Nonionic reverse micelles

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 synthesis of Si02 particles by ammonia-catalyzed hydrolysis of TEOS has been also carried out in Aerosol OT reversed micelle systems. The particles precipitated in this systems are spheres, but they have generally a broad size distribution comparing with that of nonionic reversed micelles compared to the normalized standard deviation of <10% in polyoxyethylene(5) nonylphenyl ether, that in Aero-... 

Unlike TEOS hydrolysis, Si02 particles have been also prepared by hydrolysis of Na2Si02 and Na4Si02 in nonionic reversed micelle systems. Spherical and poly-disperse particles of 31.8 nm mean diameter were produced in polyoxyethylene(9.5) octylphenyl ether-hexanol-cyclohexane systems (25), but more uniform and dense particles were precipitated by hydrochloric acid-catalyzed hydrolysis in a mixture of polyoxyethylene(5) nonylphenyl ether and polyoxyethylene(9) nonylphenyl ether in cyclohexane systems at pH 11 (26). The uniform particle formation at higher pH is attributed to the charge repulsion by OH- adsorbed on particle surface. The particles of specific surface area of 347 m2 g-1 can be obtained by calcination of particles produced at pH 2. 

In particle formation in ionic and nonionic reversed micelles as mentioned earlier, simple electrolytes such as AgN03 and NaCl were used as reactants. If the... 

McFann GJ, Johnston KP, Flowdle SM. Solubilization in nonionic reverse micelles in carbon dioxide. AIChE J 1994 40 543-555. 

Kawai T, Fujino A, Kon-No K. Synthesis of monodisperse Zr02 particles in polyoxy-ethylated nonionic reversed micelles. Colloid Surf A 1996 109 245-53. 

Dutt, G. B. 2004. Rotational relaxation of hydrophobic probes in nonionic reverse micelles Influence of water content on the location and mobility of the probe molecules. J. Phys. Chem. B 108, 805-810. 

In addition to AOT-based microemulsions, a nonionic reverse micelle (GGDE/TX-100), containing a functional nonionic surfactant N-gluconyl glutamic acid didecyl ester (GGDE) and Triton X-100 (TX-lOO), was evaluated as a good alternative in which YADH exhibits higher catalytic activity and stability [89]. 

Ruckenstein, E. and Karpe, P. (1991) Enzymatic super- and subactivity in nonionic reverse micelles. /. Phys. 

The fluorescence polarization technique is a very powerful tool for studying the fluidity and orientational order of organized assemblies aqueous micelles, reverse micelles and microemulsions, lipid bilayers, synthetic nonionic vesicles, liquid crystals. This technique is also very useful for probing the segmental mobility of polymers and antibody molecules. 

Nazario LMM, Hatton TA, Crespo JPSG (1996) Nonionic cosurfactants in AOT reversed micelles Effect on percolation, size, and solubilization site. Langmuir... 

Microemulsions are dynamic systems in which droplets continually collide, coalesce, and reform in the nanosecond to millisecond time scale. These droplet interactions result in a continuous exchange of solubilizates. The composition of the microemulsion phase determines the exchange rate through its effect on the elasticity of the surfactant film surrounding the aqueous microdomains. Compared with nonionic surfactant-based microemulsions, AOT reverse micelles have a more rigid... 

With nonionic PEO emulsifiers, intermolecular interactions vary with temperature and types of metal ions and solvents. At low temperatures, nonionic emulsifiers are hydrophilic and form normal micelles. At higher temperatures they are lipophilic and form reverse micelles. A weak interaction with metal ions favors the stability of associates against moisture. On the other hand, a strong interaction may lead to a completely amorphous system. Ethanol as a co-solvent is a moderate solvent for PEO at low temperatures, but its power improves as the temperature is raised [34]. This means that solutions of the PEO copolymers in water and ethanol have opposing temperature coefficients of solubility negative for water and positive for ethanol. 

Surfactants are classified on the basis of the charge carried by the polar headgroup as anionic, cationic, nonionic, and amphoteric. Surfactant headgroups are dipoles, especially ionic ones that exist as ion pairs in hydrocarbon solvents. Electrostatic dipole-dipole attraction between headgroups in hydrocarbon solvents is the driving force for the formation of reverse micelles, or micellar aggregates, see Fig. 3.1 and Fig. 3.2. 

Most systems examined to date have employed the AOT anionic reversed micellar system (366-370). In one case, amylase was extracted using trioctylmethylammonium chloride (cationic surfactant) in isooctane (375) while in another, catalase was extracted using a cationic DTAB/octane/hexanol reversed micelle (377). In our own research, we have successfully employed nonionic Igepal CO-530 -CCl, cationic CTAB - hexanol, and zwitterionic lecithin - CC1, reversed micellar systems in the extraction of some amino acids and proteins (379). The availability of such a pool of different charge-type micellar systems allows one flexibility in the development of such extraction schemes. In fact, preliminary results seem to indicate that better extractions are obtainable in some instances via use of zwitterionic reversed micellar media (379). 

The spectroscopic probe pyridine-N-oxide was used to characterize polar microdomains in reverse micelles in supercritical ethane from 50 to 300 bar. For both anionic and nonionic surfactants, the polarities of these microdomains were adjusted continuously over a wide range using modest pressure changes. The solubilization of water in the micelles increases significantly with the addition of the cosolvent octane or the co-surfactant octanol. Quantitative solubilities are reported for the first time for hydrophiles in reverse micelles in supercritical fluids. The amino acid tryptophan has been solubilized in ethane at the 0.1 wt.% level with the use of an anionic surfactant, sodium di-2-ethylhexyl sulfosuccinate (AOT). The existence of polar microdomains in aggregates in supercritical fluids at relatively low pressures, along with the adjustability of these domains with pressure, presents new possibilities for separation and reaction processes involving hydrophilic substances. 

Figure 8. Variable polarities of microdomains in reverse micelles of nonionic surfactant (0.01 M Shell C11-14 EO5) in ethane (T = 35 C)...

Highly polar microdomains exist in reverse micelles of AOT and nonionic polyethylene oxide surfactants in ethane, even below 100 bar, both with and without cosolvents. Without cosolvents these domains are likely very small since values of Wo are small. The addition of the cosolvent octane provides a means to take up large amounts of water over a wide pressure range. The polarities in the interior of the micelles approach that of bulk water. The existence of polar microdomains in supercritical fluids at relatively low pressures presents an opportunity for new separation and reaction processes involving hydrophilic substances. 

In this article we describe the phase behavior of a microemulsion system chosen for the free radical polymerization of acrylamide within near-critical and supercritical alkane continuous phases. The effects of pressure, temperature, and composition on the phase behavior all influence the choice of operating parameters for the polymerization. These results not only provide a basis for subsequent polymerization studies, but also provide data on the properties of reverse micelles formed in supercritical fluids from nonionic surfactants. 

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