Electrospinning of collagen-chitosan complex

The collagen-chitosan complex nanofibers have been prepared for the first time by electrospinning. The mixed HFP/TFA (the volume ratio of 90/10) was found to be the appropriate solvent for electrospinning. The concentration of the spinning solution and the ratio of chitosan/collagen were varied and adjusted to get smooth nanofibers. It was found that the diameter of the spun fibers became thick with the concentration of the solution increasing and became fine with the ratio of the chitosan/collagen increasing. We have characterised the molecular interactions in collagen-chitosan complex by Fourier transform infrared spectroscopy. The spun fibers are designed to mimic the native extracellular matrix for tissue engineering and to develop functional biomaterials.     

静电纺丝制备PVDF多孔纳米纤维及其在吸油中的应用

采用静电纺丝和PEO模板相结合加工制备了具有超疏水性能的PVDF多孔纳米纤维.通过扫描电镜(SEM)观察所制备的PVDF纤维具有均匀微纳米二级孔道显微结构,测得该多孔纳米纤维表面接触角高达158°,呈现良好的超疏水特性.研究发现,将PVDF多孔纳米纤维作为溢油吸附材料具有良好的吸油效能,其对润滑油、柴油、植物油和汽油的...     

Jet Shaping Nanofibers and the Collection of Nanofiber Mats in Electrospinning

Electrospinning is an effective way to produce nanofibers. The concentration or the corresponding viscosity of the spin solution is one of the most important variables to control the fiber morphology in electrospinning. Jet shaping nanofibers might be divided in two operating modes for different solution viscosity： split thinning and single thinning. From the analysis of jet single thinning, an equation to calculate the velocity of nanofibers depositing on the collector was educed and it was found that the velocity range was very different from the reported result. For the electrospun mats obtained from low solution concentration, the split is observed by scanning electron microscopy （SEM） images. On the other hand, the beads formation in the nanofiber mats can be explained well by jet splitting. The arrangement of nanofibers in the mats is related to the methods of collection, and the cylinder collector gets more ordered mats. This result is proved by so-called break strengths testing and SEM images of the mats obtained from different methods of collection.     

Transient charge-masking effect of applied voltage on electrospinning of pure chitosan nanofibers from aqueous solutions

Abstract

The processing of a polyelectrolyte (whose functionality is derived from its ionized functional groups) into a nanofiber may improve its functionality and yield multiple functionalities. However, the electrospinning of nanofibers from polyelectrolytes is imperfect because polyelectrolytes differ considerably from neutral polymers in their rheological properties. In our study, we attempt to solve this problem by applying a voltage of opposite polarity to charges on a polyelectrolyte. The application of this ‘countervoltage’ can temporarily mask or screen a specific rheological property of the polyelectrolyte, making it behave as a neutral polymer. This approach can significantly contribute to the development of new functional nanofiber materials.     

Transient charge-masking effect of applied voltage on electrospinning of pure chitosan nanofibers from aqueous solutions

The processing of a polyelectrolyte (whose functionality is derived from its ionized functional groups) into a nanofiber may improve its functionality and yield multiple functionalities. However, the electrospinning of nanofibers from polyelectrolytes is imperfect because polyelectrolytes differ considerably from neutral polymers in their rheological properties. In our study, we attempt to solve this problem by applying a voltage of opposite polarity to charges on a polyelectrolyte. The application of this ‘countervoltage’ can temporarily mask or screen a specific rheological property of the polyelectrolyte, making it behave as a neutral polymer. This approach can significantly contribute to the development of new functional nanofiber materials.     

Atomic force microscopy visualization of hard segment alignment in stretched polyurethane nanofibers prepared by electrospinning

Molecular-level orientation within nanofibers has been attracting attention as a tool for controlling and designing highly functional nanofibers. In this study, we used atomic force microscopy to visualize the phase separation between soft and hard segments on a polyurethane (PU) nanofiber surface prepared by electrospinning. Furthermore, the stretched nanofibers prepared with a high-speed rotating collector were found to have a different phase distribution in the phase-separated structure, with the hard segment domains aligned to the fiber axis. In contrast, unstretched PU nanofibers prepared without rotation were observed to have nonuniformly distributed segments. These results indicate that the application of an intense elongation force along the nanofiber axis with a rotating mandrel collector changed the distribution of segment alignments.     

Stability of Non-axisymmetric Electrolyte Jet in High-frequency AC Electric Field

In the present work linear instability of capillary non-axisymmetric micro-jets of electrolyte solutions in a high-frequency alternating axial electric field is investigated theoretically. The gravity affects are neglected. The problem is described by strongly coupled nonlinear system of PDEs for ion transport, electrical field and fluid flow. Viscous liquid is taken. The problem can be divided into outer and inner ones. Solution for the unsteady double ion layer is obtained in Debye-Huckel approximation provided that the oscillation frequency is sufficiently high while Pecklet number based on the Debye layer thickness is sufficiently small. The unsteady double ion layer produces additional normal and tangential stresses on the liquid–gas interface; the latter can either stabilize or destabilize the flow. It is shown that only axisymmetric mode is unstable while non-axisymmetric perturbations are always stable. It is also shown that in unstable case there is an essential dependence of the main stability characteristics on the parameter proportional to the frequency of external field. There are two threshold values of the parameter at which a bifurcation of stability parameters occurs. In particular, the size of the formed drops suffers a jump at increase of amplitude of fluctuation of an electric field. The problem is solved in a broad region of its parameters. There is a qualitative agreement of the theory developed with the available experimental data.     

磁镜场约束中粒子运动的数值计算

由单粒子轨道理论,从分析磁镜场中荷电粒子的受力情况出发,应用计算机数值求解方法模拟了磁镜场中荷电粒子的运动情况.结果表明:与经典的理论分析结果不同,当荷电粒子的起始位置与磁轴的距离不等于其拉摩尔半径时,荷电粒子在平行磁轴方向和垂直磁轴平面中的速度分量存在着周期性变化,其周期为荷电粒子的拉摩尔周期;同时其损失锥的临界角随着荷电粒子起始位置与磁轴的距离的增大而略有减小.     

大气层不同高度气压对等离子体射流激励器性能影响的研究

为将等离子体射流应用于大气层中的飞行器进行流动控制,对火花放电等离子体合成射流激励器,搭建了一套模拟不同大气层高度气压的真空实验系统,通过改变实验容器内的气压来模拟不同的大气层高度,利用动态压力传感器测量激励器射流出口的压力变化,得到激励器出口射流速度。分别对两个不同结构参数的两电极火花放电等离子体射流激励器进行了实验研究。实验结果表明,随着大气层高度的增加,火花放电等离子体合成射流的峰值速度不减反增;在0~10000m高度之间,射流峰值速度随高度大致成线性关系变化;大气层高度每增加1000 m,射流峰值速度增大15%~25%;在10000 m高度左右,高空射流峰值速度大约是地面的两倍。研究表明,在不同的大气层高度下,加载电压幅值、频率、占空比对激励器性能的作用规律与在地面常压下的作用规律相似。     

Stability analysis of ITER Poloidal Field Coils conductors

The stability analysis [1] of the Poloidal Field Coils of the ITER Project, specially the PF5, PF3 and PF2 coils for scenario #2, normal mode has been performed using the Gandalf [2] code. The conductor stability is assessed in the most severe operating conditions, at the minimal temperature margin time of the 4th pulse. It consists in determining the maximal deposited energy (perturbation in mJ/cm³ of superconducting strands) which can be absorbed without runaway. This study is performed for three initial different designs: Cu–nonCu ratio of 2.3, 1.6 and 4.4 for PF5, and Cu–nonCu ratio of 2.3, 1.6 and 6.9 for PF3 and PF2. The results are presented as well as a discussion about the phenomena, important parameters and uncertainties. For each type of perturbation, the calculated stability limits are quite similar from one design to another. The low Cu–nonCu ratios do not show significant stability degradation compared to the original ITER design with high ratios.     

Effect of Additives on Stability of Etoposide in PLGA Microspheres

The purpose of this article was to determine the shelf life of etoposide in poly(lacticco-glycolic acid) (PLGA) microspheres prepared with and without additives (i.e., tricaprin and isopropyl myristic acid ester [IPM]). The microspheres were prepared by a single-emulsion solvent extraction technique with and without 25% w/w additive. The batches of microspheres were subjected to an accelerated stability study at two elevated temperatures (70°C and 80°C or 80°C and 90°C). Samples were taken at 7, 14, 21, 28, and 35 days for estimation of drug content by high-performance liquid chromatography (HPLC). The drug stability in the microspheres was determined by plotting the log percentage drug remaining versus time to obtain the degradation rate constant k of etoposide at the measured temperature. This degradation rate constant was then used in the Arrhenius equation to obtain the activation energy of etoposide, which was utilized to determine the shelf life of the microspheres at room temperature. The results showed that all three microsphere formulations had good long-term stability at room temperature (6.62-8.86 years at 25°C). The plain microspheres were shown to possess a shelf life of 6.62 years, and the IPM and tricaprin were the most stable with shelf lives of 8.25 and 8.86 years, respectively.     

Effect of Additives on Stability of Etoposide in PLGA Microspheres

The purpose of this article was to determine the shelf life of etoposide in poly(lacticco-glycolic acid) (PLGA) microspheres prepared with and without additives (i.e., tricaprin and isopropyl myristic acid ester [IPM]). The microspheres were prepared by a single-emulsion solvent extraction technique with and without 25% w/w additive. The batches of microspheres were subjected to an accelerated stability study at two elevated temperatures (70°C and 80°C or 80°C and 90°C). Samples were taken at 7, 14, 21, 28, and 35 days for estimation of drug content by high-performance liquid chromatography (HPLC). The drug stability in the microspheres was determined by plotting the log percentage drug remaining versus time to obtain the degradation rate constant k of etoposide at the measured temperature. This degradation rate constant was then used in the Arrhenius equation to obtain the activation energy of etoposide, which was utilized to determine the shelf life of the microspheres at room temperature. The results showed that all three microsphere formulations had good long-term stability at room temperature (6.62-8.86 years at 25°C). The plain microspheres were shown to possess a shelf life of 6.62 years, and the IPM and tricaprin were the most stable with shelf lives of 8.25 and 8.86 years, respectively.     

Fabrication and Magnetic Property of One-dimensional SrTiO3/SrFe12O19 Composite Nanofibers by Electrospinning

The composite nanofibers of SrTiO3/SrFe12O19 with a molar ratio of 1:1 and diameter about 120 nm were prepared by electrospinning. Effects of calcination temperature on the formation, crystallite size, morphology and magnetic property were studied by infrared spectroscopy, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The binary phase of strontium ferrite and titanate was formed after being calcined at 900℃ for 2 h and the composite nanofibers were fabricated from nanograins of SrTiO3 about 24 nm and SrFe12O19 around 33 nm. The crystallite sizes for the nanofibers increase with increasing calcination temperature and the addition of SrTiO3 has an obvious suppression effect on SrFe12O19 grain growth. The specific saturation magnetization and remanence tend to increase with the crystallite size. With increasing calcination temperature from 900 to 1050℃, the coercivity increases initially, achieving a maximum value of 520.2 kA·m-1 at 950℃, and then shows a reduction tendency.     

Effect of a Rotating Magnetic Field on Convection Stability and Crystal Growth in Zero Gravity and on the Ground

A numerical study of the flows arising in a conducting liquid under the action of a rotating magnetic field as well as under its interaction with gravitational and thermocapillary convection has been made. The boundaries of the transition to the oscillating regime of convective flows have been determined. Regions of mixed flows, in which the impurity macrosegregation in crystals grown by the Bridgman and floating-zone methods decrease, have been revealed. It has been shown that regions of flows in which both a smooth increase in the impurity macrosegregation and a change in the form of a clearly defined extremum are observed also exist. The possibilities of mathematical modeling of geophysical problems with the use of a rotating magnetic field are discussed.     

磁浮列车磁场测量系统中运动控制平台的设计

磁浮列车气隙磁场的测量可以为列车电磁系统的设计和控制提供重要依据．本文对气隙测量系统中磁传感器运动控制平台的设计进行了详细介绍,阐述了运动控制平台的工作原理和光栅尺信号的处理方法．采用双计数器鉴相法消除了光栅尺抖动的影响,提高了传感器的定位精度．同时采用电流矢量恒幅旋转的细分方法实现了步进电机恒转矩均匀细分控制,提高了步进电机的分辨率和运行稳定性．所设计的运动控制平台的定位精度可以达到1μm．     

Tailoring of Porous Structure in Macro-Meso-Microporous SiC Ultrathin Fibers via Electrospinning Combined with Polymer-Derived Ceramics Route

Porous SiC has attracted extensive attention for its wide applications, especially in harsh environment, due to its unique properties. In the present paper, novel macro-meso-microporous SiC ultrathin fibers (MMM-SFs) were synthesized through electrospinning process associated with polymer-derived ceramics route, and the porous structure in the SFs can be conveniently tailored by tuning the composition of the spinning solvents and the concentration of the precursor (polycarbosilane). The surface features and microstructures of the resultant MMM-SFs were characterized in detail. These fibers presented a high specific surface area of 86.1–128.2 m² g^?1. The formation mechanism of hierarchically porous structure was discussed as well. N,N′-dimethylformamide (DMF) played a critical role in forming macropores, while the decomposition of SiO_xC_y phase was responsible for the meso-/micropores. Our method utilized to synthesize hierarchically porous SFs is easily capable of designing other ceramic fibers.     

磁场作用对等规聚丙烯结晶行为的影响

通过偏光显微镜(POM)、广角X射线衍射(WAXD)、差示扫描量热仪(DSC)等手段研究了磁场作用对熔融聚丙烯的结晶形态及其与热历史的关系。结果表明,在磁场作用下,聚丙烯球晶尺寸变大,能观察到球晶内部的叶脉状晶体单元;随着熔融温度升高和熔融时间的延长,磁场作用的效果更加明显。磁场作用不利于β晶的生长,会使聚丙烯的结晶更加完善;在磁场作用下熔融、结晶的聚丙烯,结晶度无明显的改变,而于磁场外熔融的聚丙烯在磁场作用下等温结晶时,结晶度有明显的提高。     

Effect of Processing Route on the Stability of Aqueous ZrO2 suspensions

The relationship between processing route and suspension stability in ZrO2-H2O-PANH4 system was investigated through rheology study. The work showed that two suspensions with identical PAN H4 concentration and final solution condition but prepared by different routes differed greatly in stability. This behavior is attributed to their different distribution state of PANH4 on ZrO2 surface that is determined by the adsorption affinity depending on pH condition in solution. High affinity at pH 5.0 induces a nonuniform distribution of soluble PAA- （polyacrylicacid） on particle surface, which can flocculate the suspension strongly, while low affinity at pH 9.0 induces an uniform distribution of polymer so that the higher stabilization can be achieved. A simple mathematical model was used to account for the observed results.