Properties within reversed micelles

Generation of nanoparticles under Langmuir monolayers and within LB films arose from earlier efforts to form nanoparticles within reverse micelles, microemulsions, and vesicles [89]. Semiconductor nanoparticles formed in surfactant media have been explored as photocatalytic systems [90]. One motivation for placing nanoparticles within the organic matrix of a LB film is to construct a superlattice of nanoparticles such that the optical properties of the nanoparticles associated with quantum confinement are preserved. If mono-layers of capped nanoparticles are transferred, a nanoparticle superlattice can be con-... 

Effective pH values in soft-core RMs. Characterization of the acidity in the aqueous soft-core is important as ionizable compounds are solubilized in the water pool. The micellar core has a very high degree of organization of water. The water pool within reverse micelles is a different solvent than bulk water. The most interesting range of water content corresponds to rather small water pools (water-to-surfactant ratio of 3 to 10) in which peculiar properties of water cause the largest changes in behavior as compared to their behavior in bulk water. A water to surfactant ratio of 1 1 represents a very small, almost undetectable, quantity of... 

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. 

Dynamic light-scattering experiments or the analysis of some physicochemical properties have shown that finite amounts of formamide, A-methylformamide, AA-dimethyl-formamide, ethylene glycol, glycerol, acetonitrile, methanol, and 1,2 propanediol can be entrapped within the micellar core of AOT-reversed micelles [33-36], The encapsulation of formamide and A-methylformamide nanoclusters in AOT-reversed micelles involves a significant breakage of the H-bond network characterizing their structure in the pure state. Moreover, from solvation dynamics measurements it was deduced that the intramicellar formamide is nearly completely immobilized [34,35],... 

The determination of the enzyme activity as a function of the composition of the reaction medium is very important in order to find the optimal reaction conditions of an enzyme catalysed synthesis. In case of lipases, the hydrolysis of p-nitrophenyl esters in w/o-microemulsions is often used as a model reaction [19, 20]. The auto-hydrolysis of these esters in w/o-microemulsions is negligible. Because of the microstructure of the reaction media itself and the changing solvent properties of the water within the reverse micelles, the absorbance maximum of the p-nitrophenol varies in the microemulsion from that in bulk water, a fact that has to be considered [82]. Because of this, the water- and surfactant concentrations of the applied micro emulsions have to be well adjusted. 

The hyperactivity of, for example, lipases at low w -values (shown in Fig. 5) is explained by the water-shell-model [2]. The activity of the enzyme at w -values higher than 5 corresponds to its activity in bulk aqueous solutions. There exist two aqueous regions within a reverse micelle, schematically shown in Fig. 6. One is located in the inner part of the reverse micelle and has the same physical properties as bulk water the other is attached to the polar head groups of the surfactant and differs in its physical properties strongly from bulk water. 

Experimental results suggest that hydrophillic proteins tend to be solubilized within the water core of the reversed micelles, while lipophilic biomolecules can either stay in the interface or even partially exposed to the organic phase.45 Because of the protection offered by the reversed micelles, proteins were shown to maintain their functional properties.47 The retention of bioactivity depends strongly on the solvent system and it is usually not 100%.45... 

These observations beg the question why do the hydrophobic solutes favour the polar cores of the reversed micelles more than do the polar amino acids This effect would seem to be due to the unusual properties of the water within the reversed micelles, which is known to be more structured than water in the bulk aqueous phase... 

Another immobilization technique proposed is nanoentrapment into NPs. In this method, a water-in-oil microemulsion system is used for the fabrication of NPs and for the dispersion of enzyme. This procedure leads to the creation of discrete NPs through polymerization in the water phase or on the interface, in which the enzyme is dispersed [195, 196], One of the challenges of this approach is the difficulty in controlling the size of reverse micelles, as well as the number of enzyme molecules within each reverse micelle, which will directly affect the final properties of enzyme-entrapped nanoparticles [6],... 

Water inside a carbon nanotube (CNT) shows another set of unusual features which have been the subjects ofgreat interest in recent years and are currently being studied extensively by experiments and simulations. A remarkable aspect unearthed is the ability of a CNT to act as water transporter and filter. The properties of water inside a CNT depend on the diameter d of the CNT, which is analogous to the parameter Wq of reverse micelles discussed in the preceding chapter. However, water within a single-wall CNT shows unusual features, such as single-file diffusion, the theory of which was developed in the past but a proper model system was lacking. The orientational motion of individual water molecules exhibits slow dynamics, quite different from those in the bulk. 

The first supramolecular self-reproduction experiments involved reverse micelles. Bachman et aL (22) have demonstrated that a reverse micellar system or water-in-oil microemulsion is endowed with the property of self-reproduction. The starting point is a microemulsion stabilized by octanol and octanoic acid. To this system, the fatty acid ester octyl octanoate was added. This is hydrolysed by LiOH to give the fatty acid and alcohol. As the reaction proceeds, more droplets of a similar structure/composition to those present initially are produced. This is because the reaction is localized within the boundary of the structure and so the reaction leads to the production of components of the boundary. 

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