Al2O3 Nanowires Research Articles

Is nanomaterial- and vancomycin-loaded polymer coating effective at preventing methicillin-resistant Staphylococcus aureus growth on titanium disks? An in vitro study

PurposePeriprosthetic joint infections induced by methicillin-resistant Staphylococcus aureus (MRSA) pose a major socioeconomic burden. Given the fact that MRSA carriers are at high risk for developing periprosthetic infections regardless of the administration of eradication treatment pre-operatively, the need for developing new prevention modalities is high.MethodsThe antibacterial and antibiofilm properties of vancomycin, Al2O3 nanowires, and TiO2 nanoparticles were evaluated in vitro using MIC and MBIC assays. MRSA biofilms were grown on titanium disks simulating orthopedic implants, and the infection prevention potential of vancomycin-, Al2O3 nanowire-, and TiO2 nanoparticle-supplemented Resomer® coating was evaluated against biofilm controls using the XTT reduction proliferation assay.ResultsAmong the tested modalities, high- and low-dose vancomycin-loaded Resomer® coating yielded the most satisfactory metalwork protection against MRSA (median absorbance was 0.1705; [IQR = 0.1745] vs control absorbance 0.42 [IQR = 0.07]; p = 0.016; biofilm reduction was 100%; and 0.209 [IQR = 0.1295] vs control 0.42 [IQR = 0.07]; p < 0.001; biofilm reduction was 84%, respectively). On the other hand, polymer coating alone did not provide clinically meaningful biofilm growth prevention (median absorbance was 0.2585 [IQR = 0.1235] vs control 0.395 [IQR = 0.218]; p < 0.001; biofilm reduction was 62%).ConclusionsWe advocate that apart from the well-established preventative measures for MRSA carriers, loading implants with bioresorbable Resomer® vancomycin-supplemented coating may decrease the incidence of early post-op surgical site infections with titanium implants. Of note, the payoff between localized toxicity and antibiofilm efficacy should be considered when loading polymers with highly concentrated antimicrobial agents.

Enhanced thermal and electrical properties of hybrid polymer composites containing Al2O3 microspheres and nanowires

Thermal interface materials efficiently transfer heat from high-temperature electronic devices to heat management components to alleviate the overheating that deteriorates component lifetimes of electronic devices. Recently, high-performance polymer composites, made of polymer matrices and thermally conducting fillers, have been actively researched due to their low densities and controllable properties. However, the conventional polymer composites produced by mixing methods of homogeneous fillers have significantly low percolation and poor heat dispersion, which afford reduced mechanical and thermal performances. Herein we propose a strategy for fabricating epoxy composites that provide good electrical insulation and enhanced thermal conductivity using a combination of heterogeneous Al2O3 fillers. The epoxy composites were prepared by using a hybrid filler system comprising microspheres and nanowires, which were fabricated by spray drying and hydrothermal methods, respectively. The use of these two filler components produces a continuous network of fillers throughout the polymer matrix. The thermal conductivity of the hybrid composite is enhanced by 107.9% compared to that of the composite containing only microspheres at the same filler loading (30 wt%). Additionally, the epoxy composites produced with the hybrid filler system provide enhanced electrical insulation (with a dielectric constant of 3.5 at 1 kHz). This hybrid composite approach has the potential to be applied with a wide range of polymers and fillers for use in diverse applications (e.g., wearable devices and electrical vehicles).

Structure and Dynamics in Self-Healing Polymer Electrolytes Based on PVDF-HFP for Battery Applications

Lithium dendrite formation is a key limitation in rechargeable Li metal batteries. Here we report on a novel polymer electrolyte with self-healing capabilities, consisting of PVdF-HFP membranes imbibed with an ionic liquid electrolyte EMIM-TFSI + LiTFSI and mechanically reinforced by alumina nanowires. Similar membranes were reported to have self-healing capability via resistance to dendrite formation at the electrode-electrolyte interface.1 We have investigated the structure and dynamics in these membranes by nuclear magnetic resonance (NMR). Double resonance and 2D NMR methods show that the EMIM cation interacts with CF3 group present in HFP, forming an ion-dipole association which may be related to the desired self-healing properties. Moreover, addition of alumina nanowires has been reported2 to increase the ionic conductivity in the membrane in addition to imparting mechanical strength. We have used pulsed field gradient (PFG) NMR to investigate how alumina nanowire doping into the PVDF-HFP-IL matrix improves the Li+ diffusivity. Additional characterizations such as electron dispersion X-ray (EDX) spectroscopy to study nanowire distribution in the polymer and ionic conductivity measurements, will also be discussed. Keywords: Ionic Liquids, Self-healing, Dendrite formation, PVDF-HFP membranes, NMR spectroscopy, EDX References Chen, T. et al. Ionic liquid-immobilized polymer gel electrolyte with self-healing capability, high ionic conductivity and heat resistance for dendrite-free lithium metal batteries. Nano Energy 54, 17–25 (2018).Kwon, S. J. et al. Influence of Al2O3 Nanowires on Ion Transport in Nanocomposite Solid Polymer Electrolytes. Macromolecules 51, 10194–10201 (2018).

Mechanical and Tribological Performance of Self-Cured Poly Methyl Methacrylate Reinforced by Alumina Nanowires and Zirconia Nanoparticles for Denture Applications

Polymethyl methacrylate (PMMA) is one of the common widely accepted biomaterials in prosthetic dentistry due to its acceptable advantages, since 1937. In the present work, PMMA reinforced with Al2O3 nanowires (Al2O3 NWs) and ZrO2 nanoparticles (ZrO2 NPs) were fabricated by a self-curing method. Mechanical and tribological tests were conducted to study the effect of nanofillers on the mechanical and tribological performance of PMMA nanocomposites. Compression and microhardness tests, as mechanical tests, were accomplished to estimate the elastic modulus and microhardness number of the present nanocomposites. Also, tribological properties of unfilled PMMA and its nanocomposites were realized by pin-on-disk tester under dry sliding conditions. Wear test was conducted at room temperature under applied loads of 10, 20, 30, 40, and 50 N at a constant sliding speed and distance of 1.256 m/s and 226 m, respectively to study wear rate and coefficient of friction (COF) of the nanocomposites. Experimental results revealed that the elastic modulus, microhardness, wear rate, and COF were enhanced with increasing nanofiller content up to 0.5 and 0.7 wt. % of Al2O3 NWs and ZrO2 NPs, respectively. Also, wear rate increased with increasing applied loads up to 50 N, while COF decreased with increasing applied loads up to 40 N. Finally, specimens� worn surfaces were examined and imaged using scanning electron microscope (SEM).

Influence of Abrasive Water Jet Machining Parameters on Hybrid Polymer Composite

In this current research study, the holes are drilled in the hybrid composite reinforced with Ni–P-coated glass fiber (GF) and Al2O3 nanowires via abrasive water jet (AWJ) machining process. The input process parameters such as jet pressure, traverse speed, and concentration of abrasive on the delamination characteristic both at the inlet and at the exit sides of the drilled holes are investigated and optimized for the minimum delamination and fiber pullouts. The experiments are conducted using Taguchi’s L25 orthogonal arrays, and the input process parameters are optimized for lesser delamination at both sides together by grey relational analysis. From the experimental results, it is clear that the abrasive flow rate has significantly effect on the delamination characteristics followed by abrasive water jet pressure and the traverse speed. Grey relational technique is used for optimizing multiple responses (delamination at the inlet and exit) simultaneously. The morphological analysis was been carried out using scanning electron microscope (SEM) to determine the wall quality of the drilled holes. From the experimental analysis, it was found that the machined surfaces were free from delamination to an extent at optimized conditions (the mass flow rate of 350 gm/min, jet pressure of 3000 Bar and traverse speed of 800 mm/min, respectively), which leads to minimal delamination both at the entry and at exit side of the machined hole as compared with the holes drilled by conventional machining process.

Effect of Al2O3 with Different Nanostructures on the Insulating Properties of Epoxy-Based Composites.

High thermal conductivity insulating dielectrics with good electrical properties have received widespread attention due to the continuous development of power systems and power electronic technologies. In this paper, the effects of differently structured nano alumina fillers on the thermal conductivity and insulating properties of polymer-based composites were studied. It was found that all three types of Al2O3 nano-fillers enhanced the thermal conductivity of the composites, and the thermal conductivity increased more dramatically with increasing filler particle size. It is worth noting that Al2O3 nanowires (NWs) exhibited the most significant improvement in thermal conductivity. The volume resistivity of the composites first increased and then decreased with increasing mass fraction of fillers, and Al2O3 nanoplates (NPLs) showed the most significant improvement in the insulation performance of the composites. The dielectric constants of the composites increased with increasing mass fraction of fillers, while the dielectric losses first decreased and then increased with the same trend, yet the mass fractions of fillers for the three materials were different when the dielectric loss reached a minimum. In addition, all three types of filler increased the AC breakdown strength of the composites, but Al2O3-NPLs showed the most significant improvement on the breakdown performance of the composites.

Liquid Phase Hydrogenation of Pharmaceutical Interest Nitroarenes over Gold-Supported Alumina Nanowires Catalysts.

In this work, Au nanoparticles, supported in Al2O3 nanowires (ANW) modified with (3-aminopropyl)trimethoxysilane were synthetized, for their use as catalysts in the hydrogenation reaction of 4-(2-fluoro-4-nitrophenyl)-morpholine and 4-(4-nitrophenyl)morpholin-3-one. ANW was obtained by hydrothermal techniques and the metal was incorporated by the reduction of the precursor with NaBH4 posterior to superficial modification. The catalysts were prepared at different metal loadings and were characterized by different techniques. The characterization revealed structured materials in the form of nanowires and a successful superficial modification. All catalysts show that Au is in a reduced state and the shape of the nanoparticles is spherical, with high metal dispersion and size distributions from 3.7 to 4.6 nm. The different systems supported in modified-ANW were active and selective in the hydrogenation reaction of both substrates, finding for all catalytic systems a selectivity of almost 100% to the aromatic amine. Catalytic data showed pseudo first-order kinetics with respect to the substrate for all experimental conditions used in this work. The solvent plays an important role in the activity and selectivity of the catalyst, where the highest efficiency and operational stability was achieved when ethanol was used as the solvent.

Scalable, safe, high-rate supercapacitor separators based on the Al2O3 nanowire Polyvinyl butyral nonwoven membranes

High-performance supercapacitor nonwoven separators based on polyvinyl butyral (PVB) with uniformly distributed Al2O3 nanowires (NW) fillers (up to 40 wt %) have been developed using a low-cost casting (stir-pour-dry) technique utilized under ambient conditions for the first time. These novel nonwoven separators with highly porous network demonstrated tensile strength of >30 MPa, extremely high electrolyte absorption (>200 wt. %), low-to-no swelling behavior and stable electrochemical performance, substantially exceeding that of analogous cells with commercial separators. Thermal properties of the produced separators were also exceptional with >15 MPa of ultimate strength, high flexibility and minimal thermal shrinkage maintained at temperatures as high as 200 °C. The one-dimensional (1D) ceramic nanofillers improved PVB's mechanical and thermal properties and enabled formation of highly porous membranes with self-organized nanopores and high ionic conductivity of up to 13.5 mS/cm in 1 M Na2SO4 aqueous electrolyte. This simple and innovative method and separator design is attractive for manufacturing of high-strength, low-cost and flexible separators and suitable for various polymers-ceramic nonwoven compositions for fast charging, high-power and safe electrochemical capacitors, hybrid devices and batteries.

Preparation of Al2O3 nanowires on 7YSZ thermal barrier coatings against CMAS corrosion

Abstract The commonly-employed material for thermal barrier coatings (TBCs) is 7 wt.%Y2O3–ZrO2 (7YSZ), generally deposited by electron beam-physical vapor deposition (EB-PVD). Due to the increasing demand for higher operating temperature in aero-derivative gas turbines, a lot of effort has been made to prevent the premature failure of columnar 7YSZ TBCs, which is induced by the microstructure degradation, sintering and spallation after the deposition of infiltrated siliceous mineral (consisting of calcium–magnesium–aluminum–silicate (CaO–MgO–Al2O3–SiO2, i.e., CMAS)). A new method called Al-modification for columnar 7YSZ TBCs against CMAS corrosion was present. The Al film was magnetron-sputtered on the surface of the columnar 7YSZ TBCs, followed by performing vacuum heat treatment of the Al-deposited TBCs. During the heat treatment, the molten Al reacted with ZrO2 to form α-Al2O3 overlay that effectively hindered CMAS infiltration. Moreover, the Al film could evaporate and re-nucleate, leading to the generation of Al2O3 nanowires, which further restrained the moving of molten CMAS.

Modification of poly(vinylidene fluoride) membranes with aluminum oxide nanowires and graphene oxide nanosheets for oil–water separation

ABSTRACTTo improve the hydrophilic and oleophobic properties of membrane, we adopted aluminum oxide (Al2O3) nanowires and graphene oxide (GO) nanosheets to modify poly(vinylidene fluoride) (PVDF) membranes. The experimental results show that the intercalation of Al2O3 nanowires between GO nanosheets effectively improved the roughness of the GO–Al2O3–PVDF membrane, and the permeability of the membrane with an optimal mass ratio of Al2O3 to GO of 7.5 was 31 times that of the GO–PVDF membrane. Furthermore, the addition of Al2O3 nanowires significantly enhanced both the hydrophilic and oleophobic properties of the GO–Al2O3–PVDF membrane. On the basis of the extended Derjaguin–Landau–Verwey–Overbeek theory, the energy barriers between the oil droplets and GO–PVDF and GO–Al2O3–PVDF membranes were 0.63 and 0.9 KT, respectively; this indicated improvements in the anti‐oil‐fouling ability of the GO–Al2O3–PVDF membranes. We also found that both the GO–PVDF and GO–Al2O3–PVDF membranes had great oil–water separation rates (97.9 and 99.4%, respectively) with an initial oil concentration of 200 mg/L. The findings of this study show that the GO–Al2O3–PVDF membrane is a promising oil–water separation membrane, and further investigation of the cleaning procedure is needed to promote its practical application in oil–water separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47493.

Characterizing the surface forces between two individual nanowires using optical microscopy based nanomanipulation

The adhesion and friction between two Al2O3 nanowires (NWs) was characterized by the use of optical microscopy based nanomanipulation, with which peeling, shearing and sliding was performed. The elastically deformed shape of the NWs during peeling and shearing was used to calculate the adhesion and frictional forces; force sensing was not required. The obtained adhesion stress between two Al2O3 NWs varied from 0.14 to 0.25 MPa, lower than that observed for carbon nanotube junctions, and was attributed to van der Waals attraction. Stick-slip was observed during the shearing and sliding of two NWs, and was the consequence of discrete contact between surface asperities. The obtained static and kinetic frictional stresses varied from 0.7 to 1.3 MPa and 0.4 to 0.8 MPa, respectively; significantly greater than the obtained adhesion stress.

Growth Behavior Evolution of Al2O3 Deposited on HOPG by Atomic Layer Deposition

Abstract Al2O3 dielectrics were fabricated on highly ordered pyrolytic graphite (HOPG) by atomic layer deposition (ALD) and the effects of growth temperatures and number of ALD cycles on growth behaviors were studied. It is found that Al2O3 preferentially grows along the step edges which promote the formation of Al2O3 nanowires at the initial stage. Al2O3 nanowires can exist after 100 ALD cycles at 50, 150, and 200 °C, but discontinuous Al2O3 thin films rather than nanowires are evidenced at 100 °C. Moreover, the Al2O3 layers evolve into continuous thin films with increasing number of ALD cycles. It suggests the growth behavior undergoes a transition from three-dimensional mode to quasi two-dimensional mode with increasing number of ALD cycles. The rates of transition and lateral growth are dependent on growth temperatures. Raman spectra indicate that HOPG maintains undamaged and greatly reserves its original properties after the deposition of Al2O3. The results are of great significance to the fabrication of high-quality dielectric layers on graphene as well as the related devices.

Synthesis of Al2O3 nanowires by heat-treating Al4O4C in a carbon-containing environment

A novel route was developed for the synthesis of Al2O3 nanowires by heat-treating Al4O4C via Si atom doping in a furnace with a carbon heater. The nanowires had dimensions of 20–60nm in diameter and a few hundred microns in length, and were tunable by adjusting the heating temperature. Al2O3 nanowires exhibited a curved, or twisted, structure and the interface of the bending part had a defective microstructure. The study of their growth mechanism indicates that the Al2O3 nanowires grew by a vapour–liquid–solid (VLS) growth process.

Transformation of Bulk Alloys to Oxide Nanowires and Their Use in a Li-ion Battery Separator

One dimensional (1D) nanostructures offer prospects for enhancing electrical, thermal and mechanical properties of a broad range of functional materials and composites, but their synthesis methods, such as catalyst-assisted vapor deposition, physical vapor deposition, hydrothermal synthesis, the use of sacrificial templates and others, are relatively expensive and difficult to scale. Here we demonstrate direct transformation of bulk materials into nanowires at room temperature and ambient pressure without use of catalysts, corrosive or toxic chemicals, or any external stimuli [1]. The nanowire formation proceeds via a minimization of the strain energy at the boundary of chemical transformation reaction front. We show transformation of multi-micron particles of Al alloy and Mg alloy into alkoxide nanowires of tunable dimensions, which are converted into oxide nanowires upon simple heating in air. The reported approach provides opportunities for ultra-low cost large-scale synthesis of 1D materials and membranes. Conventional polymer separators for Li-ion batteries (LIBs) suffer from limited mechanical strength and low thermal stability, which may lead to thermal runaway and cell explosion. We produced flexible, binder-free, nonwoven fabric composed of gamma-Al2O3 nanowires, using a simple tape casting technique followed by a heat treatment in air. The overall morphology of the produced fabric is somewhat similar to that of a paper, where the cellulose fibers are replaced with stronger and stiffer Al2O3 nanowires. Owing to the fibrous nature of thus-produced free-standing films and the small diameter of the Al2O3 nanowires, they exhibit good flexibility. This is in contrast to anodized Al2O3 membranes of comparable thickness that are known to be extremely brittle and difficult to handle. Results of electrolyte wetting tests revealed significantly superior performance of Al2O3 paper compared to commonly used commercial olefin (polypropylene) separator or a cellulose fiber separator. The wetting rate of the Al2O3 separator is significantly higher owing to its polar nature, as determined by both the final wetting area and the speed of etting. Thermal stability tests demonstrate the advantage of having a flexible porous ceramic separator with operating temperatures above 800°C, which is important because of rapid heating to high temperatures that may occur in failing LIBs. In contrast, the most commonly used olefin separators typically start melting at around 120°C and oxidize at around 300°C. Finally, the strength of ceramic fibers is known to exceed that of the olefins, which should allow formation of thinner separators in automotive LIBs without sacrifice of their mechanical properties. [1]. D Lei, J Benson, A Magasinski, G Berdichevsky, G Yushin, Transformation of bulk alloys to oxide nanowires, Science 2017, 355 (6322), 267-271.

The effect of surface texture on the kinetic friction of a nanowire on a substrate

The friction between Al2O3 nanowires and silicon substrates of different surface textures was characterised by use of optical manipulation. It was found that surface textures had significant effect on both the friction and the effective contact area between a nanowire and a substrate. A genetic algorithm was developed to determine the effective contact area between the nanowire and the textured substrate. The frictional force was found to be nearly proportional to the effective contact area, regardless of width, depth, spacing and orientation of the surface textures. Interlocking caused by textured grooves was not observed in this study.

Dynamic mechanical, thermal and wear analysis of Ni-P coated glass fiber/Al₂O₃ nanowire reinforced vinyl ester composite

Hybrid polymer composites nowadays are increasingly used in many engineering products which are subjected to wear, dynamic mechanical and thermal applications. So in the present study, we have investigated the evaluation of dynamic mechanical, thermal and wear properties of vinyl ester hybrid composite strengthened with Ni-P coated E-glass fiber and Al₂O₃ nanowires as reinforcement at different concentrations. Nickel-Phosphorus is plated over the glass fiber substrate by means of the electroless plating method. The best optimum bath composition was determined after many trials and used for the proper plating process. From the outcome of the result, it is clear that the storage modulus has a trend to increase with increase in the concentration of Ni-P coated glass fiber (GF) and further increases when Al₂O₃ nanowires are used as the reinforcement. The glass transition temperature is also shifted to the higher temperature in the process. From the thermogravimetric analysis, it is clear that the thermal stability of the composite steps up with the addition of Al₂O₃ nanowires as fillers and Ni-P/GF as reinforcement. The wear properties are analyzed and the morphology of the coated and worn-out surfaces are studied by means of scanning electron micrographs and optical microscope images.

Synthesis of porous Al2O3/ZrO2 nanocomposites by chemical vapour deposition

ABSTRACTAl2O3/ZrO2 one-dimensional nanocomposite structures were synthesised by chemical vapour deposition using Al2O3 nanowires and a ZrCl4 powder source at a temperature of 800 °C and a pressure of 130 Pa. The samples were characterised using X-ray diffraction, the scanning electron microscopy, the transmission electron microscopy, and N2 adsorption–desorption. The results revealed that Al2O3/ZrO2 composite nanowires coated with surface-embedded ZrO2 nanocrystals were formed and that the ZrO2 macroporous and mesoporous structures changed as the ZrO2 deposition time increased. The pore structure and surface area were also elucidated from the N2 adsorption–desorption measurements.

Alumina nanowire growth by water decomposition and the peritectic reaction of decagonal Al65Cu15Co20 quasicrystals

In this paper, the results of the Al2O3 nanowires' growth through a chemical reaction between Al and water vapor at 1050°C are presented. Our approach is based on two primary considerations. First, at room temperature, the Al65Cu15Co20 alloy is affected by the following mechanism: 2Al (s)+3H2O (g)→Al2O3 (s)+H2 (g). In this reaction, the released hydrogen induces cleavage fracture of the material to form small particles. Second, the Al65Cu15Co20 quasicrystalline phase is transformed on heating to liquid+Al (Cu, Co) cubic phase through a peritectic reaction at 1050°C. The Al-rich liquid then reacts with water vapor, forming Al2O3 nanowires. X-ray diffraction (XRD) analysis shows that the formed nanowires have a hexagonal structure, and infrared analysis further confirms the presence of α-Al2O3 phase in the final products. Transmission electron microscopy observations show that nanoparticles are present at the end of nanowires, suggesting the VLS growth mechanism. Elemental analysis by energy dispersive spectroscopy (EDS) indicates that the particles at the tip of the nanowires are mainly formed by Co and Cu alloying elements and small amounts of Al. Electron microscopy observations showed nanowires with diameters ranging from 20 to 70nm; the average diameter was 37nm and the nanowire lengths were up to several micrometers.

The kinetic friction between a nanowire and a flat substrate measured using nanomanipulation with optical microscopy

The kinetic frictional force between a nanowire and its supporting flat substrate was measured using nanomanipulation with optical microscopy at ambient atmosphere. During testing, the nanowire was pushed at its center point by a sharp tip and thus exhibited an arc shape held by the frictional shear stress (kinetic friction per area). The arc-shaped nanowire slid along the supporting substrate with further pushing. The frictional shear stress was derived from the arc shape of the nanowire based on the theory of elasticity. The frictional shear stresses of Al2O3 nanowires on the Si and SiN substrates were measured to be 2.0 ± 0.2 and 1.5 ± 0.2 MPa, respectively. It was found that the lengths of the nanowires and their angular orientations with the substrate, the arc shapes being formed and the driving mode of the tip had insignificant effects on the measured frictional shear stress.

Charge optimized many-body (COMB) potential for Al2O3 materials, interfaces, and nanostructures

This work presents the development and applications of a new empirical, variable charge potential for Al2O3 systems within the charge optimized many-body (COMB) potential framework. The potential can describe the fundamental physical properties of Al2O3, including cohesive energy, elastic constants, defect formation energies, surface energies and phonon properties of α-Al2O3 comparable to that obtained from experiments and first-principles calculations. The potential is further employed in classical molecular dynamics (MD) simulations to validate and predict the properties of the Al (1 1 1)–Al2O3 (0 0 0 1) interface, tensile properties of Al nanowires, Al2O3 nanowires, Al2O3-covered Al nanowires, and defective Al2O3 nanowires. The results demonstrate that the potential is well-suited to model heterogeneous material systems involving Al and Al2O3. Most importantly, the parameters can be seamlessly coupled with COMB3 parameters for other materials to enable MD simulations of a wide range of heterogeneous material systems.