Institute of Condensed Matter and Nanosciences IMCN

Louvain-la-Neuve, Belgium

Institute of Condensed Matter and Nanosciences IMCN

Louvain-la-Neuve, Belgium
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Kumar L.,Central University of Jharkhand | Kumar P.,Indian Institute of Technology Patna | Srivastava S.K.,Institute of Condensed Matter and Nanosciences IMCN | Kar M.,Indian Institute of Technology Patna
Journal of Superconductivity and Novel Magnetism | Year: 2014

The DC magnetic hysteresis loop measurements were carried out for temperatures varying from 5 to 300 K over a field range of ±10 T on nanocrystalline ( 35 nm) cobalt ferrite samples (crystallized to Fd 3 m Fd\bar {3} m space group with cubic symmetry) to validate the law of approach at low temperature for the nanocrystalline cobalt ferrite. A magnetocrystalline anisotropy constant and saturation magnetization have been obtained by analyzing the magnetization curve in saturation using the "law of approach (LA) to saturation." The magnetocrystalline anisotropy constant is found to be almost constant in the temperature range of 5 to 150 K due to the freezing of spin at low temperature. Also, spin freezing leads to a decrease of coercivity with the increase in the temperature. © 2014 Springer Science+Business Media New York.

Ghoos T.,Hasselt University | Van Den Brande N.,Vrije Universiteit Brussel | Defour M.,Vrije Universiteit Brussel | Brassinne J.,Institute of Condensed Matter and Nanosciences IMCN | And 13 more authors.
European Polymer Journal | Year: 2014

Amphiphilic diblock copolythiophenes are synthesized by an efficient two-step synthetic strategy. The block architecture is created via the quasi-living Grignard metathesis reaction, after which ionic imidazolium moieties are introduced by substitution on the bromohexyl side chains of one of the monomer constituents. The compositional influence on the solution behavior and thermal properties of both the precursor and ionic block copolythiophenes is investigated. The novel materials are of particular appeal for integration in organic solar cell stacks, either as active layer or interlayer materials. © 2014 Elsevier Ltd. All rights reserved.

Baldovino-Medrano V.G.,Institute of Condensed Matter and Nanosciences IMCN | Le M.T.,Institute of Condensed Matter and Nanosciences IMCN | Van Driessche I.,Hanoi University of Science and Technology | Bruneel E.,Ghent University | And 6 more authors.
Catalysis Today | Year: 2015

The process and impact of shaping mixed vanadium aluminum (hydr)oxides, VAlOH and VAlO, respectively, and BiMo catalysts by tableting and slip-casting were examined. Graphite (G) was employed as a shaping agent for tableting. Without it tableting was impracticable. Graphite was found to enhance the mechanical resistance of VAlOH-xG and BiMo-xG and changed the surface area by increasing it for the non-porous BiMo and by decreasing it for the mesoporous VAlOH. In addition, graphite modified the catalytic performance despite changing neither the chemical nor the structural state of the base VAlO(H) and BiMo catalysts. A positive effect on the performance of VAlO-xG in propane oxidative dehydrogenation was found. It was proposed that catalytic active sites are formed on graphite during calcination. Conversely, graphite was harmful for non-calcined VAlOH-xG and BiMo-xG. On the other hand, the preparation of chemically and physically stable VAlO(H) suspensions for slip-casting was accomplished. Chemical stability was achieved at pHs near the isoelectric point of these catalysts. For physical stability, the use of a dispersing agent, poly(acrylic acid), combined with a control of the solids concentration was necessary. A simple and reliable method for preparing VAlOH and BiMo pellets by slip-casting was thus developed with the use of colloidal silica as binding agent. The so prepared pellets were mechanically resistant and kept the surface area of the base materials. A decrease in the surface concentration of the active metals due to surface active site masking by silicon for VAlOH-xSi and BiMo-xSi led to an inferior catalytic performance. © 2014 Elsevier B.V. All rights reserved.

Ghoos T.,Hasselt University | Brassinne J.,Institute of Condensed Matter and Nanosciences IMCN | Fustin C.-A.,Institute of Condensed Matter and Nanosciences IMCN | Gohy J.-F.,Institute of Condensed Matter and Nanosciences IMCN | And 9 more authors.
Polymer (United Kingdom) | Year: 2013

A series of ionic polythiophenes, in homopolymer and random copolymer configurations, is prepared via the Grignard metathesis (GRIM) polymerization protocol and subsequent substitution on the bromohexyl side chains with N-methylimidazole. The introduced structural variations - comonomer ratio, side chain composition, counter ions - allow tuning of the thermal properties and solution behavior of the resulting conjugated polymers. As expected, the solubility depends majorly on the number of ionic groups and the counter ions. The most peculiar behavior is observed for the P3HT-P3(MIM)HT-Br 50/50 random copolymer, which shows organization of the polymer chains in solution and thin film dependent on the preparation conditions. Dynamic light scattering studies confirm that the ordered solid-state structure is somewhat maintained when the copolymer is dissolved in a bad solvent mixture. The ionic (co)polythiophenes are generally more resistant to thermal degradation than their precursors. The precursor polymers all show a clear semi-crystalline behavior, with a decrease in crystallinity upon decreasing the number of regular 3-hexylthiophene units. On the other hand, the studied ionic (co)polythiophenes are fully amorphous. Changes in the counter ions have dramatic effects on the thermal properties. Bromine counter ions render the polymers strongly hygroscopic. The novel materials are of particular appeal in the field of organic photovoltaics, in which the imidazolium-substituted (co)polythiophenes can be beneficially applied as constituents of either active layers or electron transport layers. Their processability from green solvents is also of major importance for the field. © 2013 Elsevier Ltd. All rights reserved.

Stuyven B.,Catholic University of Leuven | Emmerich J.,Catholic University of Leuven | Eloy P.,Institute of Condensed Matter and Nanosciences IMCN | Van Humbeeck J.,Catholic University of Leuven | And 4 more authors.
Applied Catalysis A: General | Year: 2014

A peculiar effect was observed that the oxidation behavior of antimony oxide prepared in presence of a weak permanent magnetic field is changed. Reactivity of α-Sb2O3 (senarmontite) toward oxidation is significantly enhanced after recirculating its suspension in a magneto hydrodynamic (MHD) system. This inspired the MHD synthesis of a molybdenum-vanadium-antimony mixed oxide with superior catalytic activity for selective partial oxidation of isobutane. Traditionally these mixed oxides are synthesized via sol-gel processes involving complexing agents and/or costly alkoxides. Here a new convenient way is presented to synthesize Mo-V-Sb mixed oxide catalysts departing from senarmontite (α-Sb2O 3), ammonium heptamolybdate and ammonium vanadate. The MHD treated mixed oxide prepared from suspensions of Sb2O3 with Mo and V salts was evaluated in isobutane partial oxidation and compared with conventionally prepared catalysts. Improved performance was observed for MHD catalysts, with a peak methacrolein selectivity of 40% and decreased CO x selectivity as compared to a reference 'slurry-type' catalyst. Although the MHD synthesis mechanism cannot yet be explained on a molecular level, it represents significant scientific and economical potential. This report is intended as an invitation to assist in formulating a molecular mechanism capable of explaining these observations. © 2013 Elsevier B.V.

Lories X.,Institute of Condensed Matter and Nanosciences IMCN | Vandooren J.,Institute of Condensed Matter and Nanosciences IMCN | Peeters D.,Institute of Condensed Matter and Nanosciences IMCN
International Journal of Quantum Chemistry | Year: 2012

In this work, the isomerization mechanisms of dehydrofulvene radicals to the phenyl radical are described. This study shows, for 6-dehydrofulvene, a low-energy isomerization path going through a resonantly stabilized bicyclic system. In a second part, the different established mechanisms are applied to the closing of a second and third aromatic ring. This application highlights the possibility of forming new products, such as 2-naphthyl radical, and the effect of aromatic cycles on the new mechanisms. © 2011 Wiley Periodicals, Inc.

Emplit A.,Catholic University of Louvain | Tao F.F.,Institute of Condensed Matter and Nanosciences IMCN | Bailly C.,Institute of Condensed Matter and Nanosciences IMCN | Huynen I.,Catholic University of Louvain
European Microwave Week 2013, EuMW 2013 - Conference Proceedings; EuMC 2013: 43rd European Microwave Conference | Year: 2013

Nanocomposites absorbers with carbon nanotubes (CNTs) in solid polymer films are proposed for high EMI absorption performances. These conductive films exhibit a low permittivity at microwaves, which means a low reflection, with a high absorption capacity. Compared with usual solution based on foamed conductive composites, we indeed show that solid polymer films with two phases matrix and carbon nanotubes charges can be a great alternative to these foams. The two phases considered are polypropylene (PP) and poly[styrene-b- (ethylenealt-propylene)-b-styrene] (SEPS) copolymer. The electrical conductivity, the permittivity and EMI absorption are correlated with the quality of the dispersion. As a result of the low and constant permittivity of the obtained composite, the absorption performances are not limited by reflection mechanisms but fully controlled by the level of conductivity, fixed by the dispersion and weight content in CNTs. © 2013 European Microwave Association.

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