Three-phase extraction study in the Cyanex923-n-heptane/HNO3 system

The present paper reports a study of the extraction of HNO3 with Cyancx923 (C923)-n-heptane. A third phase appears at different aqueous HNO3 concentrations for various initial C923 concentrations. Data analysis indicates that almost all of HNO3 and H2O are extracted into the middle phase. More HNO3 and water at a fixed ratio are solubilized in the reverse micelles or microemulsion in the third phase, which leads to a sharp increase of their concentration. The effect of temperature on the phase behavior of the three-phase system has also been investigated.

Monte Carlo simulation of pulsed-laser polymerization in emulsion

The pulsed-laser polymerization in emulsions has been simulated by the Monte Carlo method. Our simulation shows that the best measure of the propagation rate coefficients K-p is the peak maximum of molecular weight distribution for microemulsions when the droplets are small. However, the inflection point at the low-molecular-weight side of the peaks provides the best measure of K-p of bigger droplets. (C) 2000 Elsevier Science Ltd. All rights reserved.

Preparation and characterization of nanometer-sized CeO2/polystyrene hybrid material

Nanometer-sized CeO2/polystyrene hybrid material was prepared using reversed micelles microemulsion method. XRD analysis revealed that the CeO2 nanoparticles in polystyrene were amorphous. XPS patterns indicated that the hybrid material was not a simply physical mixture, but a certain strength of chemical bond between CeO2 nanoparticles and polystyrene existed. FTIR patterns revealed that the absorption of Ce-O bond in hybrid material was blue-shifted.

Synthesis, characterisation and applications of group IV nanocrystals

Group IV materials such as silicon nanocrystals (Si NCs) and carbon quantum dots (CQDs) have received great attention as new functional materials with unique physical/chemical properties that are not found in the bulk material. This thesis reports the synthesis and characterisation of both types of nanocrystal and their application as fluorescence probes for the detection of metal ions. In chapter 2, a simple method is described for the size controlled synthesis of Si NCs within inverse micelles having well defined core diameters ranging from 2 to 6 nm using inert atmospheric synthetic methods. In addition, ligands with different molecular structures were utilised to reduce inter-nanocrystal attraction forces and improve the stability of the NC dispersions in water and a variety of organic solvents. Regulation of the Si NCs size is achieved by variation of the surfactants and addition rates, resulting high quality NCs with standard deviations (σ = Δd/d) of less than 10 %. Large scale production of highly mondisperse Si NC was also successfully demonstrated. In chapter 3, a simple solution phase synthesis of size monodisperse carbon quantum dots (CQDs) using a room temperature microemulsion strategy is demonstrated. The CQDs are synthesized in reverse micelles via the reduction of carbon tetrachloride using a hydride reducing agent. CQDs may be functionalised with covalently attached alkyl or amine monolayers, rendering the CQDs dispersible in wide range of polar or non-polar solvents. Regulation of the CQDs size was achieved by utilizing hydride reducing agents of different strengths. The CQDs possess a high photoluminescence quantum yield in the visible region and exhibit excellent photostability. In chapter 4, a simple and rapid assay for detection of Fe3+ ions was developed, based on quenching of the strong blue-green Si NC photoluminescence. The detection method showed a high selectivity, with only Fe3+ resulting in strong quenching of the fluorescence signal. No quenching of the fluorescence signal was induced by Fe2+ ions, allowing for solution phase discrimination between the same ion in different charge states. The optimised sensor system showed a sensitive detection range from 25- 900 μM and a limit of detection of 20.8 μM

Development and application of NMR techniques to study water-in-CO2 microemulsions

Self-assembly is a phenomenon that occurs frequently throughout the universe. In this work, two self-assembling systems were studied: the formation of reverse micelles in isooctane and in supercritical CO2 (scCO2), and the formation of gels in organic solvents. The goal was the physicochemical study of these systems and the development of an NMR methodology to study them. In this work, AOT was used as a model molecule both to comprehensively study a widely researched system water/AOT/isooctane at different water concentrations and to assess its aggregation in supercritical carbon dioxide at different pressures. In order to do so an NMR methodology was devised, in which it was possible to accurately determine hydrodynamic radius of the micelle (in agreement with DLS measurements) using diffusion ordered spectroscopy (DOSY), the micellar stability and its dynamics. This was mostly assessed by 1H NMR relaxation studies, which allowed to determine correlation times and size of correlating water molecules, which are in agreement with the size of the shell that interacts with the micellar layer. The encapsulation of differently-sized carbohydrates was also studied and allowed to understand the dynamics and stability of the aggregates in such conditions. A W/CO2 microemulsion was prepared using AOT and water in scCO2, with ethanol as cosurfactant. The behaviour of the components of the system at different pressures was assessed and it is likely that above 130 bar reverse microemulsions were achieved. The homogeneity of the system was also determined by NMR. The formation of the gel network by two small molecular organogelators in toluene-d8 was studied by DOSY. A methodology using One-shot DOSY to perform the spectra was designed and applied with success. This yielded an understanding about the role of the solvent and gelator in the aggregation process, as an estimation of the time of gelation.

Physicochemical and Biochemical Characterization of Enzymes Immobilized on lnorganic Matrices

Biotechnology is currently considered as a useful altemative to conventional process technology in industrial and catalytic fields. The increasing awareness of the need to create green and sustainable production processes in all fields of chemistry has stimulated materials scientists to search for innovative catalysts supports. lmmobilization of enzymes in inorganic matrices is very useful in practical applications due to the preserved stability and catalytic activity of the immobilized enzymes under extreme conditions. Nanostructured inorganic, organic or hybrid organic-inorganic nanocomposites present paramount advantages to facilitate integration and miniaturization of the devices (nanotechnologies), thus affording a direct connection between the inorganic, organic and biological worlds. These properties, combined with good chemical stability, make them competent candidates for designed biocatalysts, protein-separation devices, drug delivery systems, and biosensors Aluininosilicate clays and layered double hydroxides, displaying, respectively, cation and anion exchange properties, were found to be attractive materials for immobilization because of their hydrophilic, swelling and porosity properties, as well as their mechanical and thermal stability.The aim of this study is the replacement of inorganic catalysts by immobilized lipases to obtain purer and healthier products.Mesocellular silica foams were synthesized by oil-in-water microemulsion templating route and were functionalized with silane and glutaraldehyde. " The experimental results from IR spectroscopy and elemental analysis demonstrated the presence of immobilized lipase and also functionalisation with silane and glutaraldehyde on the supports.The present work is a comprehensive study on enzymatic synthesis of butyl isobutyrate through esterification reaction using lipase immobilized onto mesocellular siliceous foams and montmorillonite K-10 via adsorption and covalent binding. Moreover, the irnrnobil-ization does not modify the nature of the kinetic mechanism proposed which is of the Bi-Bi Ping—Pong type with inhibition by n-butanol. The immobilized biocatalyst can be commercially exploited for the synthesis of other short chain flavor esters. Mesocellular silica foams (MCF) were synthesized by microemusion templating method via two different routes (hydrothermal and room temperature). and were functionalized with silane and glutaraldehyde. Candida rugosa lipase was adsorbed onto MCF silica and clay using heptane as the coupling medium for reactions in non-aqueous media. I From XRD results, a slight broadening and lowering of d spacing values after immobilization and modification was observed in the case of MCF 160 and MCF35 but there was no change in the d-spacing in the case of K-10 which showed that the enzymes are adsorbed only on the external surface. This was further confirmed from the nitrogen adsorption measurements

Molecular guided catalytic hydrogenation by micelle-hosted Pd nanoparticle in supercritical CO2

Homogeneous dispersion of microemulsion containing palladium nanoparticles in scCO(2) is, for the first time, observed via sapphire window reactor and these particles show an unusual reluctance for double bond hydrogenation of citral aldehyde at hydrophobic end rather than hydrophilic end (high regioselectivity) owing to the unique micelle environment in supercritical carbon dioxide that guide a head-on attack of the molecule.

Micelle-hosted palladium nanoparticles catalyze citral molecule hydrogenation in supercritical carbon dioxide

A new approach of employing metal particles in micelles for the hydrogenation of organic molecules in the presence of fluorinated surfactant and water in supercritical carbon dioxide has very recently been introduced. This is allegedly to deliver many advantages for carrying out catalysis including the use of supercritical carbon dioxide (scCO(2)) as a greener solvent. Following this preliminary account, the present work aims to provide direct visual evidence on the formation of metal microemulsions and to investigate whether metal located in the soft micellar assemblies could affect reaction selectivity. Synthesis of Pd nanoparticles in perfluorohydrocarboxylate anionic micelles in scCO(2) is therefore carried out in a stainless steel batch reactor at 40 degreesC and in a 150 bar CO2/H-2 mixture. Homogeneous dispersion of the microemulsion containing Pd nanoparticles in scCO(2) is observed through a sapphire window reactor at W-0 ratios (molar water-to-surfactant ratios) ranging from 2 to 30. It is also evidenced that the use of micelle assemblies as new metal catalyst nanocarriers could indeed exert a great influence on product selectivity. The hydrogenation of a citral molecule that contains three reducible groups (aldehyde, double bonds at the 2,3-position and the 6,7-position) is studied. An unusually high selectivity toward citronellal (a high regioselectivity toward the reduction of the 2,3-unsaturation) is observed in supercritical carbon dioxide. On the other hand, when the catalysis is carried out in the conventional liquid or vapor phase over the same reaction time, total hydrogenation of the two double bonds is achieved. It is thought that the high kinetic reluctance for double bond hydrogenation of the citral molecule at the hydrophobic end (the 6,7-position) is due to the unique micelle environment that is in close proximity to the metal surface in supercritical carbon dioxide that guides a head-on attack of the molecule toward the core metal particle.

Aerogel-coated metal nanoparticle colloids as novel entities for the synthesis of defined supported metal catalysts

Nanometer metal particles of tailored size (3-5 nm) and composition prepared via inverse microemulsion were encapsulated by ultrathin coatings (<2.5 nm) of inorganic porous aerogels covered with surface -OH groups. These composite materials formed metastable colloids in solvent(s), and the organic surfactant molecules were subsequently removed without leading to aggregation (the ethanolic colloid solution was shown to be stable against flocculation for at least weeks). We demonstrate that the totally inorganic-based composite colloids, after the removal of surfactant, can be anchored to conventional solid supports (gamma-alumina, carbons) upon mixing. Application of a high temperature resulted in the formation of strong covalent linkages between the colloids and the support because of the condensation of surface groups at the interface. Detailed characterizations (X-ray diffraction (XRD), pore analysis, transmission electron microscopy (TEM), CO chemisorption) and catalytic testing (butane combustion) showed that there was no significant metal aggregation from the fine metal particles individually coated with porous aerogel oxide. Most of these metal sites on the coated nanoparticles with and without support are fully accessible by small molecules hence giving extremely active metal catalysts. Thus, the product and technology described may be suitable to synthesize these precursor entities of defined metal sizes (as inks) for wash coat/impregnation applications in catalysis. The advantages of developing inorganic nanocomposite chemical precursors are also discussed.

Phospholipid-based microemulsions suitable for use in foods

The preparation of nonaqueous microemulsions using food-acceptable components is reported. The effect of oil on the formation of microemulsions stabilized by lecithin (Epikuron 200) and containing propylene glycol as immiscible solvent was investigated. When the triglycerides were used as oil, three types of phase behavior were noted, namely, a two-phase cloudy region (occurring at low lecithin concentrations), a liquid crystalline (LC) phase (occurring at high surfactant and low oil concentrations), and a clear monophasic microemulsion region. The extent of this clear one-phase region was found to be dependent upon the molecular volume of the oil being solubilized. Large molecular volume oils, such as soybean and sunflower oils, produced a small microemulsion region, whereas the smallest molecular volume triglyceride, tributyrin, produced a large, clear monophasic region. Use of the ethyl ester, ethyl oleate, as oil produced a clear, monophasic region of a size comparable to that seen with tributyrin. Substitution of some of the propylene glycol with water greatly reduced the extent of the clear one-phase region and increased the extent of the liquid crystalline region. In contrast, ethanol enhanced the clear, monophasic region by decreasing the LC phase. Replacement of some of the lecithin with the micelle-forming nonionic surfactant Tween 80 to produce mixed lecithin/Tween 80 mixtures of weight ratios (Km) 1:2 and 1:3 did not significantly alter the phase behavior, although there was a marginal increase in the area of the two-phase, cloudy region of the phase diagram. The use of the lower phosphatidylcholine content lecithin, Epikuron 170, in place of Epikuron 200 resulted in a reduction in the LC region for all of the systems investigated. In conclusion, these studies show that it is possible to prepare one-phase, clear lecithin-based microemulsions over a wide range of compositions using components that are food-acceptable.

Fluorinated ionic surfactant microemulsions in hydrofluorocarbon 134a (HFC 134a)

The factors influencing the formation of water-in-134a-propellant microemulsions using the fluorinated ionic surfactants ammonium perfluorooctanoate, ammonium perfluoroheptanoate, and sodium perfluorooctanoate has been determined. None of the fluorinated ionic surfactants could be used to prepare clear, one-phase systems when used as sole surfactant, but they could be when combined with a short-chain fluoro- or hydrocarbon alcohol in surfactant:cosurfactant weight-mixing ratios (K(m)) in the range 1:2 to 2:1. When hydrocarbon alcohols were used this clear region extended over a wide range of compositions and was confirmed by means of photon correlation spectroscopy (PCS) to contain microemulsion droplets in the propellant-rich part of the phase diagram. PCS studies performed in the presence of the water-soluble drug terbutaline sulfate showed that it was possible to solubilize the drug within water-in-propellant microemulsion droplets. These studies confirm for the first time that it is possible to prepare water-in-propellant 134a microemulsions using fluorinated ionic surfactants and to solubilize water-soluble drugs within these systems.

Formation of fluorinated nonionic surfactant microemulsions in hydrofluorocarbon 134a (HFC 134a)

A structurally related series of fluorinated nonionic oxyethylene glycol surfactants of the type C(m)F(2m+1)(CH(2))(n)O[(CH(2)CH(2)O)(p)H], denoted C(m.n)E(p) (where m=4, 6, or 7, m=1 or 2, and p=4 or 6) were synthesized and their surface behavior in aqueous solution was characterized. The ability of these surfactants to form water-in-hydrofluorocarbon (HFC) propellant 134a microemulsions suitable for use in the aerosolized delivery of water-soluble drugs has been investigated. Phase studies showed that, regardless of the composition used, clear one-phase systems could not be prepared if a fluorinated nonionic surfactant was used alone, or in combination with a short or medium fluorocarbon alcohol cosurfactant. Clear one-phase systems could, however, be prepared if a short-chain hydrocarbon alcohol, such as ethanol, n-propanol, or n-pentanol, was used as cosurfactant, with the extent of the one-phase region increasing with decreased chain length of the alcohol cosurfactant. Light-scattering studies on a number of the hydrocarbon-alcoholcontaining systems in the propellant-rich part of the phase diagram showed that only systems prepared with C(4.2)E(6) and propanol contained microemulsion droplets (all other systems investigated were considered to be cosolvent systems).

Investigations into the formation and characterization of phospholipid microemulsions. IV. Pseudo-ternary phase diagrams of systems containing water-lecithin-alcohol and oil; The influence of oil

Phase studies have been performed for quaternary systems composed of egg lecithin, cosurfactant, water and oil. The lecithin used was the commercially available egg lecithin Ovothin 200 (which comprises ≥ 92% phosphatidylcholine). The cosurfactants employed were propanol and butanol, and these were used at lecithin/cosurfactant mixing ratios (Km) of 1:1 and 1.94:1 (weight basis). Six polar oils were investigated, including the alkanoic acids, octanoic and oleic, their corresponding ethyl esters and the medium and long chain triglycerides, Miglyol 812 and soybean oil. All oils, irrespective of the alcohol and the Km used, gave rise to systems that produced a stable isotropic region along the surfactant/oil axis (designated as a reverse microemulsion system). In addition, the systems incorporating propanol at both Km and butanol at a Km of 1.94: 1, generally gave rise to a liquid crystalline region and, in some cases, a second isotropic non-birefingent area (designated as a normal microemulsion system). The phase behaviour observed was largely dependent upon the alcohol and Km used and the size and the polarity of the oil present.

Improving polymeric microemulsions with block copolymer polydispersity

Recent experiments have demonstrated that block copolymers are capable of stabilizing immiscible homopolymer blends producing bicontinuous microemulsion. The stability of these polymeric alloys requires the copolymer to form flexible, nonattractive monolayers along the homopolymer interfaces. We predict that copolymer polydispersity can substantially and simultaneously improve the monolayers in both of these respects. Furthermore, polydispersity should provide similar improvements in systems, such as colloidal suspensions and polymer/clay composites, that utilize polymer brushes to suppress attractive interactions.