Emission Based Sensing of Subnanomolar Dissolved Carbon Dioxide Exploiting Electrospun Nanofibers

In this work, the authors report a novel emission-based optical sensor for dissolved carbon dioxide. Ethyl cellulose has been used together with an imidazolium based ionic liquid as matrix material. Sensors were fabricated either in form of continuous thin films or nanofibers. The offered composition exhibited enhanced stability and excellent detection limits for sensing of bicarbonate. The preliminary analysis of calibration plots show that the sensitivity of electrospun nanofibrous membranes to detect bicarbonate is at least 5-fold better than that of the thin films. The stability of the indicator in the employed matrix was superior to the previously reported ones.     

金属催化剂对碳纳米纤维结构影响的研究进展

综述了不同种类的金属催化剂及同种催化剂不同状态对碳纳米纤维的结构和形貌的影响,并对今后自组装生产各种结构形态的碳纳米纤维进行了展望。     

Fabrication and Thermal Dissipation Properties of Carbon Nanofibers Derived from Electrospun Poly(Amic Acid) Carboxylate Salt Nanofibers

Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI‐based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp² bonding between carbon atoms.     

Synthesis of Organosilane‐Modified Carbon Nanofibers and Influence of Silane Coating Thickness on the Performance of Polyethylene Nanocomposites

Silane coatings with different thicknesses were synthesized on CNFs for reinforcement of polyethylene composites. The thickness of the silane coating was adjusted by using a basic catalyst to increase the overall reactivity of the silane groups, resulting in a thick coating of ≈46 nm (ca. 90% increase in fiber diameter). DMA performed on the polyethylene composites showed a substantial increase in storage modulus from 1.68 to 2.34 GPa (40%) at low temperatures in the composite with the thick silane coating (≈46 nm) at a low loading of 0.4 wt.‐%. We believe that the silane‐treated nanofillers with thick coatings are very promising for high‐performance nanocomposites with non‐polar polymer matrices.

     

Production of Trans-Cinnamic Acid by Immobilization of the Bambusa oldhamii BoPAL1 and BoPAL2 Phenylalanine Ammonia-Lyases on Electrospun Nanofibers

Phenylalanine ammonia-lyase (PAL) catalyzes the nonoxidative deamination of phenylalanine to yield trans-cinnamic acid and ammonia. Recombinant Bambusa oldhamii BoPAL1/2 proteins were immobilized onto electrospun nanofibers by dextran polyaldehyde as a cross-linking agent. A central composite design (CCD)-response surface methodology (RSM) was utilized to optimize the electrospinning parameters. Escherichia coli expressed eBoPAL2 exhibited the highest catalytic efficiency among four enzymes. The optimum conditions for fabricating nanofibers were determined as follows: flow rate of 0.10 mL/h, voltage of 13.8 kV, and distance of 13 cm. The response surface models were used to obtain the smaller the fiber diameters as well as the highest PAL activity in the enzyme immobilization. Compared with free BoPALs, immobilized BoPALs can be reused for at least 6 consecutive cycles. The remained activity of the immobilized BoPAL proteins after storage at 4 °C for 30 days were between 75 and 83%. In addition, the tolerance against denaturants of the immobilized BoPAL proteins were significantly enhanced. As a result, the dextran polyaldehyde natural cross-linking agent can effectively replace traditional chemical cross-linking agents for the immobilization of the BoPAL enzymes. The PAL/nylon 6/polyvinyl alcohol (PVA)/chitosan (CS) nanofibers made are extremely stable and are practical for industrial applications in the future.     

Effect of Processing Variables on the Morphology of Electrospun Poly[(lactic acid)‐co‐(glycolic acid)] Nanofibers

A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.

     

Covalent Immobilization of Tyrosinase on Electrospun Polyacrylonitrile/Polyurethane/Poly(m-anthranilic acid) Nanofibers: An Electrochemical Impedance Study

Polyacrylonitrile/polyurethane/poly(m-anthranilic acid) nanofibers were fabricated by electrospinning. Tyrosinase immobilization was performed by EDC/N-hydroxyl succinimide activation. Covalent binding of tyrosinase onto nanofibers was confirmed by Fourier transform infrared-attenuated total reflectance, and bicinchoninic acid assay revealed the amount of enzyme. Nanofiber morphology and composition were characterized by scanning electron microscopy/energy-dispersive X-ray spectroscopy (EDX). Nanofibers became smoother and thicker after tyrosinase immobilization. Effects of enzyme on nanofibers were investigated by electrochemical impedance spectroscopy and the data were fitted to equivalent electrical circuit model. EDX-mapping showed uniform distribution of enzyme. The solution resistance and charge transfer resistance of nanofibers decreased after enzyme immobilization.     

纤维热处理对C/C-SiC复合材料剪切强度的影响

对T300碳纤维在真空环境下,在600、900、1200、1500℃进行热处理,用液硅熔渗反应法(liquid silicon infiltration,LSI)制备了不同微观组织结构的C/C-SiC复合材料。采用光电子能谱分析了热处理对纤维表面结构的影响,用光学显微镜和扫描电子显微镜对材料微观形貌进行了观察分析。采用双槽口剪切法(DNS)测试了C/C-SiC复合材料层间剪切强度(interlaminar shear strengh,ILSS),并分析了纤维热处理对材料剪切性能影响的微观机理。结果表明：碳纤维经热处理后,表面化学成分发生变化,氧含量显著降低,改变了碳纤维增强树脂基复合材料(carbon fiber reinforced resin matrix composite,CFRP)先驱体中纤维/树脂界面结合强度,从而在CFRP裂解后形成了具有不同微观结构的C/C预制体,通过液Si对不同微结构的C/C预制体进行熔渗,获得具有不同微观结构的 C/C-SiC复合材料;DNS 测试发现碳纤维热处理能够有效改善 C/C-SiC复合材料的层间剪切强度,主要是由于纤维经热处理后制备的C/C-SiC复合材料中,SiC基体相分布较均匀并包裹在碳纤维周围,导致纤维/基体界面结合强度高。经1500℃热处理纤维增强的C/C-SiC复合材料,其剪切强度为34 MPa,与未处理的相比,ILSS提高了33%。     

热处理对聚乙烯醇薄膜性能的影响

通过改变热处理温度和处理时间研究了热处理条件对聚乙烯醇薄膜性能的影响。结果表明，聚乙烯醇吹塑薄膜经热处理后结晶度增大。薄膜在130℃下热处理300s后，室温下水溶时间由未处理的1297s延长至2841s，增加119．04％；失重率增大4．6％；拉伸强度由未处理的23．86MPa增大至73．25MPa，提高207．00％，同时，断裂伸长率由未热处理的255％下降到100％，下降了60．78％；透光率由未处理的91．9％下降到88．5％。下降了3．70％。     

Modifications of carbon for polymer composites and nanocomposites

The various forms of carbon used in composite preparation include mainly carbon-black, carbon nanotubes and nanofibers, graphite and fullerenes. This review presents a detailed literature survey on the various modifications of the carbon nanostructures for nanocomposite preparation focusing upon the works published in the last decade. The modifications of each form of carbon are considered, with a compilation of structure-property relationships of carbon-based polymer nanocomposites. Modifications in both bulk and surface modifications have been reviewed, with comparison of their mechanical, thermal, electrical and barrier properties. A synopsis of the applications of these advanced materials is presented, pointing out gaps to motivate potential research in this field.