Micelle ionic, with solvent composition

Figure 2. Variation of the degree of dissociation of ionic micelles with solvent composition. ( ), Data from emf measurements, (O, O), conductance 4 mobility measurements. D = decyl, DO = dodecyl.

Figure 6. Variation of the apparent charge of the ionic micelles with solvent composition Zmic = an...

The popularity of reversed-phase liquid chromatography (RPC) is easily explained by its unmatched simplicity, versatility and scope [15,22,50,52,71,149,288-290]. Neutral and ionic solutes can be separated simultaneously and the rapid equilibration of the stationary phase with changes in mobile phase composition allows gradient elution techniques to be used routinely. Secondary chemical equilibria, such as ion suppression, ion-pair formation, metal complexatlon, and micelle formation are easily exploited in RPC to optimize separation selectivity and to augment changes availaple from varying the mobile phase solvent composition. Retention in RPC, at least in the accepted ideal sense, occurs by non-specific hydrophobic interactions of the solute with the... 

Nonspherical aggregates (cylindrical micelles, vesicles, lamellae, etc.) were detected experimentally for a number of non-ionic block copolymers (see, e.g., [50, 136-139]) and copolymers with weakly dissociating PE block [102, 140]. Morphological transformations in non-ionic PI-fetocA -PS micelles were triggered by variations in molecular weight of the PS block [50] or by variations in the solvent composition [137, 138]. The latter studies clearly indicate the possibility of stimuli-responsive transitions (sphere —> cylinder —> vesicle) for non-ionic block copolymer aggregates in mixed organic solvents. It was also demonstrated [58] that... 

Several high-performance liquid chromatography (HPLC) separation techniques have been used in combination with different detection methods to characterize poly(ethylene glycol)s and their amphiphilic derivatives. SEC is a particularly attractive analytical tool for the investigation of non-ionic surfactants because it can provide information for their composition, molecular weight, and molecular-weight distribution along with their micellization in selective solvents. This entry wiU survey briefly both applications with major emphasis on the choice of the most appropriate eluent and stationary phase. 

For block copolymers comprising ionic hydrophilic blocks one has, in addition to the parameters discussed in the previous section, several new parameters that influence the micelle characteristics. Here, we focus on how these new parameters, i.e., the charge density in the corona and the ionic strength influence the micelle characteristics. In this section we therefore focus on a given molecular composition and we opt for a symmetric case, 200 200, and fixed the values for the excluded-volume interactions parameters xbs = XNaB = Xcib = Ztb = 1 -5 and Xas = Xnos = Xcis = 0. Hence, we choose for the scenario that the ions have similar excluded-volume interactions with the polymer segments as the solvent. Note that in practice ions might have some specific affinity for either the core or the coronal blocks, and this situation could be also addressed in frames of the SF-SCF model. 

The catalytic behavior and the stability of enzymes in reverse micelles are highly dependent on the composition and the structure of the micioanulsion. The activity of entrapped enzymes strongly depends on the water content, the nature of the organic solvent, as well as the nature and the concentration of surfactant. Various surfactants, including the anionic AOT, the cationic CTAB, nonionics such as Triton, Brij, ethoxylated fatty alcohols, and zwitterionic phospholipids (phosphatidylcholine), were used for the preparation of reverse miceUar systems-containing enzymes (Table 13.1). Most inveshgated systans used AOT as the surfactant because its phase behavior is well understood. The activity of some enzymes has been reported to depend on the surfactant concentration and in some cases it was attributed to the interaction of the enzymes with the miceUar membrane [8,26,27]. Recent developments in this area inclnde the use of modified surfactants or their mixtures with other additives and cosurfactants such as alcohols and sugars or the use of aprotic solvents for the reduction of the ionic interactions between the enzyme molecules and the micellar interface in order to improve the enzyme catalytic behavior and operational stabihty [8,17,28-34]. 

Fig. 1 Schematic representation of co-assembly of two oppositely charged ionic-neutral diblock copolymers in water into complex coacervate core micelles, in short C3Ms, with a core comprising the oppositely charged monomers surrounded by a shell of neutral, water-soluble monomers. The two monomer types in the corona may mix left) or segregate radially (mid-left), laterally (mid-right) or both radially and laterally (right) depending on the chemical composition of the block copolymers and hence the miscibility and differential solvent quality of the neutral monomers. This may lead to the formation of onion-like micelles, also known as core-shell-corona structures (mid-left), Janus micelles (mid-right) or patchy micelles, also known as raspberry-like micelles (right). Figure from Ref. [188]...

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