Reverse micelles, emulsion process

Fluorescent silica nanoparticles, called FloDots, were created by Yao et al. (2006) by two synthetic routes. Hydrophilic particles were produced using a reverse micro-emulsion process, wherein detergent micelles formed in a water-in-oil system form discrete nanodroplets in which the silica particles are formed. The addition of water-soluble fluorescent dyes resulted in the entrapment of dye molecules in the silica nanoparticle. In an alternative method, dye molecules were entrapped in silica using the Stober process, which typically results in hydrophobic particles. Either process resulted in luminescent particles that then can be surface modified with... 

Figure 14.23 Silica nanoparticles containing fluorescent dye molecules can be prepared using a reverse micelle suspension process (a) The water-in-oil emulsion is formed with the aqueous phase droplets containing TEOS and dye molecules in detergent, (b) The final particles contain entrapped dye within the silica particle matrix, creating highly fluorescent particles.

Other claimed matter DBT for enrichment, biocatalyst preparation contacting process Enzymes contacting process Pure compounds as feedstock Membrane fragments and extracts Cell-free extract (envelope and its fragments + associated enzyme) reversible emulsion microemulsion reverse micelles Cell-free enzyme preparation microemulsified process RR and derivatives and other biocatalyst concepts + any known microorganism active for C—S bond cleavage... 

An alternative to the injection method for importing enzymes into a microemulsion is the phase transfer method. In this method, a layer of an aqueous enzyme solution is located under a mixture of surfactant and oil. Upon gentle shaking, the enzyme is transferred into the reverse micelles of the hydrocarbon phase. Finally, the excess of water is removed and the hydrophobic substrates can be added. The main advantage of this method is that it ensures thermodynamically stable micro emulsions with maximum water concentrations. However, the method is very time consuming. The method is often applied in order to purify, concentrate or renaturate enzymes in the reverse micellar extraction process [54-58]. 

In many of the examples presented in Table XIV, the existence of reversed micelles (331,231,231,211,231,HI,221,or micro-emulsions (349-352) is implicated and their presence is an important factor which influences the characteristics of a particular extraction process. Often, quantitative descriptions of such extractions is difficult due to the fact that many of the reversed micellar systems formed undergo an indefinite type of self-association in... 

Multiple emulsions are the basis of so-called liquid membrane separation processes, where one solute is prefermtially transferred from, say, the outer to the inner aqueous phase of a water-in-oil-in-watCT emulsion. The preferred solute is transferred faster because it is more soluble in the oil phase than other species dissolved in the inner aqueous phase. Transport across the oil phase may occur by diffusion of solute molecules or solute-containing reverse micelles or microemulsion drops. Sometimes a carrier is added to the oil to increase solute solubility in the oil by formation of a solute/carrier complex. 

Other new processes have involved modifications of the solvent evaporation method. To produce a more homogeneous emulsion and stabilize the protein, surfactants have been added to the protein phase. For example, researchers have claimed that the addition of hydrophobic ion pairs to the protein phase allows a more homogeneous mixture of the protein in the polymer phase and provides stabilization of the protein (M. C. Manning, personal communication, 1994). Reversed micelles (sucrose esters of fatty acids) stabilize ultrafine emulsions of the protein in the polymer phase and provide stabilization ofthe protein (Hayashi et al, 1994). In addition, the use of a multiphase encapsulation system may protect the protein from denaturation. One t q)e of multiphase system involves the suspension of... 

The emulsion process can be used to synthesize inorganic and metallic nanoparticles with controlled particle size and morphology [99, lOOj. An emulsion is defined as a colloidal suspension of a hquid within another liquid. Emulsions can be divided into two categories (i) oil-in-water, where the oil droplets are suspended homogeneously in water (the droplets are referred to as micelles) and (ii) water-in-oil, where water droplets are suspended homogeneously in oil, known as reverse micelles. 

In the framework of this research topic, PPy chains self-assembled in nanowires with a coral-like shape can be obtained by FeCb induced oxidative polymerization and dodecil-benzenic sulphonic acid (DBSA) dopant [106] oxidative polymerization is a widely used method for the attainment of polymeric nanostructures. For example, bundles of self-assembled PPy nanotubes have been fabricated by polymerization reaction with bis(2-ethylhexyl) sulfosuccinate reverse (water-in-oil) emulsions [107] and rods with enhanced electrical conductivity and thermal stability are reported to be formed via a self-assembly process of micelle obtained from a oxidative polymerization in the presence of p-toluensulfonic acid used as surfactant and doping agent [108, 109]. A further example of PPy nanotubes synthesized by oxidative polymerization in octane is reported in Fig. 1.7 [107]. 

Two concurrent reaction pathways can account fOT the observations. One is proposed to occur in the hydrophobic phase and the other at the interfacial boundary between the hydrophobic and hy ophilic phases. Figure 6. Esterification is consider to occur at both sites so the forward rate constant will be conq)osed of the rate constants from both reactions (kf = kf + kf ). Hydrolysis (k,), on the other hand, is considered to occur primarily in solution in the hydrophobic phase whae it is limited by the solubility of water in the hydrophobic m a, as determined by the constant K2. The interface consists of a boundary between the hydrophobic and the polar regions of w/o emulsion particles, or the micelles in w/o microemulsions. In the s/i dispersions the interface is between the surface of the cation exchange resin particles and the hydrophobic medium. In either case catalysis at the interface is considered essentially irreversible while the process in the hydrophobic phase is a typical reversible esterification in solution defined by Ki in equation 1. 

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