National Institute Of Materials Physics - Romania

Morphology is a key element in the functionality of low dimensional structures including here electroactive polymers, especially when applications such as muscle like actuators are sought. The reason is that morphology in the context of a high specific surface object strongly influences specific parameters such as ionic diffusion, conductivity and consequently the actuation capability of the system. In the present work a new architecture for microtube-based actuating elements is presented. Free-standing fibrillar microtubes with diameter in the range of micrometers and with a core-shell polyaniline/gold structure are fabricated through a scalable approach. Aligned electrospun poly(methyl methacrylate) fibers are coated with gold and are further employed as microstructured electrodes for the electrochemical deposition of polyaniline. Further the poly(methyl methacrylate) core was dissolved, leading to a tubular structure. The polyaniline/gold microtubes show complex, rapid and reversible movement patterns, with great stability and consistency over repeated actuation cycles. Thus, when the potential is swept between -0.2 and 1 V at different rates, the microtubes move, this movement being associated with the morphological and structural characteristics of the deposited polyaniline layer, a mechanism based on the expansion/contraction and conformational changes of the polymer chains due to the insertion/expulsion of ions. The response time of these electroactive microstructures during one cycle is in the range of seconds, a consequence of their low dimensionality and specific structure. Moreover the actuation takes place in different electrolytes including simulated gastric fluid, which enables a wide range of applications. (C) 2017 Elsevier B.V. All rights reserved.

The development of soft actuators by using inexpensive raw materials and straightforward fabrication techniques, aiming at creating and developing muscle like micromanipulators, represents an important challenge nowadays. Providing such devices with biomimetic qualities, for example, sensing different external stimuli, adds even more complexity to the task. We developed electroactive polymer coated microribbons that undergo conformational changes in response to external physical and chemical parameters. These were prepared following three simple steps. During the first step nylon-6/6 microribbons were fabricated by electrospinning. In a second step the microribbons were one side coated with a metallic layer. Finally, a conducting layer of polypyrrole was added by means of electrochemical deposition. Strips of polypyrrole-coated aligned microribbon meshes were tested as actuators responding to current, pH, and temperature. The electrochemical activity of the microstructured actuators was investigated by recording cyclic voltammograms. Chronopontentiograms for specific current, pH, and temperature values were obtained in electrolytes with different compositions. It was shown that, upon variation of the external stimulus, the actuator undergoes conformational changes due to the reduction processes of the polypyrrole layer. The ability of the actuator to hold and release thin wires, and to collect polystyrene microspheres from the bottom of the electrochemical cell, was also investigated.

For DEMO fusion reactor an expected heat flux of about 10MW/m(2) should be extracted by the divertor which will have, most likely, an armour part made of W and a following heat sink part made of Cu, or ODS Cu alloy. Unfortunately, for these materials the optimum operating temperature windows do not overlap. Thermal barrier materials are interface materials included in such components, aiming to keep the temperatures of both armour and heat sink parts in the corresponding operating windows, and to mitigate the effects of their different thermomechanical properties. Here we propose a simple spark plasma sintering route to create Cu-based composites with a high content (10-40 vol%) of various dispersed materials (Al or Y oxides, C, SiC), allowing a fine tuning of the content and a large pool of predefined shapes and dimensions. The resulting specimens can be further joined to armour and heatsink components via a similar electrical field assisted technology. Micro-structural and thermal properties are investigated for these materials allowing to select the most suited materials in view of their thermal conductivity and thermal expansion coefficients. (C) 2017 The Authors. Published by Elsevier B.V.

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.

In this study, coatings based on lysozyme embedded into a matrix of polyethylene glycol (PEG) and polycaprolactone (PCL) were fabricated by two different methods (Matrix Assisted Pulsed Laser Evaporation -MAPLE and Dip Coating) for obtaining antimicrobial coatings envisaged for long term medical applications. Coatings with different PEG: PCL compositions (3: 1; 1: 1; 1: 3) were synthesized in order to evaluate the antimicrobial activity of lysozyme embedded into the polymeric matrix. The main surface features, such as roughness and wettability, with impact on the microbial adhesion as well as on the eukaryote cell function were measured. The obtained composite coatings exhibited a significant antibacterial activity against Escherichia coli, Bacillus subtilis, Enterococcus faecalis and Staphylococcus aureus strains. As well, specific blended coatings showed appropriate viability, good spreading and normal cell morphology of SaOs2 human osteoblasts and mesenchymal stem cells (MSCs). These investigations highlight the suitability of biodegradable composites as implant coatings for decreasing the risk of bacterial contamination associated with prosthetic procedures. (C) 2016 Elsevier B.V. All rights reserved.

Mixed layers of azomethine oligomers containing 2,5-diamino-3,4-dicyanothiophene as central unit and triphenylamine (LV5) or carbazol (LV4) at both ends as donor and fullerene derivative, [6,6]-phenylC61 butyric acid butyl ester ([C60] PCB-C4) as acceptor, have been prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) on glass/ITO and Si substrates. The effect of weight ratio between donor and acceptor (1: 1; 1: 2) and solvent type (chloroform, dimethylsulphoxide) on the optical (UV-vis transmission/absorption, photoluminescence) and morphological properties of LV4 (LV5): [C60] PCB-C4 mixed layers has been evidenced. Dark and under illumination I-V characteristics of the heterostructures realized with these mixed layers sandwiched between ITO and Al electrodes have revealed a solar cell behavior for the heterostructures prepared with both LV4 and LV5 using chloroform as matrix solvent. The solar cell structure realized with oligomer LV5, glass/ITO/LV5: [C60] PCB-C4 (1: 1) has shown the best parameters. (C) 2017 Elsevier B.V. All rights reserved.

Organic heterostructures based on poly(3-hexylthiophene) (P3HT) and fullerene (C60) as blends or multilayer were deposited on Al:ZnO (AZO) by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The AZO layers were obtained by Pulsed Laser Deposition (PLD) on glass substrate, the high quality of the films being reflected by the calculated figure of merit. The organic heterostructures were investigated from morphological, optical and electrical point of view by atomic force microscopy (AFM), UV-vis spectroscopy, photoluminescence (PL) and current-voltage (I-V) measurements, respectively. The increase of the C60 content in the blend heterostructure has as result a high roughness. Compared with the multilayer heterostructure, those based on blends present an improvement in the electrical properties. Under illumination, the highest current value was recorded for the heterostructure based on the blend with the higher C60 amount. The obtained results showed that MAPLE is a useful technique for the deposition of the organic heterostructures on AZO as transparent conductor electrode. (C) 2017 Elsevier B.V. All rights reserved.

Dielectric measurements of bismuth germanate oxides reveal significant changes in the amorphous phase, between 200 and 350 degrees C, where the crystallisation processes start below the glass transition temperature. The capacitive and loss measurements versus temperature and frequency suggest an incipient glass transition below 350 degrees C associated with an increase in the clusters, mainly those formed by GeO4 tetrahedra, responsible for the dipolar orientation effects. An increase in the capacitive parameter versus temperature at lower frequencies, especially over 250 degrees C has been associated with the increase in mobility of the clusters. The physical meaning of those processes has been associated with the formation of a highly viscous layer enriched in GeO4 which is formed during crystallisation. This layer acts as a diffusion barrier and hinders further crystal growth. A higher frequency is required in the crystallisation processes to compensate for the thermal disorder in the amorphous materials. The crystallisation process is identified by the decrease in the dielectric constant despite the increase in temperature.

The crystallization mechanism of sol-gel-derived NaYF4:(Yb, Er) up-converting phosphors has been studied by differential scanning calorimetry analysis using both model-free and model fitting approaches. Structural and optical data have shown that the hexagonal NaYF4:(Yb, Er) phase crystallization process occurs at around 315 degrees C as a result of the thermal decomposition of the metal trifluoroacetates. As the annealing temperature increases, sphere-like microcrystals of about 1-2 mu m size (at 300 degrees C) break up into smaller ones (400-500 nm size) and finally collapse at higher temperatures (600 degrees C); the up-conversion luminescence signal intensity increases due to the crystallinity improvement and dehydration process. The crystallization process can be described as an autocatalytic-type reaction where the accompanying cubic NaYF4 phase played a catalytic role by reducing the energy barrier against the crystallization of the hexagonal NaYF4 phase, causing its fast self-accelerated crystallization. The energy resulting from the disintegration process of the initial NaYF4 microcrystals contributed to the growth and agglomeration processes and finally the collapse of the crystalline fragments with increasing temperature.

We report the synthesis of tungsten nanoparticles with two distinct shapes, concave hexapods and faceted cube-octahedral nanocrystals. These types of nanoparticles were obtained with a cluster source based on magnetron sputtering and gas aggregation, by supplying the magnetron discharge with continuous or pulsed wave radiofrequency power. Detailed morphological and microstructural studies were performed. The hexapod particles present a dendritic growth while the faceted ones have a single crystal structure. The alpha-W and beta-w crystalline phases are present in both types of nanoparticles; nevertheless, the beta-W structure is dominant for the hexapod ones. Although the beta-w phase is usually metastable, we observed its unexpected long term preservation in hexapod nanoparticles. The results, added to previously reported nanoflower-like particles, point out the ability to control the shape and structure of the tungsten nanoparticles using the magnetron sputtering gas aggregation technique. (C) 2017 Elsevier B.V. All rights reserved.