Search results for "Chemical engineering"
showing 10 items of 5892 documents
Favoring alkane primary carbon-hydrogen bond functionalization in supercritical carbon dioxide as reaction medium
2019
The selectivity of a catalytic alkane functionalization process can be modified just changing the reaction medium from neat alkane to supercritical carbon dioxide (scCO2). A silica supported copper complex bearing an Nheterocyclic carbene ligand promotes the functionalization of carbon-hydrogen bonds of alkanes by transferring the CHCO2Et group from N2=CHCO2Et (ethyl diazoacetate, EDA). In neat hexane only 3% of the primary C-H bonds (ethyl heptanoate being the product) are functionalized in that manner, whereas the same reaction carried out in scCO2 provides a 30% yield in this linear ester. Such effect seems to be induced by an electronic density flux from the NHC ligand to the surroundin…
Analytical methods for the characterization and determination of nonionic surfactants in cosmetics and environmental matrices
2013
Nonionic synthetic surfactants, constituted of an assortment of classes, are common ingredients of industrial, household and body-care products. Alone or in combination with anionic surfactants, they perform a variety of functions including cleaning action, emulsification, skin conditioning, appearance and consistency modification, solubilization and dispersing agents. By far fatty alcohol ethoxylates (AEs) and alkylphenol ethoxylates (APEs) are more extensively used than any other nonionic surfactant class; however, works appearing in the literature making reference to the analysis of other nonionic surfactant classes have also been collected in this review. The production volume worldwide…
Organized assemblies of magnetic clusters
2003
Abstract In this work we have explored the possibilities to create layered organizations of the Mn 12 single-molecule magnets using the Langmuir–Blodgett technique or attaching these clusters onto a metal surface by preparing self-assembled monolayers (SAMs). In the first part we discuss the use of the Langmuir–Blodgett (LB) technique in order to obtain organized magnetic films formed by monolayers of these clusters. Two strategies have been used with this aim. The first one consists of mixing Mn 12 acetate or benzoate derivatives with an amphiphile, while the second procedure is based on the use of Mn 12 derivatives specifically designed to form LB films. An alternative method is that of p…
Influence of initial treatments of aluminium on the morphological features of electrochemically formed alumina membranes
2003
Abstract The fabrication of alumina membranes by electrochemical oxidation of annealed aluminium was investigated. Porous layers were grown in 0.4 M H3PO4 at −1 and 5 °C at different anodising times. The morphology of the outer surface was found to be dependent on temperature and charge density, with both determining the extent of chemical dissolution of the anodic oxide. The inner-surface morphology was found to depend on the applied voltage only. The chemical dissolution rate of anodic oxide grown on annealed aluminium was found to be lower than that formed on unannealed aluminium under otherwise identical conditions. Such a difference in behaviour is explained in terms of a higher finish…
Pyroxene-based glass-ceramics as glazes for floor tiles
2005
Abstract Crystallization of a glass with composition in the diopside primary crystallization field in the MgO–CaO–Al 2 O 3 –SiO 2 quaternary system was investigated. Also the action of some additives, nucleants and fluxes, in the pyroxene development was examined. Glasses were prepared by conventional melting of a mixture of raw materials and cooled by pouring in water. Pellets of glass powder specimens were thermally treated at several temperatures up to 1200 °C. The crystallization path was followed by X-ray diffraction powder (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The results proved that, in addition to the effect of B 2 O 3 and TiO 2 in…
Effect of NiO and/or TiO2 mullite formation and microstructure from gels
1998
Polymeric and colloidal gels with a constant molar ratio of (Al+Ni and/or Ti)/Si=3/1 and various (Al/Ni and/or Ti) ratios (up to 21.42 mol% NiO+TiO2) were prepared and used to study the effect of the precursor chemical homogeneity on mullite formation processes and the resulting microstructure. Both kinds of gel precursors were preheated at 750°C for 3 h in order to obtain appropriate gel-derived glasses for further thermal processing. After annealing for several time periods at temperatures between 750 and 1500°C, differences in crystallization pathways were observed. Polymeric gels crystallized Al–Si and NiAl2O4 spinels from the amorphous form at temperatures in the range between 900 and …
Selective adsorption of oppositely charged PNIPAAM on halloysite surfaces: a route to thermo-responsive nanocarriers.
2018
Halloysite nanotubes were functionalized with stimuli-responsive macromolecules to generate smart nanohybrids. Poly(N-isopropylacrylamide)-co-methacrylic acid (PNIPAAM-co-MA) was selectively adsorbed into halloysite lumen by exploiting electrostatic interactions. Amine-terminated PNIPAAM polymer was also investigated that selectively interacts with the outer surface of the nanotubes. The adsorption site has a profound effect on the thermodynamic behavior and therefore temperature responsive features of the hybrid material. The drug release kinetics was investigated by using diclofenac as a non-steroidal anti-inflammatory drug model. The release kinetics depends on the nanoarchitecture of th…
On the formation of inclusion complexes at the solid/liquid interface of anchored temperature-responsive PNIPAAM diblock copolymers with γ-cyclodextr…
2017
The thermal responsive behavior of adsorbed layers of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAAM) and poly((3-acrylamidopropyl)trimethylammonium chloride) (PAMPTMA(+)) with γ-cyclodextrin (γ-CD) at the solid/liquid interface has been investigated using three in situ techniques: null ellipsometry, quartz–crystal microbalance with dissipation monitoring, and neutron reflectometry. The measurements provided information about the adsorbed amounts, the layer thickness, hydration and viscoelastic properties, and the interfacial structure and composition. The copolymers adsorb to silica with the cationic PAMPTMA(+) blocks sitting as anchors in a flat conformation and the PNIPAAM ch…
Nontemplate Synthesis of CH3NH3PbBr3 Perovskite Nanoparticles
2014
To date, there is no example in the literature of free, nanometer-sized, organolead halide CH3NH3PbBr3 perovskites. We report here the preparation of 6 nm-sized nanoparticles of this type by a simple and fast method based on the use of an ammonium bromide with a medium-sized chain that keeps the nanoparticles dispersed in a wide range of organic solvents. These nanoparticles can be maintained stable in the solid state as well as in concentrated solutions for more than three months, without requiring a mesoporous material. This makes it possible to prepare homogeneous thin films of these nanoparticles by spin-coating on a quartz substrate. Both the colloidal solution and the thin film emit l…
Templated growth of smart nanocomposite thin films: Hybrid aerosol assisted and atmospheric pressure chemical vapour deposition of vanadyl acetylacet…
2009
Hybrid aerosol assisted and atmospheric pressure chemical vapour deposition methodology has been utilised to produce nanocomposite thin films of gold nanoparticles and vanadium dioxide from vanadyl acetylacetonate and auric acid. The addition of tetraoctyl ammonium bromide (TOAB) to the precursor Solution gave control of the size and distribution of gold nanoparticles in the vanadium oxide matrix. These reactions led to vanadium dioxide films with reduced crystallite sizes and enhanced thermochromic properties. The films were analysed by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Their optical and thermochromic behaviour was also determined, This h…