Micellar systems, solute interactions

A further possibility is the formation of liquid crystals on contact with body fluids at the site of application. The initially applied drug solution interacts with body fluids such as plasma, tears, or skin lipids and undergoes a phase transition into a mono-or multiphasic system of liquid crystals (Fig. 15). For example, oily solutions of reverse micellar solutions of phospholipids, which solubilize additional drug, trans-... 

The influence of the addition of cetyl trimethyl ammonium chloride, CTAC, to the reverse micellar solution affects the droplet size and micellar interactions, as demonstrated by the DQLS experiment (64). Addition of CTAC to micellar system at a given water content leaves the droplet size unchanged, whereas a decrease in the intermicellar attraction has been observed. This decrease is more important for high CTAC concentrations. This has been interpreted to steric repulsion induced by the long hydrocarbon tail of CTAC (C ft). Thus, the addition of this compound to CdS synthesis could modify the nucleation and/or growth process. The experiments were performed by solulization of CTAC in the micellar solution containing either sodium sulfide or Cd(AOT)2. 

Clearly, the infrared spectra of the sodium and potassium decanoate micellar solutions are considerably different, as are their pressure dependencies. Since the only difference between these two micellar systems is the size, and thus the charge density of the counterions, the different infrared spectra must be taken as evidence that in the alkali decanoate micelles the sodium or potassium counter cations interact differently with the carboxylate groups of the surfactant molecules. 

Hoffmann, H. (2000) The micellar structures and macroscopic properties of surfactant solutions. In H. Hoffmann, M. Schwoerer and Th. Vogtmann (eds). Macromolecular Systems Microscopic Interactions and Macroscopic Properties. Wiley-VCH, pp 199-250. 

Tables VI and VII present some representative data on the binding constants and partition coefficients reported for the interaction of selected solutes with different surfactant micellar systems. The strength of the association of solutes with surfactant micelle assemblies is dictated by the net electrostatic, hydrogen-bonding, and/or hydrophobic interactions possible for a given solute - micelle combination under the prevailing experimental conditions.

There continues to be extensive interest in latexes and micellar systems. The structure of acrylic latex particles has been investigated by non-radiative energy transfer by labelling the co-monomers with fluorescent acceptor-donor systems. Phase separations could also be measured in this way. Excimer fluorescence has been used to measure the critical micelle temperature in diblock copolymers of polystyrene with ethylene-propylene and the results agree well with dynamic light scattering measurements. Fluorescence anisotropy has been used to measure adsorption isotherms of labelled polymers to silica as well as segmental relaxation processes in solutions of acrylic polymers. In the latter case unusual interactions were indicated between the polymers and chlorinated hydrocarbon solvents. Fluorescence analysis of hydrophobically modifled cellulose have shown the operation of slow dynamic processes while fluorescence... 

Partial molar volumes and compressibilities of solutes at infinite dilution have proved valuable as a tool for studying water-solute interactions in aqueous solution, and a number of systems have been investigated. It has therefore been of interest to determine these quantities for solubilizates in the micellar state. By using Equation 6.23 these quantities can be obtained. 

Reversed micellar systems have certain attributes which can be exploited when considering enzymatically-based synthesis reactions. These systems can solubilize hydrophilic and hydrophobic reactants and, If the reactants Interact with the surfactant layer, higher concentrations can be obtained than Is possible In either an aqueous or an organic environment. Partitioning of reactants between the bulk organic portion of a reversed micellar solution and the micellar core can result In localized high concentrations of polar reactants. This can be used to promote desired reactions, such as the synthesis of dlpeptldes. 

Micellar media are formed from tensioactive molecules in aqueous solution. Mi-cellization is a manifestation of the strong self-association of water and water-like solvents [95]. Micelles are known to increase the solubilization of weakly polar substances in water and, as a consequence, their presence determines the magnitude of hydrophobic interactions. Micelles aggregate spontaneously in aqueous solution beyond a critical concentration which is a function of pressure [96]. As a result, pressure may induce an extra kinetic effect on the rate of organic reactions carried out in aqueous micellar systems. Representative ionic micelles are sodium dodecyl sulfate (SDS) and tetradecyltrimethylammonium bromide (TTAB). Recent examples demonstrate the beneficial effect of the presence of surfactants in Lewis acid-catalyzed reactions, a kind of biactivation [97]. 

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