Mixed micelles constituents

Materials and Polymerization. Styrene and methyl methacrylate were obtained from commercial sources and were distilled to remove inhibitor. After distillation, the monomers were stored, under nitrogen, in a refrigerator. For the mixed emulsifier system, Emulphogene BC840(GAF), tridecyloxy-polyethylene-oxyethanol, was used as the nonionic constituent, and sodium lauryl sulfate (K and K Labs) was used as the ionic constituent. The sodium lauryl sulfate was at a concentration below its cms whereas the BD-840 was at a concentration above its cmc. This emulsifier system has been shown to yield mixed micelles (2)/ having a low ionic change (2)/ which produce latlces with rather narrow particle size distributions (2 ) ... 

Within a broad range of concentrations above the CMC the surfactant molecules are associated into spherical micelles, the so-called Hartley -Rehbinder micelles. The hydrocarbon core of such micelles remains liquid, even though its state is different from that of the corresponding bulk hydrocarbon, such as in the emulsion droplets. The formation of mixed micelles containing different additives (even when the constituent molecules substantially differ in size), as well as the dissolution of liquid hydrocarbons (otherwise insoluble in water) in hydrophobic cores (solubilization, see Chapter VI, 4) points to a liquid-like state of micellar hydrocarbon cores. 

Riemersma [192] suggests that phosphate groups belonging to phosphoino-sitides, phosphatidic acid and other anionic lipids were involved in the ionic interaction of the surfactant head groups while the alkyl chain actually penetrated the membrane bilayer. At a certain concentration the membrane would form mixed micelles with the surfactant cations leading to higher permeability and cytolysis. However, both anionic and cationic surfactants induce lysis and their mode of action cannot be identical. Bradford et al. [194] examining the solubilization of microsomal constituents observed that both CTAB and... 

Exchange of unimers between two different types of block copolymer micelles has often been referred to as hybridization. This situation is more complex than for the case described above because thermodynamic parameters now come into play in addition to the kinetic ones. A typical example of such hybridization is related to the mixing of micelles formed by two different copolymers of the same chemical nature but with different composition and/or length for the constituent blocks. Tuzar et al. [41] studied the mixing of PS-PMAA micelles with different sizes in water-dioxane mixtures by sedimentation velocity measurements. These authors concluded that the different chains were mixing with time, the driving force being to reach the maximum entropy. 

The maximum additive concentration (MAC) is defined as the maximum amount of solubilisate, at a given concentration of surfactant, that produces a clear solution. Different amounts of solubilisates, in ascending order, are added to a series of vials containing the known concentration of surfactant and mixed until equilibrium is reached. The maximum concentration of solubilisate that forms a clear solution is then determined visually. This same procedure can be repeated for the different concentrations of surfactant in a known amount of solubilisate in order to determine the optimum concentration of surfactant (Figure 4.24). Based on this information, one can construct a ternary phase diagram that describes the effects of three constituents (i.e., solubilisate, surfactant, and water) on the micelle system. Note that unwanted phase transitions can be avoided by ignoring the formulation compositions near the boundary. In general, the MAC increases with an increase in temperature. This may be due to the combination of the increase of solubilisate solubility in the aqueous phase and the micellar phase rather than an increased solubilization by the micelles alone. 

Discussion of Thermodynamic Behavior of the Ionic Constituents of Micelles in Mixed Solvents... 

Microporous zincophosphate crystals of zeolitic structure have been synthesized by Dutta and colleagues [335, 222] via multiple microemulsions. In the first investigation [335], these authors used two reverse microemulsions, based on the system AOT/n-hexane, containing (a) aqueous solution of Zn(N03)2.6H20 and (b) aqueous solution with H3PO4 and tetramethylammonium hydroxide (the latter was required for incorporation of the phosphate in the reverse micelle). For the Zn-micelle, the [AOT]/[H20] ratio was 13, while for the phosphate-micelle, the value went up to 21. Uptake of the constituents in the micelles was examined by chemical analysis. The two microemulsions were finally mixed at room temperature. Particles grew from 14 nm to - 150 nm in three days, and then became stable at --140 nm. 

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