1,721,077 research outputs found
Silicate Glass Coated Microchannels through Phase Conversion Process for Glass-Like Electrokinetic Performance
No full textThe surface modified polydimethylsiloxane (PDMS) microchannels show a much more inferior performance to the durable and reproducible glass chip. In this paper, a facile approach to preparing a silicate glass modified PDMS microchannel for glass-like performance is presented. This glass-like performance is made possible by a phase conversion of a preceramic polymer - allylhydridopolycarbosilane (AHPCS). The, several hundred nanometer thick, polymer that coats the PDMS channel is hydrolyzed to form hydrophilic silicate glass via phase conversion under an aqueous alkali condition. It is characterized by XPS, FTIR-ATR, AFM, and contact angle measurements. The silicate glass coated PDMS channel from AHPCS has an excellent solvent resistance, delivers a high electroosmotic flow (EOF) that is stable in the long-term (4.9 +/- 0.1 x 10(-4) cm(2) V(-1) s(-1)) and a reliable capillary electrophoresis (CE), which are comparable to those of native glass channels. Moreover, the silicate glass PDMS channel allows easy regeneration of the electrokinetic behavior, just as in a glass channel, by a simple treatment with alkali solution. This coating approach can be applied to other polymer substrates such as polyimide (PI).open112625sciescopu
Direct Preparation of High Surface Area Mesoporous SiC-Based Ceramic by Pyrolysis of a Self-Assembled Polycarbosilane-block-Polystyrene Diblock Copolymer
No full textDirect pyrolysis of a self-assembled inorganic-organic block copolymer can be a promising route for fabricating the ordered ceramic nanostructures based on the achievements of organic-organic block copolymers. Here we report the synthesis of a novel polycarbosilane-block-polystyrene diblock copolymer by ring-opening living anionic polymerization in a THF and n-hexane solvent system at similar to 48 degrees C. The resulting block copolymer revealed phase-separation behavior in the nanoscale to form a self-assembled nanostructure that was converted to a mesoporous ceramic phase after heating at 800 degrees C. The pyrolyzed ceramic product exhibited well-ordered mesoporous SiC-based ceramic structures with a high BET surface area of 1325 m(2) g(-1) and an average mesopore size of 7.8 nm containing a large amount of micropores.X112930sciescopu
A Microchemical System with Continuous Recovery and Recirculation of Catalyst-Immobilized Magnetic Particles
No full textX1128sciescopu
Dual-Channel Microreactor for Gas-Liquid Syntheses
No full textA microreactor consisting of two microfluidic channels that are separated by a thin membrane is devised for intimate contact between gas and liquid phases. Gas flowing in one microchannel can diffuse into the liquid flowing in the other microchannel through the thin membrane. An oxidative Heck reaction carried out in the dual-channel (DC) microreactor, in which gaseous oxygen plays a key role in the catalytic reaction, shows the significant improvement that can be made over the traditional batch reactor and the conventional segmental microreactor in terms of yield, selectivity, and reaction time. It also allows independent control of the flow of the gaseous reagent. The proposed DC microreactor should prove to be a powerful tool for fully exploring gas liquid microchemistry.X116363sciescopu
Direct preparation of mesoporous carbon by pyrolysis of poly(acrylonitrile-b-methylmethacrylate) diblock copolymer
No full textDirect pyrolysis of self-assembled polyacrylonitrile-block-polymethylmethacrylate (PAN-b-PMMA) diblock copolymer can be a promising route for fabricating an ordered carbon nanostructure. PAN-b-PMMA diblock copolymer was synthesized successfully by atom transfer radical (ATRP) polymerization in DMF at 90 degrees C with well-controlled molecular weight and narrow polydispersity. The resulting block copolymer self-assembled in the mixture of ethanol and water to form nanoparticles with a narrow size distribution. Furthermore, the high quality of the as-synthesized PAN-b-PMMA block copolymer experienced phase-separation to form a self-assembled nanostructure at 250 degrees C that was converted to a mesoporous carbon phase after heating at 800 degrees C. The pyrolyzed carbon product exhibited well-defined nanostructure with a high BET surface area of 860 m(2) g(-1) and an average mesopore size of 8.1 nm.open11111sciescopu
Efficient and continuous monoacylation with superior selectivity of symmetrical diamines in microreactors
No full textEfficient and continuous monoacylation of symmetrical diamines performed in microreactors yielded superior selectivity to that predicted by statistical considerations. It is highly valuable that the kinetically controlled product in high yields was achieved without any special catalyst at ambient temperature.open111112sciescopu
Surface Plasmon Induced Visible Light Photocatalytic Activity of TiO2 Nanospheres Decorated by Au Nanoparticles with Controlled Configuration
No full textThis work is focused on the development of a surface plasmon-induced visible light active photocatalyst system composed of silica-titania core-shell (SiO2@TiO2) nanostructures decorated with Au nanoparticles (Au NPs). The influence of size and distribution of Au NPs on photocatalysis, its fabrication methods, and exploration of the mechanism of visible light activity were investigated. A favorable architecture of SiO2 beads with a thin layer of TiO2 was decorated with Au NP arrays having different size and areal density. Surface modification of SiO2@TiO2 leads to a viable and homogeneous loading of Au NPs on the surface of TiO2, which renders visible light-induced photocatalytic activity on the whole TiO2 surface. An optimized system employing Au NP arrays with 15 nm size and 700/mu m(2) density showed best catalytic efficiency due to a synergistic effect of the firm contact between Au NPs and TiO2 and efficiently coupled SPR excitation. A brief mechanism relating the electron transfer from surface-plasmon-stimulated Au NPs to the conduction band of TiO2 is proposed.X11170164sciescopu
Computational simulation on steric hindrance between hydrophobic tails of lamellar matrix composed of acyl glutamate/stearyl alcohol/behenyl alcohol by molecular
No full textMonosodium N-stearoyl-L-glutamate (MSSG), an amino acid surfactant, could associate with higher alcohols such as stearyl alcohol (SA) and behenyl alcohol (BA) and they were self-assembled into a lamella in an aqueous phase. When MSSG, SA and BA were assumed to associate each other in molar ratios of 1:1:1, 1:2:1, 1:1:2, 1:2:2 and 1:1:3, the packing parameter of each associate was calculated using molecular dynamics (MD). Among them, only 1:1:1 associate and 1:1:3 one exhibited packing parameters of around 1. According to the result of colloidal stability, however, the lamella composed of 1:1:3 associate was poorly stable while that of 1:1:1 associate was stable. In order to explain why the colloidal stability is not related to the packing parameter, the concept of steric compressibility was introduced. Steric compressibility is a measure of vertical steric hindrance occurred between hydrophobic tails of lamella. The value of steric compressibility, calculated by MD, of 1:1:1 and 1:1:3 associates were 4.7 and 8.2, respectively. That is, the vertical repulsion in the lamella of 1:1:3 associate might be greater than in the lamella of 1:1:1 associate. This would account for why the lamella of 1:1:3 associate is poorly stable even though the packing parameter is almost 1. Besides the condition that packing parameter is to be around 1, the steric compressibility of lamella should be as low as possible to achieve a stable lamella. (C) 2008 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V All rights reserved.X110sciescopuskc
Heterogeneous PdAg alloy catalyst for selective methylation of aromatic amines with formic acid under an additive-free and solvothermal one-pot condition
Full text linkThe methylation of amines for the synthesis of methylamines and dimethylamines as platform chemicals has been attempted mostly by homogeneous catalysts with acid additives. However, there are scarcely any reports on heterogeneous catalytic methylation reactions except for a routine approach under high temperature and high pressure of CO2 and H-2 gases for extended reaction times. Here we report a heterogeneously catalyzed selective methylation of aromatic amines using reactive and nontoxic formic acid as the only source for the construction of methyl groups, under ambient pressure in an additive-free one-pot reaction condition. Equal proportions of Pd and Ag in the PdAg/Fe3O4/N-rGO catalyst deliver highly selective amine methylation without aromatic ring hydrogenation, as the strained Pd in the alloy is combined with the graphene-derived support, preventing nanoparticle agglomeration and the action of magnetite as a promoter. Both N-methylation and N, N-dimethylation of various substituted aromatic amines were performed with complete conversion and excellent 90-97% selectivity by controlling the reaction times in the range of 10-24 h at 140 degrees C without unwanted aromatic ring hydrogenation. Furthermore, the developed bimetallic catalyst provided high yields (88-91%) of methylation with CO2+H-2 gas under high pressure, which are as good as the results of homogenous catalysts with an acid additive. To the best of our knowledge, our use of this environmentally friendly methodology is the first time that this durable heterogeneous catalyst has readily performed highly selective methylation at ambient pressure, which is attractive for industrial applications.1193Ysciescopu
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