Key Engineering Materials Vols. 645-646

Abstract: In this paper composite nanofiber membranes were prepared by electrospinning technology from poly (vinylidene fluoride) (PVDF)-poly (methyl methacrylate) (PMMA)-SiO₂ blend solutions with different PMMA and SiO₂ contents. It was found that the diameter of electrospun nanofibers was greatly increased with the added PMMA content but decreased with the added SiO₂ content, and when both PMMA and SiO₂ were added the diameter of electrospun nanofibers was decreased. With a proper ratio of the PMMA and SiO₂ added, the electrospum nanofiber membrane could have a suitable diameter with high porosity. The XRD results revealed that electrospun nanofiber membranes contained mainly β-phase crystal structure of PVDF, and its crystalline is reduced with the added PMMA and SiO₂ contents due to the inhibited crystallization of the polymer by the inorganic particles and PMMA during the solidification process. These nanofiber membranes exhibited a high electrolyte uptake, around 300%. Moreover, the incorporation of PMMA and SiO₂ into the nanofiber membrane improved the ionic conductivity from 1.7×10⁻³S/cm to 2.0×10⁻³S/cm at room temperature. Compared with commercial film PE, their cell cycle and charge and discharge performance were also greatly improved.

Abstract: A promising anode material for lithium ion batteries is reported in this paper. It is one-dimensional SnO₂−graphene composite nanofibers (SnO₂−G nanofibers) fabricated by using electrospinning technique. In the study, X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to characterize its structural and morphological properties. Samples with different ratio of SnO₂ to graphene (wt%) are prepared to investigate its electrochemical performance. Galvanostatic charge/discharge tests reveals that Li-insertion/extraction is carried out through a two-phase reaction mechanism that is supported by galvanostatic charge−discharge profiles. It is found that the optimal proportion of SnO₂ to graphene is 8:1 (wt%) for the electrospun composite materials. Furthermore, micro thin film batteries have been fabricated and tested. The results show that initial discharge capacity is 301.86 mA h g⁻¹ at current density of 50 μA g⁻¹, and battery can retain 63.3% of reversible capacity after 300 cycles, which is 5 times higher than bare SnO₂.

Abstract: In the design of the micro electromagnetic vibration harvester, an important goal is maximization of the magnetic flux linkage gradient, which directly determines the induced voltage and output power of the electromagnetic vibration harvester. This paper established a numerical model based on structure of the electromagnetic vibration energy harvester. An analytic expression for the magnetic field of rectangular permanent magnets is used to build up an electromagnetic coupling model. The magnetic field distribution of the rectangular permanent magnet was analyzed. The effects of the gap between the magnet and the coil on the load voltage of the electromagnetic vibration energy harvester were investigated. According to the formula, the magnetic flux linkage and flux gradient were calculated to optimize the geometrical parameter of the magnet and coil. The method and boundary conditions of optimizing the gap between the magnet and coil were presented. The maximum output voltage can be obtained by optimizing the gap between the magnet and the coil. A simple prototype was fabricated and measured to validate the theoretical deducing and the feasibility of method.

Abstract: This paper presents two electromagnetic vibration energy harvesters based on micro-electro-mechanical (MEMS) technology. Two prototypes with different vibration structures were designed and fabricated. The energy harvester includes a permanent magnet attached on vibration structure (resonator) made by Si and a fixed wire-wound coil, with the total volume of 0.9 cm³. Two energy harvesters with different resonator are tested and compared. Experiments show that: in the same acceleration and a load resistance, the resonant frequency of prototype B is approximately 95% of prototype A; The peak-peak voltage and the maximum power of prototype B is 1.6 times and 2.7 times of prototype A respectively. The test results was analyzed simply and it indicated that the electromagnetic energy harvesting with the spring B has better performance; also proved that the potential ability of the non-linear spring could extend the frequency bandwidth and improve output voltage.

Abstract: In order to improve the anti-corrosion characteristic of Ag-coated 316SS bipolar plates in PEMFC environment, self-assembled monolayer (SAM) was prepared on its surface by chemical methods. The electrochemical characteristic of modified bipolar plate was also investigated. The results indicated that the SAM was composed of dodecyl thioalcohol. After forming SAM, the bipolar plate’s contact angle increased from 58° to 102°. In addition, its double layer capacitance (Cd) was decreased and charge transfer resistance was increased. The homogeneous SAM, which acted as a protective barrier, inhibited the corrosive ion from corroding. SAM may provide significant protection against corrosion in PEMFC environment.

Abstract: In order to develop safe and sustainable food and pharmaceutical emulsions, bacterial cellulose (BC) nanofibrils were prepared to stabilize maize oil/water Pickering emulsions. The influence of BC content and pH value on the emulsion stability was explored. Droplet diameters decreased with BC contents in emulsions. At pH 12, the emulsions were most stable among all tested pH values. The transformation of emulsion structure from liquid to gel-like at 8-15°C with BC content higher than 1.55 g/L is predominantly depended on the viscoelastic entangled BC network. These results can have meaningful inspiration of designing edible food and pharmaceutical emulsions.

Abstract: At present, the majority dielectrophoresis chip designs optimize their performance by electric simulation and fluid field simulation. The lack of further cells force analysis and movement prediction results in a limited cell dielectrophoresis enrichment efficiency. The HepG2 hepatoma carcinoma cell movement under the action of dielectrophoresis force, fluid force and gravity was analyzed respectively by Comsol Multiphysics software. The preliminary optimization conditions for the cell enrichment were obtained. According to the simulation results, the experiments were carried out to investigate the enrichment effect of the HepG2 hepatoma carcinoma cells. The experiment result demonstrated the enrichment efficiency of HepG2 hepatoma carcinoma cells was reached to 88.89% under the 5 V amplitude and 4 MHz frequency sinusoidal signal excitation.

Abstract: Functionalized SBA-15 with mesoscopic pore channels was synthesized by co-condensation of tetraethoxysilane and (3-aminopropyl) triethoxysilane (APTES) via hydrothermal process. Small-angle X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy were used to monitor the effect of surface functionalization on the structural and textural features of the SBA-15. The results suggested that the structural ordering of functionalized SBA-15, as well as pore diameters, pore volumes and surface areas, were decreased with increasing the APTES molar ratio. Candida rugosa lipase (CRL) was used as a model enzyme for studying the effect of amino-functionalized on loading amount and enzymatic activity. The effects of pH and temperature on catalytic hydrolysis of tributyrin by immobilized CRL were investigated. The results showed that immobilized CRL had a well adaptability in a wide pH and temperature region, and CRL immobilized on functionalized SBA-15 exhibited much higher enzymatic activity than free CRL, especially, 5 mol% APTES functionalized SBA-15 immobilized CRL displayed the highest activity.

Abstract: This paper presents a pendulous resonant MEMS biosensor for liquid detection based on SOI-MEMS technology. The biosensor consists of two electromagnetically driven and sensed resonant paddles working in the torsional mode. The differential output consisted by the two paddles provides the sensor reading. 1um thick SiNx is deposited on the electrodes by plasma enhanced chemical vapor deposition (PECVD), making the biosensor capable of working in liquid directly. In device fabrication, SOI-MEMS fabrication processes were utilized, where a new modified buffered hydrofluoric acid (BHF) solution was used to remove the buried oxide layer and release the paddles. High-current drive circuit and energy compensation circuit are designed to improve the Q-factor of the paddle in liquid. Experimental experiments show that the biosensor can distinguish the density of some liquid effectively．

Abstract: Hollow silica microspheres with porous surface were synthesized by using the pollen grains as biotemplate through an in-situ synthesis process, in which the pollen grains were surface modified by ammonium oleate. Scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption-desorption porosimetry analyzer were applied to investigate the as-prepared microspheres. Bovine serum albumin was used as the model drug to estimate the adsorption property. And the effect of the different amount of tetraethoxysilane during the synthesis process were discussed in this paper. Results indicated that the hierarchical network of the pollen wall could be well replicated through this method, in which the hydrophobic interaction between the pollen wall and surfactant as well as the electrostatic interaction between the surfactant and the hydrolysate of tetraethoxysilane were considered as the key factors for the replication. The hollow silica microspheres have loading capacity for the model drug, and the adsorption property of this microsphere could be easily adjusted by changing the amount of tetraethoxysilane.