National Institute Of Materials Physics - Romania

Nanocomposites have been obtained by dispersing various amounts of vapor grown carbon nanofibers within isotactic polypropylene. Thermal investigations done by differential scanning calorimetry and dynamic mechanical analysis revealed the effect of the vapor grown carbon nanofibers on the melting, crystallization, alpha, and beta relaxations. Direct current electrical features of these nanocomposites have been investigated and related to the thermal features of these nanocomposites. The effect of the loading with carbon nanofibers on the electrical properties of these nanocomposites is discussed within the percolation theory. The percolation threshold was estimated at about 5.5% wt carbon nanofibers. The temperature dependence of the direct current conductivity is analyzed in detail and it is concluded that the electronic hopping is the dominant transport mechanism. A transition from one-dimensional hopping towards a three-dimensional hopping was noticed as the concentration of carbon nanofibers was increased from 10% wt to 20% wt carbon nano-fiber. The possibility of a differential negative resistivity is suggested. (C) 2017 Wiley Periodicals, Inc.

A series of flexibly linked bis-imidazolium salts with alkyl sulfate anions having different chain lengths (10, 12, 14) was designed and prepared starting from 1,1'-(alpha,omega-alkanediyl)-bisimidazole and alkyl bromides (14 or 16 carbon atoms) followed by metathesis with the corresponding sodium salts. These compounds were investigated because of their liquid crystalline properties using a combination of differential scanning calorimetry (DSC), polarized optical microscopy (POM) and temperature dependent powder X-ray diffraction (XRD). All nine bis-imidazolium compounds with alkyl sulfate anions show liquid crystalline properties which were influenced by flexible spacer length, alkyl tail length and, finally, the length of alkyl chains attached to sulfate groups. Broader mesophase ranges were found for compounds with a shorter spacer (six carbon atoms), about 70 degrees C. For compounds with a spacer of ten carbon atoms, higher mesophase ranges and clearing temperatures were found for longer alkyl tails (sixteen carbon atoms). Increasing the length of alkyl chains attached to sulfate anions resulted in higher clearing temperatures for compounds with the longer spacer. The variation in the carbon atom number of the alkyl sulfate anion for bis-imidazolium compounds with the shorter spacer has almost no impact on their SmA phase stability.

The "one-pot" hydrolyltic hydrogenation of cellulose towards C2-C6 sugar alcohols has been recognized as one of the most promising biomass valorization routes for the production of high added-value chemicals. In this work, we studied the performance of Ru and Pt catalysts supported on micro/mesoporous activated carbon, in the hydrolytic hydrogenation of microcrystalline and ball-milled cellulose, in neat water, at 180 C and at relatively low hydrogen pressure of 2 MPa. The impact of metal loading (1-5 wt.%), metal reduction method (H2 at 350 C or NaBH4) and acidification (sulfonation) of the AC support on cellulose conversion and selectivity to the various products were systematically addressed. It was shown that Pt is significantly more selective towards hexitols (sorbitol and mannitol) compared to Ru, in glucose rich reaction media, such as those offered by the easily hydrolyzed ball-milled cellulose. For example, the 5wt%PtIAC-SO3H catalyst afforded hexitols yield of 69.5 wt.% (at 96.1% conversion) compared to 10.9 wt.% (at 95.2% wt.% conversion) obtained by the corresponding Ru catalyst, the latter being also selective towards glycerol and propane-1,2-diol (propylene glycol). A relatively moderate metal loading, such as in 3 wt.%Ru/AC-SO3H, was more favorable for hexitols production (44.5 wt.% yield, at 94.8 wt.% conversion) with Ru catalysts. These results were also verified by glucose hydrogenation experiments that were conducted at the same experimental conditions. Both Pt and Ru exhibited relatively high glucose hydrogenation activity towards hexitols, versus retro-aldol reactions that lead directly to smaller C2-C4 compounds, while the difference in the final product yields between the two metals was attributed to the higher hexitols hydrogenolysis (C C cleavage) reactivity of Ru. HRTEM data showed the formation of metallic crystalline Pt and Ru nanoparticles (<= 4 nm, depending on loading) as well as of amorphous oxygen-rich M(O)(x)(delta+) phases, which were also confirmed by the XPS data. The presence of these phases which may be a source of acidity, as well as the bacisity of the parent AC used in this study, were mainly responsible for inducing isomerization, retro-aldol and dehydration reactions leading eventually to increased glycerol and propylene glycol selectivity, as was observed for both low-metal catalysts, i.e. 1 wt.% Pt or Ru/AC. (C) 2017 Elsevier B.V. All rights reserved.

A novel nanocomposite was obtained through the covalent immobilization of lipoic acid on the surface of silver nanoparticles-decorated silica nanoparticles (SiO2@Ag). The hybrid organic inorganic material obtained was characterized by Fourier transform infrared spectroscopy, thermal analysis, scanning and transmision electron microscopy, X-ray photoelectron spectroscopy and UV-Visible spectroscopy. Its antioxidant, cytotoxic, antimicrobial activity and influence on mammalian cells cycle were evaluated. The results of this study have shown that the functionalization of SiO2@Ag with lipoic acid resulted in a composite with increased specificity of interaction with different mammalian cell lines and antioxidant activity, but with decreased cytotoxicity and antimicrobial properties. Therefore, the SiO2@Ag functionalized with lipoic acid could be successfully used in certain concentrations to modulate the cell cycle, in order to obtain the desired anti-proliferative or stimulatory therapeutic effect. (C) 2017 Elsevier B.V. All rights reserved.

Pulsed Laser Deposition (PLD) and Matrix Assisted Pulsed Laser Evaporation (MAPLE) techniques were applied for growing hydroxyapatite (HA) thin films on titanium substrates. All experiments were conducted in a reaction chamber using a KrP* excimer laser source (lambda = 248 nm, TEWHM approximate to 25 ns). Half of the samples were post-deposition thermally treated at 500 degrees C in a flux of water vapours in order to restore crystallinity and improve adherence. Coating surface morphologies and topographies specific to the deposition method were evidenced by scanning electron, atomic force microscopy investigations and profilometry. They were shown to depend on deposition technique and also on the post-deposition treatment. Crystalline structure of the coatings evaluated by X-ray diffraction was improved after thermal treatment. Biocompatibility of coatings, cellular adhesion, proliferation and differentiation tests were conducted using human mesenchymal stem cells (MSCs). Results showed that annealed MAPLE deposited HA coatings were supporting MSCs proliferation, while annealed PLD obtained films were stimulating osteogenic differentiation. (C) 2016 Elsevier B.V. All rights reserved.

High purity Zinc Selenide (ZnSe) crystals are produced starting from elemental Zn and Se to be used for the search of the neutrinoless double beta decay (0vDBD) of Se-82. In order to increase the number of emitting nuclides, enriched Se-82 is used. Dedicated production lines for the synthesis and conditioning of the (ZnSe)-Se-82 powder in order to make it suitable for crystal growth were assembled compliant with radiopurity constraints specific to rare event physics experiments. Besides routine check of impurities concentration, high sensitivity measurements are made for radio-isotope concentrations in raw materials, reactants, consumables, ancillaries and intermediary products used for ZnSe crystals production. Indications are given on the crystals perfection and how it is achieved. Since very expensive isotopically enriched material (Se-82) is used, a special attention is given for acquiring the maximum yield in the mass balance of all production stages. Production and certification protocols are presented and resulting ready-to-use (ZnSe)-Se-82 crystals are described. (C) 2017 Elsevier B. V. All rights reserved.

Bi1.5-xZn0.92-yNb1.5O6.92-delta (BZN) thin films were grown by pulsed laser deposition on two different Pt-covered substrates, namely textured {111} Pt/TiO2/SiO2/(100) Si substrate (Pt/Si) and epitaxial {111} Pt/R-plane sapphire substrate (Pt/sapphire). In both cases, the BZN films present {111} and {100} out-of-plane orientations, in relative ratios of 65: 35 on Pt/Si and 80: 20 on Pt/sapphire, respectively. The film grown on Pt/Si is textured, while the film deposited on Pt/sapphire presents epitaxial-like relationships with the substrate, for both out-of-plane orientations. Dielectric measurements were taken on both types of thin films, using Pt/BZN/Pt planar capacitor structures. The BZN/Pt/sapphire film presents higher dielectric constant (245 at 100 kHz) and higher tunability (12% at 600 kV/cm) than the BZN/Pt/Si film (200; 6%), while the dielectric losses values are nearly same (similar to 0.05).

Lowering the temperature of crystallization by deposition of thin films on a heated substrate represents the easiest way to find new means to develop and improve new working devices based on nanocrystals embedded in thin films. The improvements are strongly related with the increasing of operation speed, substantially decreasing the energy consumption and reducing unit fabrication costs of the respective semiconductor devices. This approach avoids major problems, such as those related to diffusion or difficulties in controlling nanocrystallites size, which appear during thermal treatments at high temperatures after deposition. This article reports on a significant progress given by structuring Ge nanocrystals (Ge-NCs) embedded in silicon dioxide (SiO2) thin films by heating the substrate at 400 degrees C during co-deposition of Ge and SiO2 by magnetron sputtering. As a proof-of-concept, a Si/Ge-NCs:SiO2 photo-sensitive structure was fabricated thereof and characterized. The structure shows superior performance on broad operation bandwidth from visible to near-infrared, as strong rectification properties in dark, significant current rise in the inversion mode when illuminated, high responsivity, high photo-detectivity of 10(14) Jones, quick response and significant conversion efficiency with peak value reaching 850% at -1 V and about 1000 nm. This simple preparation approach brings an important contribution to the effort of structuring Ge nanocrystallites in SiO2 thin films at a lower temperature for the purpose of using these materials for devices in optoelectronics, solar cells and electronics on flexible substrates.

Hydroxyapatite is a calcium phosphate intensively proposed as a bone substitution material because of its resemblance to the constituents of minerals present in natural bone. Since hydroxyapatite's properties are mainly adequate for nonload bearing applications, different solutions are being tested for improving these properties and upgrading them near the target values of natural bone. On the other hand, starch (a natural and biodegradable polymer) and its blends with other polymers have been proposed as constituents in hydroxyapatite mixtures due to the adhesive, gelling, and swelling abilities of starch particles, useful in preparing well dispersed suspensions and consolidated ceramic bodies. This article presents the perspectives of incorporating starch and starch blends in hydroxyapatite materials. Based on the role of starch within the materials, the review covers its use as (i) a polymeric matrix in hydroxyapatite composites used as adhesives, bone cements, bone waxes, drug-delivery devices or scaffolds and (ii) a sacrificial binder for fabrication of porous hydroxyapatite scaffolds. The suitability of these materials for bone reconstruction has becomes a reachable aim considering the recent advancements in ceramic fabrication and the current possibilities of controlling the processing parameters.

A new family of cyclometalated palladium(II) complexes with the non-symmetric dimeric liquid crystal Schiff base alpha-(4-cyanobipheny1-4'-yloxy)-omega-(4-n-decyloxyanilinebenzylidene-4'-oxy) hexane and alkoxysubstituted N-benzoyl thiourea (BTU) derivatives as auxiliary ligands was designed and prepared with the aim to study the influence of increasing the number of aliphatic chains on the molecular organization in the liquid crystal phase. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction. A transition from the lamellar (complex 3a with two aliphatic chains on BTU ligand) to columnar organization (complexes 3b and 3c having three and four chains on BTU ligand, respectively) was evidenced for these palladium(II) complexes, which was correlated with the increase of the number of terminal chains at molecular periphery. (C) 2017 Elsevier B.V. All rights reserved.