Advanced Materials Research Vols. 463-464

Abstract: The carbon materials prepared by PVDF carbonization at different temperatures have similar BET surface area and pores volume. The content of fluorine in the carbons decreased with the carbonization temperature from 1.46% (atm %) at 600°C to 0.18 %( atm %) at 1000°C. The first cycle specific capacity and the initial coulombic efficiency decreases with the decrease of fluorine content in the samples. The first cycle discharge capacity decreased from 982 mAh/ g at 600°C to 752 mAh/ g at 1000°C and the initial coulombic efficiency decreased from 31.8% at 600°C to 24% at 1000°C. It is believed that fluorine contained in the carbon materials has a positive effect to improve the electrochemical properties as anode materials for Li-ion batteries.

Abstract: Series of poly (vinyl alcohol)/chitosan (PVA/CS) electrospun nanofibers with different weight ratio of PVA and CS were fabricated by electrospinning method. The surface morphology, diameter, and structure of electrospun nanofibers were investigated by scanning electron microscopy (SEM). As a result of PVA and CS composition measurements, the electrospun nanofibers morphologies were mainly affected by weight ratio of the polymer solution. When increasing the chitosan content in the blend solution, the electrospun nanofibers could hardly form. This result indicates that the electrospun nanofiber formation is enhanced by chitosan content.

Abstract: Nanomaterials such as 1-dimensional nanowires and nanotubes and 2-dimensional graphene are the promising materials for novel device developments due to their unique physical and chemical properties. For field emission applications, nanomaterials are excellent candidate for an electron source by advantages of their small dimensions and high aspect ratios. In this study, we used GaN nanowires as the nanomaterials synthesized by Vapor-Liquid-Solid method. The field emission devices were then fabricated using the general Si microfabrication techniques. Moreover, the field emission properties of the GaN nanowires were characterized using cold field emission theory. It is demonstrated that the fabrication techniques shown in this study are efficient to fabricate field emission devices using nanomaterials.

Abstract: A heterogeneous structured photo electrode using CDS -modified TiO₂ nanotube arrays (TNA) was fabricated. The CDS nano particles were precipitated by immersing TNA into NaS and Cd (ClO4)₂solution, where the number of immersion gave different amount of CDS precipitates. The effect of CDS on the performance of photochemical cell of TNA was evaluated. FESEM, EDS, XRD and UV-Visible were employed to characterize the structures and properties of CDS -modified TNA heterogeneous structure. The water splitting experiments were carried out using these CDS -modified TNA under standard AM 1.5 solar illumination (100mW/cm²>). An optimum hydrogen generation rate of 20.61μmole/cm²>)h (~0.50 ml/cm²>)h) was obtained. It was considered that the smaller band gap of CDS rendered the electrons a rapid transportation to the TiO₂nanotube arrays and the recombination of electron-hole was therefore effectively prevented. In summary, the CDS nano particles were effective in promoting the catalytic effect of TNA for hydrogen production.

Abstract: Vimentin intermediate filament (IF) is one of the major proteins which built the cytoskeleton network alongside with the microtubule and actin filament. Though it was known that the vimentin IF network plays an important role in the mechanical behaviours of cells, it is surprised that its mechanical behaviours are not fully understood to date. The aim of this paper is to study the nanomechanical properties of vimentin IF using the atomic force spectroscopy (AFM) which allows the manipulation and force spectroscopy of filaments. The vimentin intermediate filaments were attached to the APTES (3-aminopropyltriethoxy) functionalized mica which offered better adhesive force. In the force spectroscopy study, the AFM tip was allowed to clamp filaments and then retraced. The force-displacement curve of the process was obtained for analysis. The curves can be grouped into two major groups – sewtooth and plateau. The appearance of sewtooth was more frequent than the plateau. The sudden force changes (jumps from higher to lower force) in sewtooth and plateau curves were also analyzed. It was shown that the partial ruptures which denoted by the jumps favoured small force (~100 pN) and short range (separation of jumps below 25 nm). This result also demonstrated the probability of different modes of partial IF ruptures.

Abstract: The 100Ah Li-ion battery with LiFePO4 material as cathod materails is fabricated by laminated electrode technique. The key preparation techniques of preparating battery is optimized in this paper.The examinations results indicate that it is an effective method to improve electric performance of battery by VGCF addition in the cathode activated materials; Solid phase mixing technique can obviously improve the electrode coating effect and reduce the electrode polarization effect.When the catthod electrode surface density is kept as 2.4 g.dm2-, and pressing density is kept as 2.6 g/cm3-, the largest capacity of the battery is105.56 Ah at the 0.5C discharge current, and the specific capacity of cathod LiFePO4 materials is 135.84mAh/g; There is above 98% capacity retention rate of LiFePO4 battery after 200 cycles at 0.5C discharge current. After the safety examinations including overfilling, short circuit, extrusion and needle-punching, prepared LiFePO4 battery shows its desirable safty performance.

Abstract: Nanoparticles of Cr2O3 were successfully obtained via hydrothermal reduction of CH3OH. The oxidant and chromium source was CrO3. The process needs no stirrer or surfactant and the CrO3 concentration was 0.83mol/L. The obtained products were loosely agglomerated Cr2O3 nanoparticles with the average size of 29 to 79 nm. Influences of reactant ratios and calcination temperatures on the specific surface area and average particle size were discussed. And the morphology of nanoparticles was investigated by use of field-emission scanning electron microscope.

Abstract: In this research, metallic silicon was used as anode material of lithium ion batteries. Electrochemical lithium storage property of metallic silicon was studied which is compared with pure silicon. The results show that for different content of electrical conductors in electrode, the first discharging and charging specific capacity of metallic silicon is similar to pure silicon. The attenuation on capacity of metallic silicon is slower than pure silicon. The lithium storage mechanism of metallic silicon is similar with pure silicon. The testing results of metallic silicon under different charging and discharging rate show that the lithium storage property of metallic silicon is better under lower charging and discharging rate.

Abstract: PMIA is a functional fiber with superior heat-resistance, flame resistance, high temperature dimensional stability and electrical insulation. In PMIA crystal structure, there exist hydrogen bonds between two planes in the crystal and they are arranged in grid. The strong interactions between hydrogen bonds result in a very stable chemical structure of PMIA. Owing to lower internal rotation potential energy than PPTA, PMIA molecular chains are flexible structures and its elastic modulus is in the same level as other flexible macromolecules. In this paper, the structure character of molecular chain and performance of PMIA have been introduced. Additionally, the common used polymerization techniques for PMIA have been described in detail. These synthesis techniques include low-temperature solution polymerization, interfacial polymerization and emulsion polymerization.

Abstract: In this paper, the photodegradation mechanism of PMIA under ultraviolet light is described in detail. Due to the presence of amide groups, the molecular chains are easily to be broken by exposure to ultra-violet light, which leads to the significant drop of the PMIA’s mechanical performance and meanwhile the fiber’s color becomes dark. To improve the UV resistance performance of PMIA, two methods have been discussed. The first method is melt-mixing, by adding UV absorbers to PMIA, such as benzophenone, triazine, benzotriazole and hindered anime etc. These UV absorbers consume the ultraviolet light’s energy and protect polymeric and other light-sensitive materials from degradation by sunlight or UV. The second method is adding monomers with ultraviolet resistance during the polymerization. This is a promising solution allowing better structure stability of PMIA.