Micelle forming surfactant

These effects can be calculated to some extent, where Cw depends not only on K%/ but also on surfactant concentration. Initially it is assumed that the surfactant micelles form part of the aqueous phase. 

The AH , term results from the part of the binding process in which the Na+ ions, electrostatically bound to the polyion (atmospheric binding), are replaced by the monovalent surfactant cations. This contribution is assumed to be small in comparison with the other two and can be neglected. When the surfactant micelles form in the presence of a hydrophilic polyelectrolyte, the third contribution, AH in Eq. 4 may be assumed to be much smaller than the second term, since only pine electrostatic interactions are expected to act between hydrophilic polyion and ionic micelle. However, the AH, term in the case of interaction between a hydrophobic polyelectrolyte and surfactant micelle may not be neglected. To confirm this, it is instructive to... 

Figure 9 The spot of lower thickness in a stratifying liquid film corresponds to a local decrease in the number of micelle layers in the col-loid-ciystal-like stmeture of surfactant micelles formed inside the liquid film. The appearance of spots coidd be attributed to the condensation of vacancies in that stmeture. (From Ref. 82.)...

When all the micelles are gone, no additional polymer particles are formed, so the rate of polymerization slows. The surface tension rises as the aqueous phase is no longer saturated with surfactant. As the particles are washed out of the reactor, the extent of conversion decreases. With the total surface area decreasing and new surfactant flowing in, the surface tension decreases. When the aqueous phase becomes saturated with surfactant, micelles form, they adsorb free radicals, and polymerization can commence in them. The process begins anew. 

The formation of these DNA gel particles constitutes an example of strong associative phase separation. An indication of the strength of this interaction is the formation of a stronger film (or skin) constituted by the polyelectrolyte-surfactant complex. Preliminary results of S AXS measurements have supported the existence of an ordered structure formed on the hydrated skin of the obtained particles. SEM images of the cross-section of the particles have given evidence for the existence of a shell structure, its formation being more pronounced in the case of ss-DNA. The capsule shells obtained may be considered as physical networks in which surfactant micelles form polycationic-multianionic electrostatic complexes as crosslink points. 

The energetics and kinetics of film formation appear to be especially important when two or more solutes are present, since now the matter of monolayer penetration or complex formation enters the picture (see Section IV-7). Schul-man and co-workers [77, 78], in particular, noted that especially stable emulsions result when the adsorbed film of surfactant material forms strong penetration complexes with a species present in the oil phase. The stabilizing effect of such mixed films may lie in their slow desorption or elevated viscosity. The dynamic effects of surfactant transport have been investigated by Shah and coworkers [22] who show the correlation between micellar lifetime and droplet size. More stable micelles are unable to rapidly transport surfactant from the bulk to the surface, and hence they support emulsions containing larger droplets. 

In some cases, dye-forming moieties attached to a polymeric backbone, called a polymeric coupler, can replace the monomeric coupler in coupler solvent (51). In other reports, very small particles of coupler solubilized by surfactant micelles can be formed through a catastrophic precipitation process (58). Both approaches can eliminate the need for mechanical manipulation of the coupler phase. 

Liquid Crystal Third Phase. In addition to micelles and microemulsion droplets, surfactants may form Hquid crystals. A Hquid crystal is a separate phase, which comes out of solution, not like the micelles or microemulsion droplets, which are microscopic entities within the solution. 

Suspension polymerization produces beads of plastic for styrene, methyl methacrviaie. viny l chloride, and vinyl acetate production. The monomer, in which the catalyst must be soluble, is maintained in droplet fonn suspended in water by agitation in the presence of a stabilizer such as gelatin each droplet of monomer undergoes bulk polymerization. In emulsion polymerization, ihe monomer is dispersed in water by means of a surfactant to form tiny particles held in suspension I micellcsK The monomer enters the hydrocarbon part of the micelles for polymerization by a... 

FIG. 1 Self-assembled structures in amphiphilic systems micellar structures (a) and (b) exist in aqueous solution as well as in ternary oil/water/amphiphile mixtures. In the latter case, they are swollen by the oil on the hydrophobic (tail) side. Monolayers (c) separate water from oil domains in ternary systems. Lipids in water tend to form bilayers (d) rather than micelles, since their hydrophobic block (two chains) is so compact and bulky, compared to the head group, that they cannot easily pack into a sphere [4]. At small concentrations, bilayers often close up to form vesicles (e). Some surfactants also form cyhndrical (wormlike) micelles (not shown). 

The size and shape of micelles also are affected by fluormation Whereas hydrocarbon surfactants usually form spbencal micelles, linear fluorocarbon surfactants tend to produce larger rodhke speacs [31, 32 This is attnbuted to two inherent charac-tenshcs of the (CF2) chain (1) it adopts a hehcal rather than a linear zigzag conformation [dd 34, 35, 36], and (2) it is much suffer than the (CH2) cham [d5 37, 38] The relatively sbff, helical (CFj) chains thus prefer cylindrical to sphencal packing... 

A macroporous polystyrene-divinylbenzene copolymer is produced by a suspension polymerization of a mixture of monomers in the presence of water as a precipitant. This is substantially immiscible with the monomer mixture but is solubilized with a monomer mixture by micelle-forming mechanisms in the presence of the surfactant sodium bis(2-ethylhexylsulfosuccinate) (22). The porosity of percentage void volume of macroporous resin particles is related to percentage weight of the composite (50% precipitant, 50% solvent) in the monomer mixture. 

In the latter function, the reagent behaves as a surfactant and forms a cationic micelle at a concentration above the critical micelle concentration (1 x 10 4M for CTMB). The complexation reactions occurring on the surface of the micelles differ from those in simple aqueous solution and result in the formation of a complex of higher ligand to metal ratio than in the simple aqueous system this effect is usually accompanied by a substantial increase in molar absorptivity of the metal complex. 

Functionalized polyelectrolytes are promising candidates for photoinduced ET reaction systems. In recent years, much attention has been focused on modifying the photophysical and photochemical processes by use of polyelectrolyte systems, because dramatic effects are often brought about by the interfacial electrostatic potential and/or the existence of microphase structures in such systems [10, 11], A characteristic feature of polymers as reaction media, in general, lies in the potential that they make a wider variety of molecular designs possible than the conventional organized molecular assemblies such as surfactant micelles and vesicles. From a practical point of view, polymer systems have a potential advantage in that polymers per se can form film and may be assembled into a variety of devices and systems with ease. 

The frequent breaking and reforming of the labile intermolecular interactions stabilizing the reversed micelles maintain in thermodynamic equilibrium a more or less wide spectrum of aggregates differing in size and/or shape whose relative populations are controlled by some internal (nature and shape of the polar group and of the apolar molecular moiety of the amphiphile, nature of the apolar solvent) and external parameters (concentration of the amphiphile, temperature, pressure) [11], The tendency of the surfactants to form reversed micelles is, obviously, more pronounced in less polar solvents. 

Below some critical surfactant concentration, the system is two-phase with excess oil or water depending on the oil/water concentration. On adding more surfactant, the system moves into a one-phase region with normal micelles forming in water-rich systems. The water constitutes the continuous phase, solvating the headgroups of the surfactant whose hydro-phobic tails solubilise oil in the core of the micelle. In oil rich systems, reverse-micelles form. With further increases in surfactant composition. 

Templates made of surfactants are very effective in order to control the size, shape, and polydispersity of nanosized metal particles. Surfactant micelles may enclose metal ions to form amphiphilic microreactors (Figure 11a). Water-in-oil reverse micelles (Figure 11b) or larger vesicles may function in similar ways. On the addition of reducing agents such as hydrazine nanosized metal particles are formed. The size and the shape of the products are pre-imprinted by the constrained environment in which they are grown. 

In the past few years, a range of solvation dynamics experiments have been demonstrated for reverse micellar systems. Reverse micelles form when a polar solvent is sequestered by surfactant molecules in a continuous nonpolar solvent. The interaction of the surfactant polar headgroups with the polar solvent can result in the formation of a well-defined solvent pool. Many different kinds of surfactants have been used to form reverse micelles. However, the structure and dynamics of reverse micelles created with Aerosol-OT (AOT) have been most frequently studied. AOT reverse micelles are monodisperse, spherical water droplets [32]. The micellar size is directly related to the water volume-to-surfactant surface area ratio defined as the molar ratio of water to AOT,... 

In addition, water motion has been investigated in reverse micelles formed with the nonionic surfactants Triton X-100 and Brij-30 by Pant and Levinger [41]. As in the AOT reverse micelles, the water motion is substantially reduced in the nonionic reverse micelles as compared to bulk water dynamics with three solvation components observed. These three relaxation times are attributed to bulklike water, bound water, and strongly bound water motion. Interestingly, the overall solvation dynamics of water inside Triton X-100 reverse micelles is slower than the dynamics inside the Brij-30 or AOT reverse micelles, while the water motion inside the Brij-30 reverse micelles is relatively faster than AOT reverse micelles. This work also investigated the solvation dynamics of liquid tri(ethylene glycol) monoethyl ether (TGE) with different concentrations of water. Three relaxation time scales were also observed with subpicosecond, picosecond, and subnanosecond time constants. These time components were attributed to the damped solvent motion, seg-... 

The situation is similar to the exchange between the monomer and the micellar states. Usually, the exchange between the monomer and the micellar states is fast. The spectra at surfactant concentrations above CMC, therefore, consist of a single set of peaks whose chemical shifts are averaged between the monomer and micellar states. Such an example is shown by spherical micelles formed by lithium perfluoro-octylsulfonate (FOS )... 

Disperse systems can also be classified on the basis of their aggregation behavior as molecular or micellar (association) systems. Molecular dispersions are composed of single macromolecules distributed uniformly within the medium, e.g., protein and polymer solutions. In micellar systems, the units of the dispersed phase consist of several molecules, which arrange themselves to form aggregates, such as surfactant micelles in aqueous solutions. 

The method for creating acceptor sink condition discussed so far is based on the use of a surfactant solution. In such solutions, anionic micelles act to accelerate the transport of lipophilic molecules. We also explored the use of other sink-forming reagents, including serum proteins and uncharged cyclodextrins. Table 7.20 compares the sink effect of 100 mM (5-cyclodextrin added to the pH 7.4 buffer in the acceptor wells to that of the anionic surfactant. Cyclodextrin creates a weaker sink for the cationic bases, compared to the anionic surfactant. The electrostatic binding force between charged lipophilic bases and the anionic surfactant micelles... 

In suspension polymerization, the monomer is agitated in a solvent to form droplets, and then stabilized through the use of surfactants to form micelles. The added initiator is soluble in the solvent such that the reaction is initiated at the skin of the micelle. Polymerization starts at the interface and proceeds towards the center of the droplet. Polystyrene and polyvinyl chloride are often produced via suspension polymerization processes. 

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