On the characterisation of syntactic foam core sandwich composites for compressive properties

Sandwich structures, especially those with honeycomb and grid structures as the core material, are very commonly employed in aircraft structures. There is an increasing use of closed-pore rigid syntactic foams as core materials in sandwich constructions because they possess a number of favourable properties. The syntactic foams, owing to their structure and formation, behave differently under compression compared to other traditionally used core materials. In the present study, therefore, syntactic foam core sandwich constructions are evaluated for their behaviour under compression in both edgewise and flatwise orientations. Further, the work characterises the relative performance of two sets of sandwich materials, one containing glass-epoxy and the other, glass/carbon hybrid-epoxy skins. As non-standard geometry test specimens were involved, only a comparative evaluation was contemplated in this approach. The experiments indicate that the nature of the reinforcement fabric in the skin has a bearing on the test results in edgewise orientation. Thus, the tendency towards initiation of vertical crack in the central plane of the core material, which is a typical fracture event in this kind of material, was found to occur after a delay for the specimens containing the glass fabric in the skin. Attempts are made to establish the correlation between observations made on the test specimen visually during the course of testing and the post-compression microscopic examinations of the fracture features.

Dielectric properties of novel PVA/ZnO hybrid nanocomposite films

In this study, the dielectric properties of PVA/ZnO nanocomposites films were evaluated. The composites were prepared by a solution casting technique. The dispersion and functionalization of the ZnO nanoparticles in the composite films were characterized by spectroscopic technique. The surface morphology of the PVA/ZnO nanocomposites films were elucidated using AFM. The charge transport properties were evaluated based on the dielectric and impedance spectroscopy techniques. Low ZnO loading composite shows low dielectric value at higher frequency and behaves as a lossless material. The complex impedance spectra suggest the change in conductivity, due to the change in bulk resistance of the materials and less relaxation time. Thus, all PVA/ZnO nanocomposites behave as lossless materials above 10(6) Hz indicating the composites are useful in microwave application. (c) 2012 Elsevier Ltd. All rights reserved.

Polyvinylbutyral based hybrid organic/inorganic films as a moisture barrier material

Flexible and thermally stable, freestanding hybrid organic/inorganic based polymer-composite films have been fabricated using a simple solution casting method. Polyvinylbutyral and amine functionalized mesoporous silica were used to synthesize the composite. An additional polyol-''tripentaerythritol''-component was also used to increase the -OH group content in the composite matrix. The moisture permeability of the composites was investigated by following a calcium degradation test protocol. This showed a reduction in the moisture permeability with the increase in functionalized silica loadings in the matrix. A reduction in permeability was observed for the composites as compared to the neat polymer film. The thermal and mechanical properties of these composites were also investigated by various techniques like thermogravimetric analysis, differential scanning calorimetry, tensile experiments, and dynamic mechanical analysis. It was observed that these properties detonate with the increase in the functionalized silica content and hence an optimized loading is required in order to retain critical properties. This deterioration is due to the aggregation of the fillers in the matrix. Furthermore, the films were used to encapsulate P3HT (poly 3 hexyl thiophene) based organic Schottky structured diodes, and the diode characteristics under accelerated aging conditions were studied. The weathered diodes, encapsulated with composite film showed an improvement in the lifetime as compared to neat polymer film. The initial investigation of these films suggests that they can be used as a moisture barrier layer for organic electronics encapsulation application.

Impedance spectroscopy of novel hybrid composite films of polyvinylbutyral (PVB)/functionalized mesoporous silica

Polyvinyl butyral/functionalized mesoporous silica hybrid composite films have been fabricated by solution casting technique with various weight percentages of functionalized silica. A polyol (tripentaerythritol-electron rich component), which acts as an electron donor to the polymer backbone, was added to enhance the conductivity. The prepared composites were characterized by Fourier transformed infrared spectroscopy and the morphology was evaluated by scanning electron microscopy. Dielectric properties of these freestanding composites were studied using the two-probe method. The dielectric constant and impedance value decreased with the increase in applied frequency as well as with the increase in functionalized silica content in the polyvinyl butyral matrix. An increase in conductivity of the PVB/functionalized silica composites was also observed. (C) 2013 Elsevier Ltd. All rights reserved.

Using heat treatment effects and EBSD analysis to tailor microstructure of hybrid Mg nanocomposite for enhanced overall mechanical response

In this study, a detailed investigation on the effect of heat treatment on the microstructural characteristics, texture evolution and mechanical properties of Mg-(5.6Ti+2.5B(4)C)(BM) hybrid nanocomposite is presented. Optimised heat treatment parameters, namely, heat treatment temperature and heat treatment time, were first identified through grain size and microhardness measurements. Initially, heat treatment of composites was conducted at temperature range between 100 and 300 degrees C for 1 h. Based on optical microscopic analysis and microhardness measurements, it was evident that significant grain growth and reduction in microhardness occurred for temperatures > 200 degrees C. The cutoff temperature that caused significant grain growth/matrix softening was thus identified. Second, at constant temperature (200 degrees C), the effect of variation of heat treatment time was carried out (ranging between 1 and 5 h) so as to identify the range wherein increase in average grain size and reduction in microhardness occurred. Furthering the study, the effect of optimised heat treatment parameters (200 degrees C, 5 h) on the microstructural texture evolution and hence, on the tensile and compressive properties of the Mg-(5.6Ti+2.5B(4)C)(BM) hybrid nanocomposite was carried out. From electron backscattered diffraction (EBSD) analysis, it was identified that the optimised heat treatment resulted in recrystallisation and residual stress relaxation, as evident from the presence of similar to 87% strain free grains, when compared to that observed in the non-heat treated/as extruded condition (i.e. 2.2 times greater than in the as extruded condition). For the heat treated composite, under both tensile and compressive loads, a significant improvement in fracture strain values (similar to 60% increase) was observed when compared to that of the non-heat treated counterpart, with similar to 20% reduction in yield strength. Based on structure-property correlation, the change in mechanical characteristics is identified to be due to: (1) the presence of less stressed matrix/reinforcement interface due to the relief of residual stresses and (2) texture weakening due to matrix recrystallisation effects, both arising due to heat treatment.

Strontium eluting graphene hybrid nanoparticles augment osteogenesis in a 3D tissue scaffold

The objective of this work was to prepare hybrid nanoparticles of graphene sheets decorated with strontium metallic nanoparticles and demonstrate their advantages in bone tissue engineering. Strontium-decorated reduced graphene oxide (RGO_Sr) hybrid nanoparticles were synthesized by the facile reduction of graphene oxide and strontium nitrate. X-ray diffraction, transmission electron microscopy, and atomic force microscopy revealed that the hybrid particles were composed of RGO sheets decorated with 200-300 nm metallic strontium particles. Thermal gravimetric analysis further confirmed the composition of the hybrid particles as 22 wt% of strontium. Macroporous tissue scaffolds were prepared by incorporating RGO_Sr particles in poly(epsilon-caprolactone) (PCL). The PCL/RGO_Sr scaffolds were found to elute strontium ions in aqueous medium. Osteoblast proliferation and differentiation was significantly higher in the PCL scaffolds containing the RGO_Sr particles in contrast to neat PCL and PCL/RGO scaffolds. The increased biological activity can be attributed to the release of strontium ions from the hybrid nanoparticles. This study demonstrates that composites prepared using hybrid nanoparticles that elute strontium ions can be used to prepare multifunctional scaffolds with good mechanical and osteoinductive properties. These findings have important implications for designing the next generation of biomaterials for use in tissue regeneration.

Size-dependent inelastic behavior of particle-reinforced metal-matrix composites

The strengthening behavior of particle-reinforced metal-matrix composites (MMCp) is primarily attributed to the dislocation strengthening effect and the load-transfer effect. To account for these two effects in a unified way, a new hybrid approach is developed in this paper by incorporating the geometrically necessary dislocation strengthening effect into the incremental micromechanical scheme. By making use of this hybrid approach, the particle-size-dependent inelastic deformation behavior of MMCp is given. Some comparisons with the available experimental results demonstrate that the present approach is satisfactory.

Moderate speed impact damage to 2D-braided glass-carbon composites

Hybrid glass-carbon 2D braided composites with varying carbon contents are impacted using a gas gun by impactors of masses 12.5 and 44.5. g, at impact energies up to 50. J. The damage area detected by ultrasound C-scan is found to increase roughly linearly with impact energy, and is larger for the lighter impactor at the same impact energy. The area of whitening of the glass tows on the distal side corresponds with the measured C-scan damage area. X-ray imaging shows more intense damage, at the same impact energy, for a higher-mass impactor. Braids with more glass content have a modest increase in density, decrease in modulus, and reduction in the C-scan area and dent depth at the impact site, particularly at the higher impact energies. Impact damage is found to reduce significantly the compressive strength, giving up to a 26% reduction at the maximum impact energy. © 2012 Elsevier Ltd.

Physical properties of a hybrid and a nanohybrid dental light-cured resin composite.

This work was aimed at the study of some physical properties of two current light-cured dental resin composites, Rok (hybrid) and Ice (nanohydrid). As filler they both contain strontium aluminosilicate particles, however, with different size distribution, 40 nm-2.5 mum for Rok and 10 nm-1 mum for Ice. The resin matrix of Rok consists of UDMA, that of Ice of UDMA, Bis-EMA and TEGDMA. Degree of conversion was determined by FT-IR analysis. The flexural strength and modulus were measured using a three-point bending set-up according to the ISO-4049 specification. Sorption, solubility and volumetric change were measured after storage of composites in water or ethanol/water (75 vol%) for 1 day, 7 or 30 days. Thermogravimetric analysis was performed in air and nitrogen atmosphere from 30 to 700 degrees C. Surface roughness and morphology of the composites was studied by atomic force microscopy (AFM). The degree of conversion was found to be 56.9% for Rok and 61.0% for Ice. The flexural strength of Rok does not significantly differ from that of Ice, while the flexural modulus of Rok is higher than that of Ice. The flexural strengths of Rok and Ice did not show any significant change after immersion in water or ethanol solution for 30 days. The flexural modulus of Rok and Ice did not show any significant change either after immersion in water for 30 days, while it decreased significantly, even after 1 day immersion, in ethanol solution. Ice sorbed a higher amount of water and ethanol solution than Rok and showed a higher volume increase. Thermogravimetric analysis showed that Rok contains about 80 wt% inorganic filler and Ice about 75 wt%.

Gold/platinum hybrid nanoparticles supported on multiwalled carbon nanotube/silica coaxial nanocables: Preparation and application as electrocatalysts for oxygen reduction

A simple approach combining sonication and sol-gel chemistry was employed to synthesize silica coated carbon nanotube (CNTs) coaxial nanocables. It was found that a homogeneous silica layer can be coated on the surface of the CNTs. This method is simple, rapid, and reproducible. Furthermore, gold nanoparticle supported coaxial nanocables were facilely obtained using amino-functionalized silica as the interlinker. Furthermore, to reduce the cost of Pt in fuel cells, designing a Pt shell on the surface of a noble metal such as gold or silver is necessary. High-density gold/platinum hybrid nanoparticles were located on the surface of I-D coaxial nanocables with high surface-to-volume ratios. It was found that this hybrid nanomaterial exhibits a high electrocatalytic activity for enhancing oxygen reduction (low overpotential associated with the oxygen reduction reaction and almost four-electron electroreduction of dioxygen to water).

A novel hybrid nanostructure based on SiO2@carbon nanotube coaxial nanocable

We present a simple, generally applicable procedure for obtaining diameter-controlled SiO2@ carbon nanotubes (CNTs) coaxial nanocables. These coaxial nanocables with high solubility in polar solvents, have been used as functional templates for assembling CNTs/Au nanorods heterogeneous nanostructures to form multifunctional assembly system. These hybrid nanostructures may find applications in nanoelectronics, photonics, and nanodevices.

Construction of metal nanoparticle/multiwalled carbon nanotube hybrid nanostructures providing the most accessible reaction sites

Functionalized multiwalled carbon nanotubes (MWNTs) were selected as cross-linkers to construct three-dimensional (3D) porous nanoparticle/MWNT hybrid nanostructures by "bottom-up'' self-assembly. The resultant 3D hybrid nanostructure was different from that of metal nanoparticle multilayer assemblies prepared by traditional routes using small molecules or polymers as cross-linkers. The rigidity of the MWNTs resulted in only partial coverage of the nanoparticle surfaces between the linkers during the growth of multilayer film, providing more accessible surfaces to allow target molecules to adsorb on to and react with. HRP was used as a simple model to study the porosity of this assembly.

Synthesis and properties of a novel isomeric polyimide/SiO2 hybrid material

A novel isomeric polyimide/SiO2 hybrid material was successfully prepared through sol-gel technique, and its structure, thermal properties and nano-indenter properties were investigated. First, 3-[(4-phenylethynyl)phthalimide]propyl triethoxysilane (PEIPTES) was successfully synthesized, its structure was characterized by elemental analysis, FT-IR and C-13 NMR. The researches on solubility and thermal properties of PEIPTES show that it can be used for modifying nano-SiO2 precursor. Nano-SiO2 precursor was synthesized by tetraethoxysilane (TECS) through sol-gel technique. Then the PEIPTES solution and the nano-SiO2 precursor were mixed for 6 h to let the PEIPTES molecules react with the nano-SiO2 precursor, and modified nano-SiO2 precursor was obtained. The modified reaction was confirmed by the analyses of FT-IR. At last, isomeric polyimide/SiO2 hybrid material was produced by using isomeric polyimide resin solution and the modified nano-SiO2 precursor after heat treatment process. The structure analysis by SEM indicated that SiO2 particles dispersed in isomeric polyimide matrix homogeneously with nanoscale. Thermogravimetric analyzer, dynamic mechanical thermal analyzer and nano-indenter XP was employed to detect the properties of the materials, the results demonstrated that isomeric polyimide/SiO2 hybrid material has much better thermal properties and nano-indenter properties than those of isomeric polyimide.

Thionine-interlinked multi-walled carbon nanotube/gold nanoparticle composites

Multi-walled carbon nanotube (MWCNT)/thionine/gold nanoparticle composites were prepared by binding gold nanoparticles to the surfaces of thionine-coated carbon nanotubes. TEM images show gold nanoparticles distributed uniformly on nanotube walls and ends. UV-Vis, Raman, FT-IR, and zeta potential measurements were used to examine the properties of the resulting products. The composites demonstrate significant electrocatalytic activity for oxygen reduction. Although only gold nanoparticles were investigated here, the method could be easily extended to attach other metallic nanoparticles to the sidewalls of carbon nanotubes.