Advanced Materials Research Vols. 47-50

Abstract: Commercially, multi-walled carbon nanotubes (MWCNTs) production methods are based on the use of transition metal catalysts such as chemical vapor deposition (CVD). Raw MWCNTs usually contain metal catalysts and other carbon impurities. A common route to eliminate these impurities is an acid treatment. In addition, this route induces cutting of MWCNTs which can control the aspect ratio of MWCNTs. The aspect ratio controlled MWCNTs can use many applications such as the electrode material, biological imaging and sensing, etc. In this study, the aspect ratio of MWCNTs was controlled using an acid treatment with a 3:1 concentrated H2SO4/HNO3 mixture by varying the treatment time. Results show that an acid treatment can control the aspect ratio of MWCNTs. The aspect ratio controlled MWCNTs were observed by TEM and Raman spectra.

Abstract: The multiwalled carbon nanotubes (MWCNTs) incorporated organic silk fibroin cryogels were fabricated through sol-gel process of aqueous silk fibroin solution, followed by freeze-drying. The MWCNT incorporated silk fibroin hydrogel was prepared by the regeneration of silk fibroin using an aqueous silk fibroin solution in which MWCNTs were dispersed by in-situ methods. The morphology and microstructure of the silk fibroin network structure were characterized using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The FESEM and TEM images show that the cryogels had three-dimensional network structures and the MWCNTs were well embedded in the network structures of regenerated silk fibroin. The porous properties of the MWCNT incorporated silk fibroin cryogels were investigated by nitrogen adsorption-desorption technique. The MWCNTs increased the proportions of micropores and mesopores in the silk fibroin cryogels when they were introduced in the appropriate amounts.

Abstract: Polyurethane was used as adhesive due to high reactivity, high flexibility, and mechanical properties. Electrically conductive adhesives (ECAs) are an alternative to tin-lead solder in order to provide conductive paths between two electrical device components, which typically consist of a polymeric resin that contributes physical and mechanical properties, and conductive fillers. However, ECAs have low electrical conductivity and unstable network due to large contact points of the few micrometer-sized metal particles. In order to overcome these restrictions, multiwalled carbon nanotubes (MWCNTs) with high aspect ratio and smaller nanometer scale can be used as conductive fillers. In this study, ECAs were based on polyurethane filled with two kinds of fillers, raw MWCNTs and acid treated MWCNTs, respectively. Electrical conductivity was measured by using four-point probe. Morphology and dispersibility of fillers were observed by scanning electron microscopy and transmission electron microscopy.

Abstract: To enhance the electrical conductivity of the electrolyte in a newly-developed dye-sensitized solar cell (DSSC), the Cu@C (metallic copper core in the carbon shell) nanoparticles dispersed in a room temperature ionic liquid (RTIL) (e.g., [bmin][BF6]) has been studied in the present work. By the pulsed-field gradient spin-echo NMR method, the self-diffusion coefficients of cations and anions in the RTIL have been determined. The self-diffusion coefficient of cations is increased by 40% at 300 K. It is also found that the electrical conductivity of the Cu@C dispersed (0.08%) RTIL is increased by 30% (1.96→2.38 ms/cm). It seems that that the nanosize Cu@C dispersed RTIL is a very effective electrolyte especially used in the DSSCs.

Abstract: In the present work, sensing of ethanol on the ZnO thin films doped with Fe (5-50%) have been investigated. Nature of the sensing species in the nanosize Fe-doped ZnO (FeZnO) thin films has also been studied by in situ extended X-ray absorption fine structure (EXAFS) spectroscopy. By XRD, it is found that ZnO and ZnFe2O4 are the main compounds in the ZnO-Fe thin films. The thin film containing 5% of Fe has a high sensitivity (Rair/Rethanol>80) when sensing of ethanol at 300 K. On the contrary, the thin films with Fe fractions of 20-50% have a very low sensitivity to ethanol (Rair/Rethanol<15). In the presence of ethanol, the EXAFS spectra show that the bond distances of Zn-O and Fe-O in the thin films are 1.90 and 1.98 Å, respectively and restored to 1.91 and 1.97 Å in the absence of ethanol.

Abstract: To enhance the efficiency of a newly developing dye-sensitized solar cell (DSSC), Cu@C (7-20 nm) nanoparticles dispersed electrolyte has been studied. Experimentally, the efficiencies (η) of the DSSC are in the range of 2.70-4.09% with a short-circuit photocurrent density (Jsc) of 5.775-9.910 mA/cm2. Interestingly, it is found that addition of 1% of Cu@C (7 nm) nanoparticles in the molten salt (1,2-dimethyl-3-propylimidazolium iodide (DMPII)) conjugated electrolyte leads to an enhancement of 11% in the conversion efficiency (η) of 4.06%. By XANES, about 17-32% of copper in the core of Cu@C are oxidized to Cu2O (10-17%) and CuO (5-17%) in the molten salt in the electrolyte.

Abstract: X-ray absorption near edge structural (XANES) and X-ray absorption fine structural (EXAFS) spectroscopies have been used to study chemical structure of nanosize copper extracted in the channels of MCM-41. The component-fitted XANES spectra show that about 95% of copper are adsorbed on the surfaces of MCM-41 at 298 K. A small amount of nanosize CuO in MCM-41 is also found. The adsorbed copper (Cu(II)(ads)) in the channels of MCM-41 may be oxidized and form nanosize CuO as calcined at 573 and 923 K. By EXAFS, it is observed that the nanosize CuO in MCM-41 possesses a Cu-O bond distance of 1.97 Å with a coordination number (CN) of 2.6, indicating the existence of linear type Cu3O4 cluster. Interestingly, calcinations of the nanosize CuO in MCM-41 at 923 K has led to a formation nanowire-type CuO (in the channels of MCM-41) with a length of 50-100 nm and width of about 5-9 nm.

Abstract: Property of GFRP is naturally dependent on the property of matrix, but receives of temperature effects by external force. Therefore, determination of mechanical property by effect of temperature in GFRP is most crucial factor. In this paper, temperature distribution during crack propagation from temperature change under tensile test was proposed through IR thermography camera. Lock-in thermography method, which is one of technique in IR thermography camera to measure minute change in temperature, was utilized to monitor temperature distribution and change during crack propagation. Method to analyze temperature distribution during crack propagation under tensile test of GFRP via IR thermography camera was suggested. Anisotropy in fiber orientation showed longer fracture time and lower maximum temperature.

Abstract: Viscoelastic properties of 3D fabric reinforced Vinyl Ester composites were studied in different directions using Dynamic Mechanical Thermal Analysis (DMTA). Such materials filled by nanoparticles (silicon carbide) with different concentrations were also investigated. The increases of storage and loss moduli with addition of nanoparticles and with increase of their concentrations were observed. The maximal tangent of the angle of mechanical losses was especially compared at below and over glass transition temperature. Below glass transition temperature the presence of nanoparticles increases storage and loss moduli and loss tangent. These effects achieved maximum at glass transition temperature. Over glass transition, the loss modulus and loss tangent are decreased with increase of the concentration of nanoparticles.

Abstract: In this paper, we use the asymptotic perturbation method to investigate the nonlinear oscillation and chaotic dynamic behavior of a simply supported rectangular plate made of functionally graded materials (FGMs). We assume that the plate is made from a mixture of ceramics and metals with continuously varying compositional profile such that the top surface of the plate is ceramic rich, whereas the bottom surface is metal rich. The equations motion of the FGM plate with two-degree-of-freedom under combined parametrical and external excitations are obtained by using Galerkin’s method. Based on the averaged equation obtained by the asymptotic perturbation method, the phase portrait and waveform are used to analyze the periodic and chaotic motions. It is found that the FGM plate exhibits chaotic motions under certain circumstances.