Properties and characterization of ([Mengkuang leaf fiber]‐filled ethylene vinyl acetate)/(natural rubber) blend: Effects of blending sequences and mengkuang leaf fiber loading

(Ethylene vinyl acetate [EVA])/(natural rubber [NR])/(Mengkuang leaf fiber) (MLF) thermoplastic elastomer composites were prepared by using three different blending sequences in an internal mixer. The blending sequences studied were (i) B1: NR was added followed by MLF into the molten EVA; (ii) B2: MLF was added followed by NR into the molten EVA; (iii) B3: MLF was added followed by EVA into the molten NR. The effect of different blending sequences and fiber loadings from 10 to 40 parts by weight per hundred parts of resin on the torque development, tensile properties, thermal degradation, and morphology of EVA/NR/MLF composites was studied. Of the blending sequences investigated, the B1 system is considered the best method for the preparation of EVA/NR/MLF composites. The B1 system produces composites with lower stabilization torque, higher tensile strength, and better thermal stability compared with other systems. At 40 parts by weight per hundred parts of resin of MLF loading, the tensile strength of the composite prepared by using the B1 system was 15% higher than that of B2 system composites, and 8% higher than that of the B3 system. Scanning electron micrographs of the tensile fracture surfaces indicated this system also had good fiber dispersion in the EVA/NR matrix. An increase in MLF loading resulted in an increase of the values of the stabilization torque and the Young's modulus, but a decrease in values of the tensile strength, the elongation at break, and the thermal stability of the composites. Scanning electron microscopy revealed increased fiber pullout in the composites as the loading increased. J. VINYL ADDIT. TECHNOL., 24:109–115, 2018. © 2016 Society of Plastics Engineers     

Investigation of Ta2O5/SiO2/4H-SiC MIS capacitors

Tantalum pentoxide (Ta₂O₅) deposited by pulsed DC magnetron sputtering technique as the gate dielectric for 4H-SiC based metal-insulator-semiconductor (MIS) structure has been investigated. A rectifying current-voltage characteristic was observed, with the injection of current occurred when a positive DC bias was applied to the gate electrode with respect to the n type 4H-SiC substrate. This undesirable behavior is attributed to the relatively small band gap of Ta₂O₅ of around 4.3 eV, resulting in a small band offset between the 4H-SiC and Ta₂O₅. To overcome this problem, a thin thermal silicon oxide layer was introduced between Ta₂O₅ and 4H-SiC. This has substantially reduced the leakage current through the MIS structure. Further improvement was obtained by annealing the Ta₂O₅ at 900 °C in oxygen. The annealing has also reduced the effective charge in the dielectric film, as deduced from high frequency C-V measurements of the Ta₂O₅/SiO₂/4H-SiC capacitors.     

Seedless growth of zinc oxide flower-shaped structures on multilayer graphene by electrochemical deposition

A seedless growth of zinc oxide (ZnO) structures on multilayer (ML) graphene by electrochemical deposition without any pre-deposited ZnO seed layer or metal catalyst was studied. A high density of a mixture of vertically aligned/non-aligned ZnO rods and flower-shaped structures was obtained. ML graphene seems to generate the formation of flower-shaped structures due to the stacking boundaries. The nucleation of ZnO seems to be promoted at the stacking edges of ML graphene with the increase of applied current density, resulting in the formation of flower-shaped structures. The diameters of the rods/flower-shaped structures also increase with the applied current density. ZnO rods/flower-shaped structures with high aspect ratio over 5.0 and good crystallinity were obtained at the applied current densities of −0.5 and −1.0 mA/cm². The growth mechanism was proposed. The growth involves the formation of ZnO nucleation below 80°C and the enhancement of the growth of vertically non-aligned rods and flower-shaped structures at 80°C. Such ZnO/graphene hybrid structure provides several potential applications in sensing devices.     

DGEBA‐grafted polyaniline: Synthesis,characterization and thermal properties

The utilization of conducting emeraldine salt (PANI‐ES) and intrinsic leucoemeraldine polyaniline (PANI‐LEB) in the synthesis of DGEBA‐grafted PANI via anionic copolymerization is described. The structures of copolymers obtained were characterized by FTIR, ¹³C and ¹H NMR. The extent of grafting was verified by THF Soxhlet (solvent extraction). The thermal properties of these new copolymers were described and their conductivities were reported. Results obtained indicated that the graft copolymer exhibited higher electrical and thermal conductivities than that of the blend counterpart. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of partial replacement of chitosan with halloysite nanotubes on the properties of polylactic acid hybrid biocomposites

In this study, hybrid chitosan/halloysite nanotubes (Cs/HNTs) reinforced polylactic acid (PLA) were prepared via melt compounding and compression molding techniques. In the fabrication of PLA/Cs/HNTs hybrid biocomposites, the partial replacement of Cs with HNTs was performed at filler loading of 2.5 parts per hundred parts of polymer (php), proceeding from the highest tensile strength of PLA/Cs obtained in our previous study. Cs was partially replaced with different HNTs loadings (0.5, 1, 1.5, 2, and 2.5) php and its effects on the functional group, thermal, tensile, morphological, and water absorption properties were investigated systematically. The results revealed that the combined loading of 1 php Cs and 1.5 php HNTs hybrid fillers into PLA showed the best performance in all properties. Fourier transform infrared spectroscopy (FTIR) analysis indicated that the siloxane (Si O) group of HNTs had chemically interacted with the amine group of Cs. The thermal analysis demonstrated that partial replacement of Cs with 1.5 php HNTs improved the thermal stability of PLA/2.5Cs/0HNTs biocomposite by ~12%. Yet, the percentage of crystallinity (χ_c) reduced with HNTs addition due to the phase adhesion improvement. Moreover, PLA/1Cs/1.5HNTs hybrid biocomposites showed the highest tensile strength and elongation at break of 59 MPa and 2.72%, respectively. This correlated with the uniform dispersion and better interfacial adhesion between Cs/HNTs fillers in the PLA matrix, as confirmed by the field emission scanning electron microscopy (FESEM). In addition, partial replacement of Cs with HNTs exhibited a lower water absorption percentage, which suggested the advantage of hybrid fillers to reduce water uptake, and is beneficial in a wide range of applications.     

Field emission from patterned carbon nanotube emitters produced by microwave plasma chemical vapor deposition

Large area carbon nanotube patterns were fabricated by microwave plasma chemical vapor deposition. The carbon nanotubes were grown on pre-patterned catalyst films. Scanning electron microscopy and Raman spectroscopy were used to characterize the structure of the carbon nanotubes. The carbon nanotubes were very uniform and approximately 100 nm in diameter. The Raman spectrum shows a good graphitization for the carbon nanotubes. Aligned growth was found on the pattern line area. Field emission characteristics of the patterns were characterized. A threshold field of 2.0 V/μm and emission current density of 1.1 mA/cm² at 3.6 V/μm were achieved. A clear and stable image showing the patterns were obtained.     

Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation

We report the seed/catalyst-free growth of ZnO on multilayer graphene by thermal evaporation of Zn in the presence of O₂ gas. The effects of substrate temperatures were studied. The changes of morphologies were very significant where the grown ZnO structures show three different structures, i.e., nanoclusters, nanorods, and thin films at 600°C, 800°C, and 1,000°C, respectively. High-density vertically aligned ZnO nanorods comparable to other methods were obtained. A growth mechanism was proposed based on the obtained results. The ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics.     

The role of oxygen in electron cyclotron resonance etching of silicon carbide

The electron cyclotron resonance (ECR) etching of silicon carbide (SiC) was studied using SF₆ + O₂ based plasma. The role of O₂ was studied by varying the O₂ flow rate while keeping the total gas flow constant. It was found that oxygen enhances the etch rate at low O₂ fraction through releasing more fluorine atoms, while lowers the etch rate at high O₂ fraction by diluting fluorine atoms and forming an oxide-like layer. The etched surface roughness was found to be affected by the surface oxidation and oxygen ion related physical ion bombardment. The role of oxygen in chemical etching of carbon was found to be insignificant. In general, the etched surface is smooth and free of micromasking effect that can arise from Al contamination and C rich layer.     

Interfacial energy dissipation in a cellulose nanowhisker composite

Cyclic tensile and compressive deformation is applied to cellulose nanowhisker-epoxy resin based model nanocomposites. The molecular deformation of the cellulose nanowhiskers within the epoxy resin matrix is followed using a Raman spectroscopy technique, whereby shifts in the position of a band located at ～ 1095 cm(-1) are shown to correlate directly with a breakdown in the interfaces between the resin and the nanowhiskers and between nanowhiskers themselves. A theoretical model is used to determine the dissipation of energy at the interfaces between whiskers and at the whisker-matrix interface. This approach is shown to be useful for interpreting the local micromechanics of these materials by providing a quantitative measure of the quality of the interface.