Showing papers in "Journal of Materials Science in 2014"

A review: carbon nanofibers from electrospun polyacrylonitrile and their applications

Abstract: Carbon nanofibers with diameters that fall into submicron and nanometer range have attracted growing attention in recent years due to their superior chemical, electrical, and mechanical properties in combination with their unique 1D nanostructures. Unlike catalytic synthesis, electrospinning polyacrylonitrile (PAN) followed by stabilization and carbonization has become a straightforward and convenient route to make continuous carbon nanofibers. This paper is a comprehensive and state-of-the-art review of the latest advances made in development and application of electrospun PAN-based carbon nanofibers. Our goal is to demonstrate an objective and overall picture of current research work on both functional carbon nanofibers and high-strength carbon nanofibers from the viewpoint of a materials scientist. Strategies to make a variety of carbon nanofibrous materials for energy conversion and storage, catalysis, sensor, adsorption/separation, and biomedical applications as well as attempts to achieve high-strength carbon nanofibers are addressed.

Extracting hydroxyapatite and its precursors from natural resources

Abstract: Healing of segmental bone defects remain a difficult problem in orthopedic and trauma surgery. One reason for this difficulty is the limited availability of bone material to fill the defect and promote bone growth. Hydroxyapatite (HA) is a synthetic biomaterial, which is chemically similar to the mineral component of bones and hard tissues in mammals and, therefore, it can be used as a filler to replace damaged bone or as a coating on implants to promote bone in-growth into prosthetic implants when used in orthopedic, dental, and maxillofacial applications. HA is a stoichiometric material with a chemical composition of Ca10(PO4)6(OH)2, while a mineral component of bone is a non-stoichiometric HA with trace amounts of ions such as Na+, Zn2+, Mg2+, K+, Si2+, Ba2+, F−, CO32−, etc. This review looks at the progress being made to extract HA and its precursors containing trace amount of beneficial ions from biological resources like animal bones, eggshells, wood, algae, etc. Properties, such as particle size, morphology, stoichiometry, thermal stability, and the presence of trace ions are studied with respect to the starting material and recovery method used. This review also highlights the importance of extracting HA from natural resources and gives future directions to the researcher so that HA extracted from biological resources can be used clinically as a valuable biomaterial.

The structure, microphase-separated morphology, and property of polyurethanes and polyureas

Abstract: The structure–morphology–property relationship of thermoplastic polyurethanes and polyureas was reviewed. The effect of hard segment structure and chemistry, and the hydrogen bonding on the morphology and properties of polyurethanes elastomers was presented. Special attention was made on polyureas with strong bidentate hydrogen bonding, and they are important candidates for thermoplastic elastomers with processibility by careful selection of the hard segment symmetry and hydrogen bonding capacity.

Review of thermal stability of nanomaterials

Abstract: Current developments in kinetic and thermodynamic stabilization of grains in nanostructured metals, alloys, and compounds are generalized and discussed in detail. As applied to the thermodynamic approach, attention has recently shifted from using the regular solution approximation to estimating thermodynamic properties of nanomaterials by considering both inner regions of nanograins and their grain boundaries. This situation is discussed and examples for alloys based on iron, copper, tungsten, and other elements are presented. Experimental information about behavior of nanomaterials subjected to radiation or oxidation is considered, along with recent experiments on abnormal grain growth.

Different models of hardness evolution in ultrafine-grained materials processed by high-pressure torsion

Abstract: High-pressure torsion (HPT) is an attractive processing method in severe plastic deformation techniques involving the application of high compressive pressure with concurrent torsional straining. Excellent grain refinement is anticipated when using this technique to average grain sizes of the submicrometer or even nanometer ranges. Because of the significant microstructural changes during processing, there are numerous reports showing evolution in local hardness toward homogeneity throughout a disk diameter with increasing numbers of revolutions. The achieved hardness after HPT is mostly much higher than that in the as-received condition because of exceptional grain refinement although there are a limited number of metals and alloys showing softening or weakening after HPT processing. This paper was initiated to review recent discoveries in the experimental results on hardness evolution toward homogeneity during HPT processing and discuss the different models of hardness developments with respect to imposed equivalent strain by HPT processing for a range of metals and alloys. Moreover, recent results of hardness homogeneity and heterogeneity through thicknesses of the processed disks are discussed toward a complete understanding of hardness evolution in the UFG metals processed by HPT.

Three-dimensional magnetic graphene oxide foam/Fe3O4 nanocomposite as an efficient absorbent for Cr(VI) removal

Abstract: We developed a novel three-dimensional (3D) graphene oxide foam/Fe3O4 nanocomposite (GOF/Fe3O4) and evaluated its adsorption performance for Cr(IV) removal. The 3D free-standing graphene foam was firstly synthesized on nickel foam and then oxidized and magnetically functionalized with Fe3O4 nanoparticles to form GOF/Fe3O4. The GOF/Fe3O4 exhibited a very large surface area of 574.2 m2/g, a high saturation magnetization of 40.2 emu/g, and a maximum absorption capacity of 258.6 mg/g for Cr(IV) removal, which significantly outperformed the reported 2D graphene-based adsorbents and other conventional adsorbents. The present work may offer a way to prepare a range of 3D magnetic graphene-based adsorbents for application in effective removal of heavy metal ions.

Enhanced thermal conductivity in polymer composites with aligned graphene nanosheets

Abstract: We developed highly aligned graphene nanosheets (GNSs) in epoxy composites with incorporating magnetic GNS–Fe3O4 hybrids under a magnetic field with the aim to take full advantage of the high inplane thermal conductivity of graphene. GNS–Fe3O4 hybrids were fabricated by a simple coprecipitation method, and their morphology, chemistry, and structure were characterized. GNS–Fe3O4 hybrids were found to be homogenously dispersed and well aligned through the direction of the magnetic field in the epoxy matrix, as confirmed by SEM observation and Raman spectra analysis. The resulting epoxy/GNS–Fe3O4 composites possessed high thermal conductivity in a parallel magnetic-alignment direction at low GNS–Fe3O4 loadings, which greatly outperformed the composites with randomly dispersed bare GNSs. The obtained results indicated that the magnetic alignment of magnetic-functionalized GNSs is an effective way for greatly improving the thermal conductivity of the graphene-based composites.

Intumescent flame retardant polyurethane/reduced graphene oxide composites with improved mechanical, thermal, and barrier properties

Abstract: Intumescent flame retardant polyurethane (IFRPU) composites were prepared in the presence of reduced graphene oxide (rGO) as synergism, melamine, and microencapsulated ammonium polyphosphate. The composites were examined in terms of thermal stability (both under nitrogen and air), electrical conductivity, gas barrier, flammability, mechanical, and rheological properties. Wide-angle X-ray scattering and scanning electron microscopy indicated that rGO are well-dispersed and exfoliated in the IFRPU composites. The limiting oxygen index values increased from 22.0 to 34.0 with the addition of 18 wt% IFR along with 2 wt% rGO. Moreover, the incorporation of rGO into IFRPU composites exhibited excellent antidripping properties as well as UL-94 V0 rating. The thermal stability of the composites enhanced. This was attributed to high surface area and good dispersion of rGO sheets induced by strong interactions between PU and rGO. The oxygen permeability, electrical, and viscoelasticity measurements, respectively, demonstrated that rGO lead to much more reduction in the gas permeability (by ~90 %), high electrical conductivity, and higher storage modulus of IFRPU composites. The tensile strength, modulus, and shore A remarkably improved by the incorporation of 2.0 wt% of rGO as well.

Impact of different coating processes of microfibrillated cellulose on the mechanical and barrier properties of paper

Abstract: This study presents a comparison of the mechanical and barrier properties of papers coated with microfibrillated cellulose (MFC) by two different coating processes: (i) bar coating and (ii) size press. Due to the high water content of MFC, water-treated papers were taken as references to highlight the effects of MFC on the properties of papers. Structural, mechanical and barrier properties of the ensued materials were performed respectively with SEM, tensile and stiffness testers, and air and oxygen permeability equipments. The properties of the water-treated papers were considerably damaged compared to those of the base paper that underlined the negative impact of both coating processes on the papers structure. With MFC, the air barrier and the bending stiffness were considerably improved (+90 and +50 % respectively), especially when the bar coating was used, i.e. with 7 g m−2 of MFC. Size press was indeed not able to considerably improve papers properties as the MFC coat weight barely reached 4 g m−2 resulting from ten successive MFC layers.

Harmonic-structured copper: performance and proof of fabrication concept based on severe plastic deformation of powders

Abstract: Pure copper (Cu) having bimodal ‘harmonic structure’ (HS) was fabricated by a technique based on severe plastic deformation of powders, which involved tailored mechanical milling and spark plasma sintering. The harmonic-structured Cu demonstrates a unique combination of high strength and large elongation superior to its homogeneous as well as bimodal heterogeneous counterparts. Specific features of harmonic structure, i.e. continuous network of ultra-fine grained (UFG) regions encompassing coarse-grained areas, lead to the extension of uniform elongation. The optimum combination of properties in pure Cu is found to be in the harmonic-structured material having 40 % UFG fraction.

Highly enhanced mechanical properties in Cu matrix composites reinforced with graphene decorated metallic nanoparticles

Abstract: This study investigated the preparation and mechanical performance of graphene/metal composites using Ni nanoparticles decorated graphene nanoplatelets (Ni-GPLs) as a reinforcing component in Cu matrix (Ni-GPL/Cu). Ni-GPLs consisting of well-dispersed Ni nanoparticles strongly attached on GPLs were successfully synthesized by chemically reducing Ni ions on the surface of GPLs. The Ni-GPL/Cu composites with only 0.8 vol% Ni-GPLs exhibited a significant improvement in ultimate tensile strength (UTS), being 42 % higher than that of monolithic Cu. The significant strength enhancement is attributed to the unique structure of Ni-GPLs, which was expected to generate a good dispersion and strong GPL–Cu interfacial bonding. The UTS of 0.8 vol% GPL/Cu composites was even lower than that of the monolithic Cu due to the GPL aggregates. The obtained results indicated that Ni-GPLs are novel and effective reinforcing components for greatly improving the mechanical properties of the graphene/metal composites.

Preparation, characterization, viscosity, and thermal conductivity of nitrogen-doped graphene aqueous nanofluids

Abstract: Nanofluids perform a crucial role in the development of newer technologies ideal for industrial purposes. In this study, Nitrogen-doped graphene (NDG) nanofluids, with varying concentrations of nanoparticles (0.01, 0.02, 0.04, and 0.06 wt%) were prepared using the two-step method in a 0.025 wt% Triton X-100 (as a surfactant) aqueous solution as a base. Stability, zeta potential, thermal conductivity, viscosity, specific heat, and electrical conductivity of nanofluids containing NDG particles were studied. The stability of the nanofluids was investigated by UV–vis over a time span of 6 months and concentrations remain relatively constant while the maximum relative concentration reduction was 20 %. The thermal conductivity of nanofluids was increased with the particle concentration and temperature, while the maximum enhancement was about 36.78 % for a nanoparticle loading of 0.06 wt%. These experimental results compared with some theoretical models including Maxwell and Nan’s models and observed a good agreement between Nan’s model and the experimental results. Study of the rheological properties of NDG nanofluids reveals that it followed the Newtonian behaviors, where viscosity decreased linearly with the rise of temperature. It has been observed that the specific heat of NDG nanofluid reduced gradually with the increase of concentration of nanoparticles and temperature. The electrical conductivity of the NDG nanofluids enhanced significantly due to the dispersion of NDG in the base fluid. This novel type of fluids demonstrates an outstanding potential for use as innovative heat transfer fluids in medium-temperature systems such as solar collectors.

Bamboo fibers for composite applications: a mechanical and morphological investigation

Abstract: Bamboo fibers are very promising reinforcements for polymer composites production due to its high aspect ratio and strong mechanical performances. In order to better understand their reinforcing potential, the mechanical properties of single bamboo fibers extracted from eleven commercial bamboo species in China were measured with a newly developed microtensile technique. For comparison, the mechanical properties of mature single Chinese Fir and Masson Pine wood fibers were measured. The results show that the average longitudinal tensile modulus of the eleven kinds of bamboo fibers ranges from 25.5 to 46.3 GPa with an average value of 36.7 GPa. For tensile strength, the value ranges from 1.20 to 1.93 GPa with an average value of 1.55 GPa. The tensile strength and modulus of bamboo fibers are nearly two times of that of single Chinese Fir and Masson Pine fibers, and significantly higher than most of the published data for other softwood fibers. The average elongation at break of bamboo fibers is about 4.84 %, only a little lower than the value 5.15 % of the tested mature softwood fibers. Additionally, bamboo fibers were found to have smaller diameters and larger aspect ratio than most documented wood fibers, which favored an improved reinforcing effect. These combined mechanical and morphological advantages highlight the potential of bamboo fibers as the reinforcing phase in polymer composites for structural purpose.

Thermal and electrical conductivity of binary magnesium alloys

Abstract: Thermal conductivity is a key parameter for thermal design and management of the electronic components in their passive cooling processes. In this work, thermal and electrical conductivities of six groups of binary Mg alloys (Mg–Al, Mg–Zn, Mg–Sn, Mg–Zr, Mg–Mn, and Mg–Ca) in as-cast, as-solution, and annealed states were measured and the corresponding microstructures were observed. In both as-cast and as-solution states, thermal/electrical conductivities of the six groups of Mg alloys decreased with composition. Effects of solution treatment and annealing on thermal/electrical conductivities of the as-cast samples were also investigated and discussed. Moreover, the specific thermal/electrical resistivity (thermal/electrical resistivity increment of the alloy derived from one atom addition) of the solute elements for Mg alloys was drawn as follows, Zn < Al < Ca < Sn < Mn < Zr. Atomic volume difference of the solute elements with Mg atom (ΔV/V Mg), valency, and configuration of extra-nuclear electron of the solute were believed as the main reasons for the differences.

Fabrication of cyclodextrin nanosponges for quercetin delivery: physicochemical characterization, photostability, and antioxidant effects

Abstract: Quercetin is a flavonoid widely distributed in vegetables and fruits and exhibits strong antioxidant activity, but the poor solubility and stability of quercetin limit its function and application The purpose of this study was to enhance the dissolution rate and stability of a poorly water-soluble drug quercetin by complexation with cyclodextrin-based nanosponges Nanosponges are recently developed sponge-like structures and have the capacity to interact with small molecules in its matrix In this study, five types of nanosponges were purposely designed by varying the molar ratio of β-cyclodextrin and diphenyl carbonate Quercetin was loaded into nanosponges by freeze-drying method The particle sizes of plain and quercetin-loaded nanosponges are in between 40 and 100 nm with low polydispersity indices Zeta potential is sufficiently high to obtain a stable colloidal nanosuspension Fourier transformed infrared, Raman spectroscopy, differential scanning calorimetry, and X-ray powder diffraction studies confirmed the interaction of quercetin with nanosponges Particle sizes measured from TEM images were in agreement with DLS results The dissolution of the quercetin nanosponges was significantly higher compared with the pure drug The stability of encapsulated quercetin nanosponge was tracked in a simulated intestinal fluid A marked improvement in the photostability was also observed In addition, the antioxidant activity of the quercetin nanosponges was more effective than pure quercetin on DPPH scavenging, anti-superoxide formation, and superoxide anion scavenging These results signify that nanosponge formulations can be used as effective nanocarriers for the delivery of quercetin

The water vapour sorption behaviour of acetylated birch wood: how acetylation affects the sorption isotherm and accessible hydroxyl content

Abstract: The water vapour sorption isotherms and sorption kinetics of birch (Betula pendula L) acetylated to different levels have been determined using a dynamic vapour sorption (DVS) apparatus. A DVS instrument was also used to determine the accessible hydroxyl content in the wood samples using deuterium exchange. The results are reported in terms of the reduced equilibrium moisture content (EMCR), in which the moisture content per unit mass of wood substance is used for the calculation. As the level of acetylation of the wood samples increased there was a corresponding reduction in EMCR of the wood samples, which was accompanied by a decrease in hysteresis in the same order. The sorption kinetics were also determined using the DVS and analysed using the parallel exponential kinetics model, in which the sorption kinetics curve is composed of two processes (labelled fast and slow). Using this analysis, it is possible to calculate two pseudo-isotherms associated with the two processes. The sorption isotherm is a composite of the sorption isotherms associated with the fast process water and the slow process water and there are significant differences in behaviour between the two. It is suggested in this paper that the fast process is related to diffusion limited kinetics, whereas the slow process is a relaxation-limited phenomenon. The reduction in accessible OH content due to acetylation was well correlated with the weight gain due to acetylation, although the relationship did not exactly correspond with that theoretically determined.

Metal ion biosorption on chitosan for the synthesis of advanced materials

Abstract: Chitosan is an aminopolysaccharide that binds metal ions through different mechanisms such as ion exchange, chelation or formation of ternary complex. The sorption performance depends on the characteristics of the solution (pH, presence of ligands, metal speciation) and the properties of the biopolymer (crystallinity, degree of deacetylation, molecular weight). Sorption performance is also controlled by the accessibility and availability of reactive groups (diffusion properties). These interactions chitosan/metal ions can be used for environmental applications (recovery of toxic or valuable metals) but also for the synthesis of new materials. Hybrid materials (chitosan/metal ion composites) can thus be used for manufacturing new sorbents with improved functionalities, supported catalysts, antimicrobial supports and sensors. The physical versatility of the biopolymer is an important criterion for designing these new materials: The conditioning of the material under the form of hydrogel beads, membranes, fibers and hollow fibers, foams and sponges enhances sorption performance and allows developing new applications.

Utilization of sweet sorghum fiber to reinforce fly ash-based geopolymer

Abstract: Geopolymer has been of great research interest as a material for sustainable development. As ordinary Portland cement, however, geopolymer exhibits brittle behavior with low tensile strength, ductility, and fracture toughness. This paper investigates the reinforcement of fly ash-based geopolymer with alkali-pretreated sweet sorghum fiber. The sweet sorghum fiber comes from the bagasse (residue), a waste after the juice is extracted from sweet sorghum stalks for ethanol production. Specifically, the unit weight of fly ash-based geopolymer specimens containing different contents of sweet sorghum fibers was measured. Unconfined compression, splitting tensile, and flexural tests were conducted to investigate the effect of incorporated sweet sorghum fiber on the mechanical properties of fly ash-based geopolymer. Scanning electron microscopy imaging was also performed to study the microstructure of the sweet sorghum fiber–geopolymer composite. The results indicate that the unit weight of the sweet sorghum fiber–geopolymer composite decreases with higher fiber content. Although the inclusion of sweet sorghum fiber slightly decreases the unconfined compressive strength, the splitting tensile, and flexural strengths as well as the post-peak toughness increase with the fiber content up to 2 % and then start to decrease. The splitting tensile tests also clearly show the transition from the brittle failure of the plain geopolymer specimen to the “ductile” failure of the geopolymer specimen containing sweet sorghum fiber.

SnO2/g-C3N4 photocatalyst with enhanced visible-light photocatalytic activity

Abstract: Visible light-responsive SnO2/g-C3N4 nanocomposite photocatalysts were prepared by ultrasonic-assisting deposition method with melamine as a g-C3N4 precursor. The as-prepared photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy, Fourier transform infrared spectra and photoluminescence emission spectra. The photocatalytic activities of the samples were evaluated by monitoring the degradation of methyl orange solution under visible light irradiation (wavelength ≥400 nm). The results show that the SnO2 nanoparticles with the size of 2–3 nm are dispersed on the surface of g-C3N4 evenly in SnO2/g-C3N4 nanocomposites. The visible-light photocatalytic activity of SnO2/g-C3N4 nanocomposites is much higher than that of pure g-C3N4, and increases at first and then decreases with the increment of the content of g-C3N4 in the nanocomposites. The visible-light photocatalytic mechanism of the investigated nanocomposites has been discussed.

Synthesis of well-dispersed Ag nanoparticles on eggshell membrane for catalytic reduction of 4-nitrophenol

Abstract: A novel functional bio-nanocomposite was prepared by deposition of Ag nanoparticles onto the surface of natural eggshell membrane fibers. Practically, the functional groups exposed on the fiber surface can provide locations to anchor Ag ions when immersed into metal precursor solution. The synthesized small-sized Ag nanoparticles with uniform distribution is well decorated on the surface of interwoven fibers of eggshell membrane. The effectiveness of the as-prepared AgNPs/ESM composites as a solid phase heterogeneous catalyst has been evaluated, for the first time, on the well-known 4-nitrophenol reduction to 4-aminophenol in the presence of excess borohydride. Moreover, the kinetics of the reduction reaction was investigated at different temperatures to determine the activation energy. This work provides an important example in the introduction of natural membranes for the fabrication of functional hybrid nanocomposites which could be very useful in varying fields.

Review: effect of bimetal interface structure on the mechanical behavior of Cu–Nb fcc–bcc nanolayered composites

Abstract: This article reviews the growing body of work over the past decade investigating the effect of interface crystallographic character and resulting local interface structure on the mechanical behavior in bimetallic nanolayered composites. It has been shown that nanolayered composites exhibit enhanced strength, thermal stability, radiation damage tolerance, and resistance to shock deformation in comparison to their coarse-grained constituents. These unique behaviors are attributable to the high density of interfacial content, as well as the local interface structure and its influence on mechanically or irradiation-induced defects. Here, we cover recent literature on Cu–Nb nanolayered composites synthesized via different pathways including physical vapor deposition and severe plastic deformation techniques such as accumulative roll bonding. By altering the synthesis method, we can produce materials with similar chemical composition and layered morphology, while varying only the crystallographic character of the interface as defined by the orientation relationship and interface plane. This capability, in turn, opens an unprecedented opportunity for systematic investigation of the local interface structure on subsequent behavior, while keeping all other variables constant. We begin with a discussion of interface structures that develop as a function of their processing path. We then follow with the effects of interface structure on dislocation nucleation and deformation twinning. Next, we discuss interface effects on mechanical behavior at quasi-static ambient conditions and later under extreme strains, strain rates, and temperatures. Taken together, these examples provide a strong indication that interface structure matters. The exciting implication is that bimetal interfaces can potentially be engineered for optimal material performance.

Mechanical characterization of hollow ceramic nanolattices

Abstract: In the analysis of complex, hierarchical structural meta-materials, it is critical to understand the mechanical behavior at each level of hierarchy in order to understand the bulk material response. We report the fabrication and mechanical deformation of hierarchical hollow tube lattice structures with features ranging from 10 nm to 100 μm, hereby referred to as nanolattices. Titanium nitride (TiN) nanolattices were fabricated using a combination of two-photon lithography, direct laser writing, and atomic layer deposition. The structure was composed of a series of tessellated regular octahedra attached at their vertices. In situ uniaxial compression experiments performed in combination with finite element analysis on individual unit cells revealed that the TiN was able to withstand tensile stresses of 1.75 GPa under monotonic loading and of up to 1.7 GPa under cyclic loading without failure. During the compression of the unit cell, the beams bifurcated via lateral-torsional buckling, which gave rise to a hyperelastic behavior in the load–displacement data. During the compression of the full nanolattice, the structure collapsed catastrophically at a high strength and modulus that agreed well with classical cellular solid scaling laws given the low relative density of 1.36 %. We discuss the compressive behavior and mechanical analysis of the unit cell of these hollow TiN nanolattices in the context of finite element analysis in combination with classical buckling laws, and the behavior of the full structure in the context of classical scaling laws of cellular solids coupled with enhanced nanoscale material properties.

Secondary crystalline phases identification in Cu $$_2$$ 2 ZnSnSe $$_4$$ 4 thin films: contributions from Raman scattering and photoluminescence

Abstract: In this work, we present the Raman peak positions of the quaternary pure selenide compound Cu\(_2\)ZnSnSe\(_4\) (CZTSe) and related secondary phases that were grown and studied under the same conditions. A vast discussion about the position of the X-ray diffraction (XRD) reflections of these compounds is presented. It is known that by using XRD only, CZTSe can be identified but nothing can be said about the presence of some secondary phases. Thin films of CZTSe, Cu\(_2\)SnSe\(_3\), ZnSe, SnSe, SnSe\(_2\), MoSe\(_2\) and a-Se were grown, which allowed their investigation by Raman spectroscopy (RS). Here we present all the Raman spectra of these phases and discuss the similarities with the spectra of CZTSe. The effective analysis depth for the common back-scattering geometry commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated for different wavelength values. The observed asymmetric PL band on a CZTSe film is compatible with the presence of CZTSe single-phase and is discussed in the scope of the fluctuating potentials' model. The estimated bandgap energy is close to the values obtained from absorption measurements. In general, the phase identification of CZTSe benefits from the contributions of RS and PL along with the XRD discussion.

Fabrication and characterization of PCL/gelatin/chitosan ternary nanofibrous composite scaffold for tissue engineering applications

Abstract: In the present study, we have fabricated a ternary composite nanofibrous scaffold from PCL/gelatin/chitosan, by electrospinning technique, using a solvent system—chloroform/methanol for polycaprolactone (PCL) and acetic acid for gelatin and chitosan, for tissue engineering applications. Field emission scanning electron microscopy (FE-SEM) was used to investigate the fiber morphology of the scaffold and it was found that the fiber morphology was influenced by the concentrations of PCL, gelatin, and chitosan in polymer solution during electrospinning. X-ray diffraction, Fourier transform infrared, and thermogravimetric (TG) analysis results showed some interactions among the molecules of PCL, gelatin, and chitosan within the scaffold. In-vitro cell culture studies were done by seeding L929 mouse fibroblasts on fabricated composite scaffold, which confirmed the cell viability, high cell proliferation rate, and cell adhesion on composite scaffold as indicated by MTT assay, DNA quantification, and FE-SEM analysis of cell-scaffold construct. Thus, the ternary composite scaffold made from the combination of PCL (synthetic polymer), gelatin, and chitosan (natural polymer) may find potential application in tissue engineering.

Energy storage properties of (1 − x)(Bi0.5Na0.5)TiO3–xKNbO3 lead-free ceramics

Abstract: In this study, a simple compound (1 − x)(Bi0.5Na0.5)TiO3–xKNbO3 (x = 0 – 0.12) lead-free bulk ceramic was developed for high electric power pulse energy storage applications. The dielectric and ferroelectric properties of the ceramics were measured. The results illustrate that the energy storage density of the ceramics is enhanced by the addition of KNbO3. The influence of applied electric field, temperature, and fatigue on the energy storage properties of the ceramics was evaluated for the composition-optimized (Bi0.5Na0.5)TiO3–0.1KNbO3 ceramic. The results demonstrate that (Bi0.5Na0.5)TiO3–0.1KNbO3 ceramic is a promising lead-free material for high power pulse capacitor applications. The excellent energy storage properties of the (Bi0.5Na0.5)TiO3–0.1KNbO3 ceramics are ascribed to the reversible relaxor–ferroelectric phase transition induced by the electric field.

Microwave-absorbing properties of silver nanoparticle/carbon nanotube hybrid nanocomposites

Abstract: Silver (Ag) nanoparticles fabricated by chemical reduction process were grafted onto the surface of carbon nanotubes (CNTs) to prepare hybrid nanocomposites. The Ag/CNT hybrid nanomaterials were characterized using transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The Ag/CNT hybrid nanomaterials were then loaded in paraffin wax, and pressed into toroidal shape with thickness of 1 mm to evaluate their complex permittivity and complex permeability by scattering parameters measurement method in reflection mode using vector network analyzer. The reflection loss of the samples was calculated according to the transmission line theory using their measured complex permittivity and permeability. The minimum reflection loss of the Ag/CNT hybrid nanocomposite sample with a thickness of 1 mm reached 21.9 dB (over 99 % absorption) at 12.9 GHz, and also exhibited a wide response bandwidth where the frequency bandwidth of the reflection loss of less than −10 dB (over 90 % absorption) was from 11.7 to 14.0 GHz. The Ag/CNT hybrid nanocomposite with thickness of 6 mm showed a minimum reflection loss of ~−32.1 dB (over 99.9 % absorption) at 3.0 GHz and was the best absorber when compared with the other samples of different thickness. The reflection loss shifted to lower frequency as the thickness of the samples increased. The capability to modulate the absorption band of these samples to suit various applications in different frequency bands simply by manipulating their thickness indicates that these hybrid nanocomposites could be a promising microwave absorber.

The rheological behaviour of concentrated dispersions of graphene oxide

Abstract: The rheological behaviour of concentrated aqueous dispersions of graphene oxide (GO) was studied as a model system and then compared to those of GO in poly(methyl methacrylate) (PMMA). Dynamic and steady shear tests were conducted using a parallel plate rheometer. The aqueous system behaved as a reversibly flocculated dispersion with linear viscoelastic regions (LVR) extending up to strains of 10 %. Dynamic frequency sweeps conducted within the LVR showed a classic strong-gel spectrum for high concentrations. Under steady shear, the dispersions shear-thinned up to a Peclet number (Pe) <1, followed by a power law at higher Pe. The dispersions were thixotropic and recovered their structure after 60 min rest. The change in rheological properties of the PMMA upon the addition of the GO was less pronounced possibly due to the absence of hydrogen bonding; a relatively small increase in viscosity was found, which is encouraging for the melt processing of graphene composites.

Size-specified graphene oxide sheets: ultrasonication assisted preparation and characterization

Abstract: The preparation of graphene oxide (GO) sheets with specified size was developed by simply controlling the time of ultrasonication to the large-size GO (LGO) sheets. The LGO sheets were synthesized by choosing large parent graphite, mild oxidation condition and a two-step centrifugation. The different-sized GO samples prepared under different ultrasonication times, are characterized by Scanning electron microscopy, X-ray photoelectron spectroscopy, Ultraviolet–visible spectroscopy, and X-ray diffraction. It is found that the size of the GO sheets, which has a Gaussian distribution, decreases from 231 to 17 μm2 as the ultrasonication time increases. Moreover, the ultrasonication not only can exfoliate and break GO sheets, but also increase the oxidation degree of GO sheets, especially when the GO sheets have a weak oxidation degree. It is reasonable to believe that the size of GO sheets is closely correlated to the C–O content, which enables the size of GO sheets to be controlled. Our work demonstrates that ultrasonication is an important method to control the size and the oxidation degree of GO sheets, to a certain extent.

Nanostructured mesoporous Au/TiO2 for photocatalytic degradation of a textile dye: the effect of size similarity of the deposited Au with that of TiO2 pores

Abstract: Mesoporous Au/TiO2 nanocomposites with different Au particle size (73–118 nm) were synthesized via deposition–precipitation method The synthesized nanocomposites have been characterized by XRD, TEM, XPS, DLS, ICP-OES, N2 sorpometry, and UV–Vis spectroscopy Au/TiO2 showed higher quantum yield and greater photocatalytic efficiency compared to pure TiO2 under both ultraviolet and sunlight illumination The increase of the photocatalytic efficiency of TiO2 upon deposition with gold nanoparticles, Au NPs, is due to the interface electron transfer from Au nanoparticles to TiO2 under visible light illumination and from TiO2 to Au nanoparticles under UV illumination For the first time, the effect of Au particle sizes when it is very similar to the interparticles pores of TiO2 has been investigated The highest reaction rate (57 × 10−2 min−1) and degradation efficiency of Safranin-O (SO) dye (97 %) were observed when the deposited gold nanoparticles are the smallest among the studied samples (sAu/TiO2) In spite of blocking a high percentage of the TiO2 pores, the sAu/TiO2 sample demonstrated a complete degradation of SO dye in 50 min which is more efficient than any other reported catalysts in the literature

Review: the characterization of electrospun nanofibrous liquid filtration membranes

Abstract: Electrospun nanofibrous membranes (ENMs) are used in a variety of applications, including sensors, tissue engineering, air filtration, energy, and reinforcement in composite materials. Recently, they have gained an interest in the field of liquid filtration. The membranes, surface, bulk, and overall architecture play an important role in the filtration properties and hence the right characterization technique needs to be established, which will pave the way for future developments in the field of filtration. In this article, we have reviewed the recent advances in ENMs for liquid separation application.