Showing papers in "Materials today communications in 2017"

Three-dimensional printing of highly conductive polymer nanocomposites for EMI shielding applications

Abstract: Here we applied three-dimensional (3D) printing of conductive microstructures for the functional optimization of lightweight and semi-transparent electromagnetic interference (EMI) shields. Highly conductive 3D printable inks with electrical conductivities up to ∼5000 S m−1 were fabricated from carbon nanotubes/polylactic acid (CNT/PLA) nanocomposites. Solvent-cast 3D printing enabled us to fabricate conductive scaffold microstructures and investigate the influence of various important structural parameters (i.e., inter-filament spacing, number of layers and printing patterns) on their transparency and EMI shielding effectiveness. The results revealed a significant improvement of the specific EMI shielding effectiveness of CNT/PLA nanocomposites printed as 3D scaffolds compared to CNT/PLA hot-pressed in solid forms (∼70 vs ∼37 dB g−1 cm3). The transparency of the scaffolds could vary from ∼0% to ∼75% by modifying their printing patterns and inter-filament spacing. To the best of our knowledge the conductivity of the fabricated ink is the highest among the other reported 3D printable polymer composite inks and this is the first reported systematic study on EMI shielding using a 3D printing technique. These results are highly beneficial for the fabrication and structural optimization of EMI shields where light and/or transparent structures are advantageous, such as in aerospace systems, portable electronic devices or smart fabrics.

Micro-nanostructured polymer surfaces using injection molding: A review

Abstract: Micro injection molding is in great demand due to its efficiency and applicability for industry. Polymer surfaces having micro-nanostructures can be produced using injection molding. However, it is not as straightforward as scaling-up of conventional injection molding. The paper is organized based on three main technical areas: mold inserts, processing parameters, and demolding. An accurate set of processing parameters is required to achieve precise micro injection molding. This review provides a comparative description of the influence of processing parameters on the quality of final parts and the precision of final product dimensions in both thermoplastic polymers and rubber materials. It also highlights the key parameters to attain a high quality micro-nanostructured polymer and addresses the contradictory effects of these parameters on the final result. Moreover, since the produced part should be properly demolded to possess a high quality textured polymer, various demolding techniques are assessed in this review as well.

Drug delivery systems for prolonged duration local anesthesia

Abstract: Numerous drug delivery systems have been applied to the problem of providing prolonged duration local anesthesia (PDLA). Here we review the rationale for PDLA, the desirable features for and important attributes of such systems, and specific examples that have been developed.

Tunable (violet to green) emission by high-yield graphene quantum dots and exploiting its unique properties towards sun-light-driven photocatalysis and supercapacitor electrode materials

Abstract: The precise control of dimension and mono-dispersibility of graphene quantum dots (GQDs) is still a challenge and new developments in this field are of great interest for scientific community. In this work, we have investigated the feasibility of the production of mono-dispersed spherical GQDs (∼4 nm) based on a treatment solely with ammonia solution as both, reducing and stabilizing agent. The structure, size and shape of the so synthesized GQDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy measurements. The synthesized GQDs show excitation-dependent tunable color emission (violet to green). These GQDs could be potentially used as biomarkers for florescent bioimaging. The GQDs also prove to be excellent sunlight-driven photocatalysts for the photodegradation (45%) of methylene blue (MB) dye. Therefore, these GQDs could find remarkable application in the field of photocatalysis. Electrochemical measurements indicate good rate capability and stability of the GQDs in view of their use as supercapacitor electrode material. The present work not only provides a better explanation of the experimental observations, but also suggests an efficient method for the controllable synthesis of multi-functional GQDs.

Innovative composites and hybrid materials for electric vehicles lightweight design in a sustainability perspective

Abstract: Lightweight design and electrified powertrain have become important strategies in the automotive industry to reduce fuel demand and break down emissions respectively. Lightweighting of Electric Vehicles (EVs) is considered a step forward because advantages of both EVs and lightweight design could be combined to reduce environmental impacts even further. This paper would contribute to the advancement of knowledge in this field and it deals with the environmental analysis, by means of Life Cycle Assessment (LCA), of composite-based and hybrid material lightweight solutions for EVs modules in comparison with the corresponding reference ones, by assuming no changes in the powertrain system (e.g. battery resizing). Particular attention is given to primary data collection to build the environmental eco-profiles of four innovative composites. Then, a four-level approach to interpret LCA outcomes in a clear and comprehensive way is proposed in this paper. Despite the relevant mass reduction, environmental benefits are not registered for all the analysed solutions, and the main reason is the large impact from the production stage of the new materials, raw materials particularly. Outcomes from this paper showed that Abiotic Depletion Potential (ADPel.) generally had a different trend if compared to Global Warming Potential (GWP) and Primary Energy Demand (PED) so their evaluation in parallel is recommended. Overall, the innovative materials that have a high impact in the production stage could not be suitable in the case of EVs where the emission rate in the use stage is lower than the one of traditional vehicle, so a different application should be also evaluated.

Nucleation effect of unmodified graphene nanoplatelets on PVDF/GNP film composites

Abstract: Development of polyvinylidene fluoride (PVDF) film composite filled with carbon-based nanomaterials is attracting considerable attention in engineering applications. Numerous studies focus on the enhancement of PVDF properties by adding chemically modified graphene oxide or functionalized carbon nanotubes, or by modifying the polymer chains. On the other hand, in this paper we investigate the nucleation effect of graphene nanoplatelets (GNPs) on morphology and structure of PVDF, without any chemical modification or functionalization either of the GNPs or of the polymer chains. Thus, we fabricate GNP-filled PVDF composite films by the solution casting method. Then, we investigate the effect of GNPs on composite porosity, crystallinity and polymer phases, with special emphasis on the formation of β -phase. To this purpose, the produced PVDF/GNP composite films are characterized through scanning electron microscopy and atomic force microscopy topographies, differential scanning calorimetry, X-ray powder diffraction and Fourier transform infrared spectroscopy. All these experimental characterizations show that GNPs uniformly dispersed in PVDF, without any modification or functionalization, influence significantly the polymer structure and porosity, enhancing the β -phase crystals formation. Finally, the electrical, mechanical and electromechanical properties of the produced PVDF/GNP composite films are characterized.

Cyclomatrix polyphosphazenes frameworks (Cyclo-POPs) and the related nanomaterials : synthesis, assembly and functionalisation

Abstract: Poly (organophosphazene) (POP) is one of the most important inorganic polymers along with polysiloxane. The versatile phosphazene chemistry enables a wealth of functional inorganic-organic hybrid polymers with P N structures ranging from covalently crosslinked cyclomatrix phosphazene to linear POP copolymers. Cyclomatrix polyphosphazene framework materials (Cyclo-POPs) represent a novel type of molecular composites, and can be facilely formed via a rapid one-step polycondenzation and simultaneous self-assembly process under ambient conditions, and the stereoscopic morphologies are tuneable from zero-dimension (0D) to 3D depending on the compositions and reaction conditions. The novel cyclo-POPs have shown distinctive advantages over boron-containing covalent organic framework (COFs) materials in terms of the facile and rapid synthesis and integrated functionalities. Moreover, the highly crosslinked P N− backbone structures are readily to be transformed into porous carbon nanomaterials with intrinsically doped heteroatoms (P, N, S, O, B, depending on the framework skeletons), which are desirable for catalysis, sensors and energy storage applications. In this article, we critically overview the rational design, synthesis and functionalisation of the cyclo-POPs materials, and their emerging applications in optoelectronics, catalysis, adsorption and energy storage devices, along with the technical challenges and development perspectives.

In-situ direct grafting of graphene quantum dots onto carbon fibre by low temperature chemical synthesis for high performance flexible fabric supercapacitor

Abstract: A novel chemical synthesis method has been developed to directly graft graphene quantum dots (GQDs) onto carbon fibre (CF) in-situ via covalent ester linkages at low temperature (90 °C). SEM and TEM images depict the grafting of GQDs on CF showing about 75% of the GQD falls below 40 nm. The grafting was further confirmed by FTIR, RAMAN, XPS and XRD spectroscopy. The flexible fabric supercapacitor manufactured using the grafted materials shows increased electrochemical capacitance (about 5.5 times) than that of CF by providing active surface sites of GQDs, creating defects on the surface and preventing GQD recombination. This supercapacitor maintained approximately 97% of its initial capacitance after 5000 cycles at 2 A g−1 current density, suggesting a stable performance of the supercapacitor and holds a promising potential in the field of advanced flexible electronic devices.

Influence of surface metallic silver deposit and surface fluorination on the photocatalytic activity of rutile TiO2 for the degradation of crystal violet a cationic dye under UV light irradiation

Abstract: Silver metallization and fluorination on the surface of rutile TiO2 (SRT and FRT) was carried out by photochemical reduction and wet impregnation methods respectively. TiO2, SRT and FRT were characterized by various analytical techniques like PXRD, SEM, EDX, FTIR, PL, UV–vis absorbance and XPS. The photocatalytic degradation of crystal violet (CV) was carried out at three different pH conditions. Acidic pH was found to be more favorable for the degradation, in spite of low adsorption of cationic CV molecules on the catalyst surface. The electrostatic repulsion at this pH drives the CV molecules into the bulk of the solution suggesting the involvement of bulk hydroxyl radicals rather than surface adsorbed hydroxyl radicals. The degradation efficiency can be represented by the following order SRT > FRT > TiO2. The Ti-peroxo (Ti-OO-Ti) complex species formed in presence of H2O2 by the combination of two trapped holes (Ti–O ) in aqueous medium is predicted to enhance the rate of generation of hydroxyl radicals. The exciton mobility is dependent on the polaron effective mass which is higher for rutile TiO2 accounting for its lower activity. The bulk charge carrier transport which is less in bare rutile TiO2 is enhanced in the surface modified TiO2. Effective trapping of photogenerated excitons/electrons by F-/Ag0 can facilitate their migration and increase the activity by tenfolds. The rate of degradation of CV followed two reaction pathways, slower N-demethylation in basic conditions and rapid aromatic cleavage at the central carbon atom in the acidic pH conditions.

Synthesis of polyaniline/α-Fe2O3 nanocomposite electrode material for supercapacitor applications

Abstract: Polyaniline/Ferric oxide (PANI/α-Fe2O3) nanocomposites were synthesized via a simple precipitation of FeCl3 using NH4OH as the precipitating agent, followed by in situ polymerization of aniline. PXRD pattern of as-synthesized nanocomposites showed characteristic peaks of α-Fe2O3 in the PANI matrix. Structural and morphological characterization confirmed the encapsulation of α-Fe2O3 nanoparticles in PANI matrix to form PANI/α-Fe2O3 nanostructures. PANI/α-Fe2O3 as an electrode material for supercapacitor exhibited a maximum specific capacitance of 974 Fg−1 at a scan rate of 2 mVs−1 using CV and Csp of 857 Fg−1 at a current density of 0.2 Ag−1 using CP. Further, the material also exhibited a high energy density of 118 Wh kg−1 with a maximum power density of 9.8 kW kg−1 and an excellent cyclic stability with capacitance retention of about 94% after 2000 cycles. These superior electrochemical results over bare PANI and α-Fe2O3 shows the PANI/α-Fe2O3 nanocomposites to be promising electrode material for high performance energy storage systems.

Rapid and low temperature processing of mesoporous TiO2 for perovskite solar cells on flexible and rigid substrates

Abstract: Perovskite solar cells (PSCs) have recently attracted the attention of the scientific community because of the rapid advances in their development. Most of the state-of-the-art devices contain mesoporous titanium dioxide (TiO2) as an electron transport layer. The drawback of such TiO2 layers is that it often needs high temperature sintering at 450–500 °C for 30 min, which slows down the fabrication process and is clearly not compatible with future roll-to-roll (R2R) manufacturing. The aim of this study was to develop low temperature and rapid curing techniques for mesoporous TiO2 thin films, which are compatible with R2R processing and heat-sensitive plastic substrates for PSCs. Several alternative annealing techniques were tested on rigid and flexible substrates, such as UV-ozone (UV/O3) treatment, oxygen plasma treatment (O2 plasma) and Intense Pulsed Light (IPL) sintering and compared to conventional thermal annealing. After each treatment, the mesoporous layers were characterized using Raman spectroscopy, UV–vis spectroscopy, thermogravimetric analysis and scanning electron microscopy. Low temperature sintering techniques were specifically optimized for the mesoporous TiO2 layers and were adapted for the fabrication of PSCs. Sintering process and solar cells manufacturing were optimized for two different device architectures on glass as well as on polyethylene naphthalate (PEN) substrates. Moreover, the maximum temperature of the mesoporous TiO2 layer during the IPL curing process was simulated to better understand the curing process. By employing IPL curing, the processing time for the mesoporous TiO2 layer can be reduced from 30 min to a few seconds without significant loss in the device performance. In particular stabilized PCE of 16% and 12% were obtained using IPL on glass and PEN substrates respectively. This processing route paves the way for future low temperature R2R processing of mesoscopic PSC on plastic substrates.

Effect of Al and Mo addition on phase formation, mechanical and microstructure properties of spark plasma sintered iron alloy

Abstract: The effect of aluminum (Al) and molebdenium (Mo) addition on the phase formation and final properties of iron based alloys has been investigated by powder metallurgy route and spark plasma sintering process. Compounds containing iron (Fe)- 5 wt% Al, Fe-5 wt% Mo and Fe-5 wt% Al and 5 wt% Mo were prepared using a high-energy mixer after milling for 10 min. In order to achieve maximum displacement, the sintering process was performed in the temperature range of 600–650 °C. Furthermore, the sintered samples were annealed at 1100 °C for 2 h in argon atmosphere. The obtained results indicated that all samples reached to a high enough density at low sintering temperatures and when sintering was performed at high temperatures, the partial melting occurred. The XRD and FESEM investigations revealed the formation of FeMo and AlFe intermetallic and solid solution phases when both Al and Mo additives were used together. Fe-5 wt% Mo-5 wt% Al sample obtained the maximum bending strength (730 ± 31 MPa) and hardness (530 ± 27 Vickers) after sintering at temperature of 630 °C.

Design and synthesis of CeO2 nanowire/MnO2 nanosheet heterogeneous structure for enhanced catalytic properties

Abstract: A novel CeO2 nanowires/MnO2 nanosheets heterogeneous structure was successfully synthesized by a facile hydrothermal method and its carbon monoxide (CO) catalytic properties were studied. Amorphous MnO2 nanosheets were firstly formed on the surface of CeO2 nanowires to establish a core-shell structure mediated by interfacial redox process which was further transformed to δ-MnO2 through post heat treatment. Compared with as-prepared CeO2 nanowires, CeO2 nanowires/MnO2 nanosheets heterogeneous architecture showed improved catalytic performance because of the strong synergistic interaction between CeO2 and MnO2 at the interface. Moreover, the formation of δ-MnO2 further enhanced the catalytic properties by achieving more defective structures through a slight Mn doping. The catalytic activities can be further enhanced by core-shell compositional optimization. Thus, designing heterogeneous junction was an attractive approach for improving the catalytic properties of CeO2 based nanomaterials.

Alternative designs of load−sharing cobalt chromium graded femoral stems

Abstract: The incapability of controlling relative micromotions and load transfers to a peri-prosthetic femur shortens implant longevity This study aims to evaluate the possibility of applying graded porous cobalt chromium (CoCr) to cementless femoral stems 3D finite element analyses and physical testings of hip implants were conducted with four different grading orientations, along the axial and radial planes of the femoral stem The results show that the CoCr graded femoral stems with a porosity decreased caudally and inwardly may control the relative micromotions in an acceptable range for bone ingrowth, significantly increase stress transfers on the Gruen zone 1 and 7, and attain the flexural stiffness comparable to human femurs Therefore, CoCr graded femoral stems demonstrate great potential for applications in implants with reduced stress shielding and improved long-term survival rates

Weathering degradation performance of PLA and its glass fiber reinforced composite

Abstract: The objective of this study was to explore the degree of improvement in the resistance of biodegradable polylactide (PLA) structure against atmospheric weathering (outdoor) conditions when reinforced with only 15 wt% E-glass fibers (GF). For this purpose, both neat PLA and PLA/GF composite specimens were exposed to accelerated weathering conditions of both UV-irradiation and moisture cycles in accordance with ISO 4892-3 standards for various periods until 400 h. Many characterization techniques used revealed that the alterations in the structure and properties of the specimens were due to the drastic decrease in the molecular weight of the PLA matrices via chain scission reactions. It was observed that reductions in the mechanical properties (strength-modulus-toughness) of the neat PLA were much more critical compared to the reductions in the PLA/GF composite. For instance, the reduction in the tensile strength of the neat PLA specimen was as much as 92%; while that reduction for the PLA/GF specimen was only 34%. Because, inorganic strong glass structure of the GF reinforcements having almost no chemical degradation during weathering periods kept their actions in the composite strengthening-stiffening-toughening mechanisms.

An investigation of growth mechanism of coal derived graphene films

Abstract: The growth mechanism of coal derived graphene films synthesized via chemical vapor deposition on copper substrates was investigated utilizing Raman spectroscopy, X-ray photoelectron spectroscopy, selected area electron diffraction, optical microscopy, and gas chromatography. The synthesis of coal derived graphene films is a two-step process, wherein the copper in annealed followed by flash pyrolysis of coal under hydrogen environment. The growth mechanism involves a copper catalyzed reaction to produce a carbon film within the first few minutes of synthesis, followed by a hydrogen catalyzed graphitization of the underlying carbon film to form graphene domains which merge together to form graphene films.

Insulation material production from onion skin and peanut shell fibres, fly ash, pumice, perlite, barite, cement and gypsum

Abstract: This study examines the suitability of fly ash, pumice, perlite, barite, cement and gypsum along with onion skin and peanut shell fibers as an insulating material. Apparent specific gravities, water absorption rates, flexure and compressive strengths of the prepared samples were determined. Moreover, thermal conductivity, ultrasonic sound penetration coefficient and radioactive relative permeability values were, also, investigated. The latter three properties of the samples produced with barite, pumice, perlite, onion skins and peanut shells were observed to be low. Consequently, this composite can be used in various situations because of its improved thermal conductivity feature, especially, as coating material in offices which are exposed to radiation a lot. Moreover, it can, also, be used for the radiation insulation of the walls of the radiation units of hospitals.

Disulfide bonds and metal-ligand co-crosslinked network with improved mechanical and self-healing properties

Abstract: The simultaneous improvement of mechanical properties and healing efficiency of self-healing polymers is often contradictory because of the different requirements of chain mobility for these two demands. In this study, we have incorporated imidazole-zinc ion coordination bonds into a disulfide based cross-linked network to investigate the influence of non-covalent bonds on the mechanical properties and healing efficiency of dynamic covalent network. It is found that the modulus, strength, and toughness of covalent network were greatly improved by the introduction of non-covalent bonds due to the additional cross-linking and energy dissipation functions of non-covalent bonds. While the time dependent healing test revealed the higher healing efficiency of covalent network by the addition of non-covalent bonds because of their faster exchange dynamics as compared to dynamic covalent bonds. The co-crosslinked network can also be reprocessed by hot press due to the dynamic nature of both covalent and non-covalent crosslinkings.

Generation and evolution mechanisms of pavement asphalt aging based on variations in surface structure and micromechanical characteristics with AFM

Abstract: Asphalt aging is more serious at the pavement surface due to the exposed environment, which can cause to the variations of surface characteristics. However, the surface characteristics were lost in reshaping the asphalt sample when applying the traditional aging method. It is still unclear about the generation and evolution mechanisms of pavement asphalt aging. In this study, asphalt was aged using self-developed test equipment that took all factors, including heat, ultraviolet radiation and water, into consideration. Then the surface structure and mechanical properties were explored with an optical microscope and atomic force microscopy. The results show that two characteristic regions appear at the surface of samples after aging. The mechanical properties of the two regions were measured using AFM force curve measurements. We found that the adhesion ability of the aged film was much less than that of virgin asphalt, whereas the hardness and modulus of the aged film were significantly greater. However, the adhesion ability, hardness and modulus of the valley area were similar to unaged asphalt binder. Finally, we presented the possible generation and evolution mechanisms on the aging of the asphalt binder.

Hot-pressing for improving performance of CNT/conjugated polymer thermoelectric films and power generators

Abstract: This study demonstrates a post-treatment method for enhancing the thermoelectric power factor of carbon nanotube (CNT)/conjugated polymer nanocomposite films. For the fabrication of the nanocomposite films a mixture of P3HT (50 wt%) and few-walled CNT (50 wt%) in o-dichlorobenzene (oDCB), or a mixture of PEDOT:PSS (50 wt%) and few-walled CNT (50 wt%) in distilled deionized (DDI) water was used. The uniaxial hot-pressing treatment of the as-prepared nanocomposite films resulted in their densification and increased the electrical conductivity and power factor. It was found that the thermoelectric power factor of the CNT/P3HT and CNT/PEDOT:PSS nanocomposite films increased from 150 ± 9 to 217 ± 30 μW m−1K−2, and from 371 ± 44 to 572 ± 92 μW m−1K−2, respectively, after hot-pressing. We fabricated organic thermoelectric generators using the hot-pressed CNT/conjugated polymer nanocomposites and evaluated their capabilities of electrical power generation. The maximum power outputs of the hot-pressed CNT/P3HT and CNT/PEDOT:PSS OTEGs were 46.0 and 36.3 nW, respectively, under a temperature difference of 10 K.

Functionalised solids delivering bioactive nitric oxide gas for therapeutic applications

Abstract: It is well established that nitric oxide is an effective vasodilative, antibacterial and tumoricidal agent, however its targeted delivery in a controllable manner is challenging but necessary for successful therapeutic applications. In recent years a few new methods have been developed, based on the formation of N-diazeniumdiolates, S-nitrosothiols and metal [sbnd]NO coordination bonds in material structures. The typical delivery materials include nanoporous materials (such as zeolites and metal organic frameworks), silicate particles and polymers containing amine and thiol functional groups. These materials are of promising potential for delivering controllable doses of bioactive NO gas to meet the unmet therapeutic needs in the future. This review summarises these delivery materials and relevant biological assessments. Further improvement of current methods and new design of NO donors are still required in order to address the issues on NO storage and its release profile in matching with the clinical requirements.

Antibacterial and antioxidant photoinitiated epoxy co-networks of resorcinol and eugenol derivatives

Abstract: In this study, we used photo-induced cationic reactions to design bio-based crosslinked co-networks from resorcinol diglycidyl ether ( R ) and an eugenol derivative (epoxy eugenol EE ) synthesized by nucleophilic substitution The aim of this work is to prepare new UV-cured co-networks thanks to the cationic polymerization of the epoxides with a covalent immobilization of the eugenol derivative ( EE ) as antioxidant and antibacterial agent to investigate the impact of the proportion of this one on biological activities Moreover, the antibacterial and antioxidant properties of the networks were studied in vitro against two pathogenic bacteria strains: Escherichia coli and Staphylococcus aureus and the DPPH method respectively The results had shownon the one hand a promising anti-adherence forthe both strains without any diffusion of the eugenol derivative which will allow potential applications of these networks for anti-bacterial adhesion and, on the other hand an anti-oxidant activity

Effect of thermal annealing on structural, optical and electrical properties of transparent Nb2O5 thin films

Abstract: We report on the structural, optical and electrical properties of RF sputtered Niobium pentoxide (Nb2O5) thin films. The structural studies have been carried out using XRD, and AFM techniques. Optical constants such as optical band gap energy, absorption coefficient, refractive index, complex dielectric constant and optical conductivity have been estimated for as-deposited and annealed Nb2O5 thin films. The estimated direct optical band gap energy values were found to be E g d = 3.62 e V for the as deposited which decreases to E g d = 3.07 e V for the annealed films at 973 K. The dispersion curves of the refractive index of Nb2O5 thin films in the optical transparency region are explained by using single oscillator and Drude models. The correlations between optical parameters and the annealing temperature of the Nb2O5 thin films are discussed. The DC activation energy has been estimated by using two probe technique.Mott’s variable range hopping conduction process (VRH) and small-polaron hopping have been used to understand DC electrical conductivity.

Layer by Layer-functionalized rice husk particles: A novel and sustainable solution for particleboard production

Abstract: Rice husk particles from agro-wastes have been treated with a Layer by Layer (LbL) deposition of polyelectrolytes and further assembled to prepare a bio-based particle board. The all polymer system employed uses a branched polyethyleneimine combined with a polyacrylic acid. The two polyelectrolytes show a super-linear growth as demonstrated by infrared spectroscopy. A schematic description of the mechanism behind the LbL deposition on rice husk particles is proposed and discussed on the basis of electron microscopy observations. The mechanical properties of the prepared LbL-joined particle boards are evaluated and related to the unique structure and intermolecular ionic interaction occurring between the assembled polyelectrolytes. Only 2 BLs allow for the preparation of a free-standing/self-supporting material. Boards assembled with 3 and 4 BL-coated particles yielded impressive storage moduli of 1.7 and 2.2 GPa, respectively, as measured by dynamic mechanical analyses performed at different temperatures and relative humidities. When tested by three points bending mechanical tests the same materials showed an elastic moduli up to 3.2 GPa and a tensile strengths up to 12 MPa. The presented results demonstrate that the LbL functionalization of agro-waste particles represents an attractive, functional and sustainable solution for the production of mechanically strong particleboards.

TiO2 nanoparticles-functionalized two-dimensional WO3 for high-performance supercapacitors developed by facile two-step ALD process

Abstract: TiO 2 nanoparticles-functionalized two-dimensional (2D) WO 3 (TiO 2 NP-WO 3 ) films fabricated by the facile two-step atomic layer deposition (ALD) process with following post-annealing at 380 °C were investigated as electrode material for supercapacitors. The surface functionalization of 2D WO 3 electrode by TiO 2 nanoparticles significantly enhanced the specific capacitance by ∼1.5 times over the pure 2D WO 3 electrode. Transition of electric double-layer capacitive behavior to the pseudo-capacitive behavior was also observed. Besides, the TiO 2 NP-WO 3 electrode exhibited faster charge transfer than the pure 2D WO 3 electrodes, due to the conduction modulation from the development of TiO 2 -WO 3 heterojunctions. The decoration of TiO 2 nanoparticles on 2D WO 3 electrodes by this two-step ALD process with the following post-annealing has been solidly proven to a facile and effective method to enhance supercapacitor performances along with advantage of ALD technique for fabrication of large-scale, ultrathin films over other conventional methods. The fabrication strategy of the 2D TiO 2 NP-WO 3 electrodes presented in this work may open a new pathway for the design and functionalization of the other 2D nanomaterials for the energy conversion and storage devices.

Effects of Mg doping on electrical properties of Ba0.7Ca0.3TiO3 ceramics

Abstract: (Ba07Ca03)Ti1-xMgxO3-x ceramics where x = 0, 0005, 0015 and 002 were prepared employing a solid state sintering technique The abrupt decrease of tetragonality was induced by doping with x ≥ 0015 Ti K-edge X-ray Absorption Near-Edge Structure (XANES) spectra indicated spontaneous polarization weakness of doped ceramics The grain size was decreased due to the creation of oxygen vacancies and solute-drag effect The reduction of the phase transition temperature, ferroelectricity and piezoelectricity was observed in correlation with the decrease in tetragonality Dielectric properties near room temperature of the samples could be enhanced with Mg addition The results here suggested that the electrical properties of this ceramic may be largely tunable by Mg dopant and could be an attractive material for high-dielectric response devices

Effect of carboxylated graphene nanoplatelets on mechanical and in-vitro biological properties of polyvinyl alcohol nanocomposite scaffolds for bone tissue engineering

Abstract: Owing to the drastically increasing occurrence of bone disorders, it is essential to develop synthetic materials suitable for bone tissue regeneration. In the present study, biocomposite scaffolds of polyvinyl alcohol (PVA) reinforced with different concentrations of functionalized graphene nanoplatelets (GNP: 0, 0.5, 1 and 1.5 wt%) were prepared using freeze drying method. The prepared scaffolds were characterized for their physicochemical, mechanical and in-vitro biological properties. To study the effect of GNP reinforcement on the MG-63 osteoblast cells behavior scanning electron microscopy (SEM), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, alkaline phosphatase (ALP) activity assay and alizarin red stain-based (ARS) assay were performed. The homogenous dispersion of GNP up to 1 wt% improved the mechanical and biological properties of the nanocomposite scaffolds. The tensile strength of the scaffolds with 1 wt% of GNP was found to be 16.48 ± 0.50 MPa which is 20.68 times more than the PVA sample. The low concentration of GNP (1 wt%) provided the most favorable microenvironment for osteoblast cell proliferation and differentiation. Further increase in GNP concentration (1.5 wt%) lead to agglomeration of GNP which deteriorates the properties of nanocomposite. The study showed that the relatively low concentration of GNP in PVA-GNP scaffolds certainly exhibit a beneficial effect on the mechanical and biological properties of nanocomposite scaffolds, thus proving to be a promising biomaterials for bone tissue engineering applications.

Unified ring-compression model for determining tensile properties of tubular materials

Abstract: The stress-strain relation is the key mechanical properties in safety design and evaluation for tubular structures. However, conventional uniaxial tension and compression tests have some drawbacks and limitations for these structures. In the current investigation, a unified ring-compression model to acquire the stress–strain relation of tubular material is introduced based on the equivalent energy principle. In the model, a unified relation among strain energy, load, deflection, geometric parameters and material property parameters is proposed to depict the elastoplastic response during ring compression test. The model has only four undetermined parameters which can be calibrated by a few FEA (finite element analysis) calculations. The accuracy of the model has been verified within a wide range of imaginary materials by using FEA. Results show that both the forward-predicted load-deflection relation and the reverse-predicted stress-strain relations from the model are in excellent accord with the results from FEA. In addition, the model is verified with three homogeneous ductile materials by conducting ring compression and standard tensile tests. And it is applied in obtaining the hoop stress-strain relation of tubular zirconium alloy in the nuclear power engineering.

Deoxy-sugar releasing biodegradable hydrogels promote angiogenesis and stimulate wound healing

Abstract: Vascular endothelial growth factor (VEGF) stimulates endothelial cells to migrate, proliferate and form new blood vessels. However direct delivery of VEGF has not become clinically adopted as a means of stimulating blood vessel formation and wound healing because of its relatively poor stability and its production of immature blood vessels. A simpler way of stimulating production of VEGF in situ is explored in this study following reports of deoxy sugars involved in inducing VEGF production. The pro-angiogenic effect of L and D isomers of deoxy sugars (ribose, fucose and rhamnose) loaded into biodegradable chitosan/collagen hydrogels was examined using a chick chorionic allantoic membrane assay. The L-sugars were all pro-angiogenic but only the 2-deoxy-D-ribose had strong effects on angiogenesis. Furthermore, these sugars could not be metabolised by four strains of Staphylococcus aureus, as a metabolic substrate for growth, although some of these could be metabolised by another typical pathogen, Pseudomonas aeruginosa. The effects of 2-deoxy-D-ribose in a chitosan/collagen hydrogel on wound healing were also assessed. This biomaterial doubled the rate of cutaneous wound healing in rats associated with an increase in vascularisation detected by staining for CD34 positive cells.

Fabrication of carbon nanotube/copper and carbon nanofiber/copper composites for microelectronics

Abstract: Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) exhibit high ampacity, the key property needed for next-generation interconnects at miniaturized scales. Copper (Cu), the current state-of-the-art material used in interconnects, faces reliability issues at further miniaturized scales. This is due to high current density causing electromigration of Cu atoms. Therefore, CNTs and CNF were proposed to replace Cu in next-generation microelectronics. Using standalone CNT or CNF structures is very challenging and achieving the same properties as an individual CNT or CNF is difficult. The difficulty arises because the electrical properties of a grown forest depend on characteristics of the forest including self-alignment, density and mechanical stability. Thus, in this study, Cu is used to densify self-aligned CNTs and CNFs so that the mechanical stability and high density can be achieved. Parameters that impact the quality of the final Cu–CNT composite layer including the CNT qualities and fabrication techniques, CNT underlayer effect and different Cu deposition techniques are investigated. Different Cu deposition techniques on the as-grown CNTs are also experimented including electroplating, electroless plating and physical vapor deposition (PVD). The experiments show that although CNFs were successfully coated with Cu using electroless plating, CNTs are found to be fragile and are dissolved during the process of electroless plating. Furthermore, it was found that CNTs cannot act as seed layer for Cu. Other underlayer material such as Ti and TiN were found difficult to work with due to several reasons. Ti and TiN were not found a good material to grow vertically aligned CNTs using CVD. However, PECVD combined with TiN underlayer was successful in obtaining vertically aligned CNTs, although with a much slower growth rate compared to CNTs grown on Al2O3 underlayer. However, TiN was not successful in terms of electroplating.