Microemulsion utilization

Husein, M., Rodil, E. and Vera, J.H. (2004) Formation of silver bromide precipitate of nanoparticles in a single microemulsion utilizing the surfactant counterion. /. Colloid Interface Sci., 273,... 

Similar threshold phenomena have been reported for the reduction of persulfate in reverse microemulsion polymerization of acrylamide [12,13], for ferrocyanide oxidation in similar microemulsions utilizing acetonitrile as cosurfactant [29], and for the autocatalytic oxidation of acrylamide and a variety of primary alkylamides where the respective amides served as cosurfactant [31]. 

The draft-tube airlift bioreactor was studied using water-in-kerosene microemulsions [263], The effect of draft tube area vs. the top-section area on various parameters was studied. The effect of gas flow rates on recirculation and gas carry over due to incomplete gas disengagement were studied [264], Additionally, the effect of riser to downcomer volume was also studied. The effect of W/O ratio and viscosity was tested on gas hold-up and mass transfer coefficient [265], One limitation of these studies was the use of plain water as the aqueous phase in the cold model. The absence of biocatalyst or any fermentation broth from the experiments makes these results of little value. The effect of the parameters studied will greatly depend on the change in viscosity, hold-up, phase distribution caused due to the presence of biocatalyst, such as IGTS8, due to production of biosurfactants, etc., by the biocatalyst. Thus, further work including biocatalyst is necessary to truly assess the utility of the draft-tube airlift bioreactor for biodesulfurization. 

Two main microemulsion microstructures have been identified droplet and biconti-nuous microemulsions (54-58). In the droplet type, the microemulsion phase consists of solubilized micelles reverse micelles for w/o systems and normal micelles for the o/w counterparts. In w/o microemulsions, spherical water drops are coated by a monomolecular film of surfactant, while in w/o microemulsions, the dispersed phase is oil. In contrast, bicontinuous microemulsions occur as a continuous network of aqueous domains enmeshed in a continuous network of oil, with the surfactant molecules occupying the oil/water boundaries. Microemulsion-based materials synthesis relies on the availability of surfactant/oil/aqueous phase formulations that give stable microemulsions (54-58). As can be seen from Table 2.2.1, a variety of surfactants have been used, as further detailed in Table 2.2.2 (16). Also, various oils have been utilized, including straight-chain alkanes (e.g., n-decane, /(-hexane),... 

The work of Mallouk et al. (39) offers an interesting extension of the microemulsion sol-gel technique. In this case, microemulsion-derived silica nanoparticles were used as templates for preparing ordered mesoporous polymers with tailored pore sizes. Utilizing the Triton N-101/cyclohexane/hexanol/water/ammonia microemulsion, monodisperse silica nanoparticles were first synthesized. The silica product... 

Silica Gels. The acid-catalyzed alkoxide sol-gel process produces gels (17). Frib-erg and coworkers (40-50) pioneered the extension of this process to silica synthesis in microemulsions both aqueous and nonaqueous microemulsions were used. For aqueous microemulsions, experiments were conducted mostly with the SDS/ pentanol/water/acid system. A representative flow diagram is shown in Figure 2.2.9. The nonaqueous microemulsion systems utilized included CTAB/decanol/ decane/formamide and AOT/decane/glycerol (44-46,49,50). The experimental approach followed the sequence nonaqueous microemulsion preparation, water addition, and then TEOS addition. 

Description of the different mimetic systems will be the starting point of the presentation (Sect. 2). Preparation and characterization of monolayers (Langmuir films), Langmuir-Blodgett (LB) films, self-assembled (SA) mono-layers and multilayers, aqueous micelles, reversed micelles, microemulsions, surfactant vesicles, polymerized vesicles, polymeric vesicles, tubules, rods and related SA structures, bilayer lipid membranes (BLMs), cast multibilayers, polymers, polymeric membranes, and other systems will be delineated in sufficient detail to enable the neophyte to utilize these systems. Ample references will be provided to primary and secondary sources. 

Membrane-mimetic compartments have provided a viable means for generating monodispersed catalytic particles [500], In particular, reversed micelles and microemulsions have been used extensively as hosts. A complete summary of work reported on the in situ generation of catalysts in membrane-mimetic media, including publications up to 1987, has been produced [500] and, therefore, will not be reiterated here. Attention will be focused on more recent research utilizing monolayers, bilayer lipid membranes (BLMs), Langmuir-Blodgett (LB) films, zeolites, and clay particles as membrane-mimetic templates. 

Our synthesis is based on the hydrolysis of a silicon alkoxide (TEOS Si(OCH2CH3)4) in a diluted solution of nonionic polyethylene oxide-based surfactants. The hydrolysis is then induced by the addition of a small amount of sodium fluoride [5], Depending on the initial mixing conditions, the size of the solubilized objects leads to either a colorless or milky emulsion. Small particles ( 300 nm) with a 3D worm-hole porous structure or small hollow spheres with mesoporous walls, are usually obtained [6]. The synthesis we report herein after exhibits an apparently slight but actually drastic change in the preparation conditions. The main feature of this approach is an intermediate step that utilizes a mild acidity (pH 2 - 4), in which, prior to the reaction, a stable colorless microemulsion containing all reactants is... 

Different aspects involved in the design of artificial photosynthetic systems have been discussed. Charged colloids and water-oil microemulsions provide effective organized media for controlling photosensitized electron transfer processes. Development of catalysts capable of utilizing the photoproducts in chemical routes, particularly in multi-electron fixation processes is of major... 

Future work in this area should focus on further development of novel extraction schemes that exploit one or more of the cited advantages of the nonionic cloud point method. It is worth noting that certain ionic, zwitterionic, microemulsion, and polymeric solutions also have critical consolution points (425,441). There appear to be no examples of the utilization of such media in extractions to date. Consequently, the use of some of these other systems could lead to additional useful concentration methods especially in view of the fact that electrostatic interactions with analyte molecules is possible in such media whereas they are not in the nonionic surfactant systems. The use of the cloud point event should also be useful in that it allows for enhanced thermal lensing methods of detection. 

This chapter describes novel inkjet inks based on a variety of vehicles, and demonstrates several optical applications utilized by inkjet inks. It aims to provide a general description of inks which are based on unique components and structures, mainly micellar systems, polyelectrolyte complexes, microemulsions, miniemulsions, emulsions, liquid crystals, and interesting phase... 

Utilization of mlcroemulslons would appear to be one method by which the polymerization problem might be reduced or even eliminated. In a water-in-oil microemulsion we would expect the ii)-hydroxy- and u-bromoacids to be compartmentalized on a molecular basis l.e. an average of one molecule per drop up to some concentration, then two per drop, etc., and movement between drops inhibited. As a consequence since the base is soluble in water and the acid likely located in the interphase we would expect that the chance of ring closure before dimerization, tri-merization, etc., would be greatly enhanced over that existing in homogeneous media. 

The microemulsion method utilizes a water/oil/surfactant system to construct a micro reactor, in which NCs could be s)mthesized. The microemulsions have a wide range of applications from oil recovery fo fhe s)mfhesis of nanoparticles. Microemulsion is a system of water, oil, and surfactant, and it is an optically isotropic and thermod3mamically stable solution. At molecular scale, the microemulsion is heterogeneous with an internal structure either of nanospherical monosized droplefs (micelles or reverse micelles) or a bicontinuous phase, depending on the given temperature as well as the ratio of its constituents (Eriksson et al., 2004). The small droplets could be utilized as microreactors in order to s)mthesize the fine NCs in a controllable way. 

Finally, by adjunction of a cross-linking compound in the disperse phase of the microemulsion it is possible to prepare microgels which can be utilized as water-retention agents (13,26). 

Most of the early work involving microemulsions in supercritical fluids utilized the supercritical alkanes, ethane and propane, with the surfactant AOT. Table 1 gives a summary of the surfactant systems that have been studied in supercritical hydrocarbon solvents. More recently, there has been some success with the formation of... 

Larson KA and Wiencek JM. Mercury removal from aqueous streams utilizing microemulsion Uquid membranes. Environ Progress 1994 13 253-262. 

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