 

Regarding semianalytical mean-field theories, Noolandi and Hong [78] and Leibler et al. [79] derived the micellar characteristics by minimising the free energy of both isolated micelles and the whole micellar system. A further development was achieved by Nagarajan and Ganesh [80], who took into account the molar volumes of the solvent and blocks A and B, the interfacial tension between the B block and the solvent and the interaction parameter between the A block and the solvent. This... 

Various kinetic studies of micellar catalysis have examined the following types of micellar catalysis (1) reactions in which the micelles are reagents (2) reactions in which interactions between the micelles and the reacting species affect the kinetics and (3) reactions in which the micelles carry catalytically active substituents. Ihese studies have been undertaken to elucidate the factors that influence the rates and courses of reactions, to gain insight into the exceptional catalytic characteristics of enzymatic reactions, and to explore the usefulness of micellar systems for organic synthesis. ... 

In conventional reversed phase HPLC, differences in the physicochemical interactions of the eluate with the mobile phase and the stationary phase determine their partition coefficients and, hence, their capacity factor, k. In reversed-phase systems containing cyclodextrins in the mobile phase, eluates may form complexes based not only on hydrophobicity but on size as well, making these systems more complex. If 1 1 stoichiometry is involved, the primary association equilibrium, generally recognized to be of considerable importance in micellar chromatography, can be applied (11-13). The formation constant, Kf, of the inclusion complex is defined as the ratio of the entrance and exit rate constants between the solute and the cyclodextrin. Addition of organic modifiers, such as methanol, into the cyclodextrin aqueous mobile phase should alter the kinetic and thermodynamic characteristics of the system. This would alter the Kf values by modifying the entrance and exit rate constants which determine the quality of the separation. 

At relatively low polymer adsorption levels, oscillatory force profiles similar to those observed for micellar solutions are also seen in polyelectrolyte-containing systems. As with micellar structuring, these oscillations originate from an inhomogenous density distribution of polymer (or polymer/surfactant complexes) within the film. Furthermore, the characteristic length-scale of the oscillatory forces indicate that this structuring is controlled by electrostatic interactions. To date, no complete theory describing this phenomenon exists ... 

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