Electrospinning and Structure of Bicomponent Polycaprolactone/Gelatin Nanofibers Obtained Using Alternative Solvent System

Bicomponent polycaprolactone/gelatin (PCL/Gt) nanofibers were successfully formed for the first time by electrospinning using a novel polymer–solvent system with solvents being alternative to the commonly used toxic solvents like fluorinated alcohols. The mixture of acetic acid (AA) with formic acid (FA; 90:10) was applied. Stable electrospinning was possible despite the fact the mixture of PCL and gelatin in AA/FA solvent showed emulsive structure. From the practical perspective, there is no doubt that it is possible to obtain PCL/Gt fibers using AA/FA mixture with morphology similar to that for fibers spun from hexafluoroisopropanol (HFIP) solutions.     

氮化镓纳米纤维的静电纺制备及光催化性能研究

以聚乙烯吡咯烷酮(PVP)和Ga(NO3)3为前驱体,利用静电纺丝和热处理技术制备了直径在100～300 nm左右的单斜结构的Ga2O3纳米纤维,并通过氨气氮化技术制备了GaN纳米纤维。XRD结果表明GaN样品为六方纤锌矿结构,且最佳氮化温度为850℃,氮化时间为2 h。Raman光谱发生了红移,并再次确定了GaN样品的结构,TGA结果表明GaN纤维在700℃以下在空气和氮气气氛下具有较好的稳定性,SEM和TEM表明纤维直径大约在100～200 nm之间,光催化测试表明GaN纤维对罗丹明6G有很好的降解效果。     

静电纺再生丝素纳米纤维的结构与性能

静电纺丝获得的丝素纳米级纤维可作为细胞培养支架,用于纺丝工艺及后处理能改变丝素微细结构,影响其水溶性和力学性能。本文采用XRD、FTIR、固态13CNMR和DSC研究了不同工艺下丝素纳米纤维及经甲醇处理后的微细结构,比较了不同微细结构下的水溶性和力学性能。结果表明,电纺丝的微细结构受纺丝工艺影响,高电压、纺丝液中丝素质量分数大时纺得的电纺丝结晶度高,经甲醇处理后,β化程度提高;w(丝素)=11%、15%时制备的电纺丝断裂强度分别为8.5、11.9 cN/mm;w(丝素)=11%、19%,水溶性由51.2%下降到43.3%;w(丝素)=19%、电压32 kV制得的电纺丝甲醇处理前后水溶性从43.3%下降到6.6%,说明丝素纳米纤维结晶度提高,强度增加、水溶性下降,满足了细胞支架的要求。     

高分子纳米纤维表面压痕及其分形特征研究

采用静电纺丝法制备了纳米级高分子聚己酸内酯(PCL)纤维,通过扫描电子显微镜和原子力显微镜观察了聚己酸内酯纳米纤维的表面结构和微观特征,并通过原子力显微镜对纤维表面进行纳米压痕实验。实验发现随着压痕深度的变小,纤维的弹性模量呈现增大的趋势。利用统计分形理论对高分子纤维表面压痕过程进行建模,通过拟合实验曲线得到了材料的分形参数,该模型可以很好的模拟高分子纤维材料在纳米压痕实验中的尺寸效应。     

聚合物接枝纳米碳纤维/聚苯乙烯复合材料的制备与力学性能研究

采用自由基聚合方法,在纳米碳纤维(CNF)表面接枝聚丙烯酸正丁酯(PnBA)和聚苯乙烯(PS),利用接枝的嵌段聚合物作为大分子偶联剂制备CNF/PS复合材料。红外傅里叶变换光谱(FT-IR)研究表明,嵌段聚合物PnBA-b-PS被成功地接枝到CNF表面。扫描电子显微镜(SEM)和力学性能测试结果显示,CNF与PS复合材料界面结合得到改善,力学性能明显提高。     

聚己内酯静电纺丝纳米纤维与环氧树脂复合涂层防腐性能的研究

利用静电纺丝法在Q345钢表面制备聚己内酯(PCL)与缓蚀剂二巯基苯并噻唑(MBT)的纳米纤维膜PCL/MBT,然后在其表面旋涂环氧树脂(EP),得到复合涂层。通过电化学阻抗谱技术研究了复合涂层的防腐蚀性能。结果表明:在温度为25 ℃、湿度20%、纺丝电压15 kV、接收距离18 cm、V(氯仿)∶V(丙酮)=2∶3的条件下,PCL质量分数为12%,MBT质量浓度为0.01 g/mL时,静电纺丝得到的纳米纤维表面光滑,粗细均匀。电化学测试结果表明:EP/PCL/MBT复合涂层的防腐性能优于EP/PCL或EP涂层。     

Preparation and Characterization of Gelatin Nanofibers Containing Silver Nanoparticles

Ag nanoparticles (NPs) were synthesized in formic acid aqueous solutions through chemical reduction. Formic acid was used for a reducing agent of Ag precursor and solvent of gelatin. Silver acetate, silver tetrafluoroborate, silver nitrate, and silver phosphate were used as Ag precursors. Ag⁺ ions were reduced into Ag NPs by formic acid. The formation of Ag NPs was characterized by a UV-Vis spectrophotometer. Ag NPs were quickly generated within a few minutes in silver nitrate (AgNO₃)/formic acid solution. As the water content of formic acid aqueous solution increased, more Ag NPs were generated, at a higher rate and with greater size. When gelatin was added to the AgNO₃/formic acid solution, the Ag NPs were stabilized, resulting in smaller particles. Moreover, gelatin limits further aggregation of Ag NPs, which were effectively dispersed in solution. The amount of Ag NPs formed increased with increasing concentration of AgNO₃ and aging time. Gelatin nanofibers containing Ag NPs were fabricated by electrospinning. The average diameters of gelatin nanofibers were 166.52 ± 32.72 nm, but these decreased with the addition of AgNO₃. The average diameters of the Ag NPs in gelatin nanofibers ranged between 13 and 25 nm, which was confirmed by transmission electron microscopy (TEM).     

静电纺丝法制备碳纳米纤维及其应用

碳纳米纤维由于因其比表面积大、导电和导热性好,被广泛用于催化剂载体、吸附和储能材料。静电纺丝是制备一维纳米纤维直接、有效的方法,在介绍静电纺丝的基本原理和工艺影响因素的基础上,综述了电纺碳纳米纤维的特性及其应用。     

The Influence of Pre‐Electrospinning Plasma Treatment on Physicochemical Characteristics of PLA Nanofibers

Morphology, crystallinity, thermal, and mechanical properties of nanofibrous mats are known to highly affect the behavior of these materials in desired applications. In this study, multiple characteristics of poly(lactic acid) (PLA) nanofibrous mats prepared from plasma‐treated pre‐electrospinning solutions are studied as a function of various plasma operational parameters. X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, X‐ray photoelectron spectroscopy, scanning electron microscopy, and tensile tests are performed. In addition, the pristine and plasma‐treated PLA solutions are examined with size exclusion chromatography to study the effect of the conducted pre‐electrospinning plasma treatments (PEPT) on the molecular weight of PLA. Aging analysis of the pristine and plasma‐treated solutions is also performed by evaluating the viscosity, conductivity, surface tension, and pH during an aging period of 10 days. To investigate if the results are only affected by the plasma treatment or also affected by the electrospinning, pristine and plasma‐treated PLA cast layers are also analyzed. The results reveal that PEPT preserved the surface chemical composition of the nanofibers and the molecular weight distribution of PLA, while morphology and mechanical properties of the nanofibers are considerably enhanced. Moreover, plasma‐treated polymer solutions resulted in the formation of nicely elongated nanofibers up to 4 days after plasma treatment.     

Role of Draw Rate and Molecular Weight when Electrospun Nanofibers are Post-Drawn with Residual Solvent

The postdrawing process is poorly understood for polymer nanofibers due to the difficulty of manipulating nanofiber structures. Here, an angled track system facilitates postdrawing of individual nanofibers with control of parameters including molecular weight, draw rate, draw ratio, and solvent evaporation time. In this study, the effects of molecular weight, draw rate, and relative residual solvent content on final nanofiber properties are investigated. Molecular weight is first investigated to clarify any influence polymer chain length can have on drawing in facilitating or hindering chain extensibility. Polyacrylonitrile nanofibers with 50 and 150 kDa molecular weights behave similarly with postdrawing resulting in reduced diameters and enhanced mechanics. Since solvent quantity during drawing is a time sensitive component it is meaningful to assess the impact of draw rate on the chemical and structural makeup of postdrawn fibers. Chemical bond vibrations and chain orientation are sensitive to draw rate when polycaprolactone nanofibers are dried for 3 minutes prior to postdrawing, but this dependency to draw rate is not observed when fibers are postdrawn immediately upon collection. These findings demonstrate that the amount of retained solvent at collection is relevant to this postprocessing approach, and highlights the dynamics of solvent evaporation during postdrawing.     

Role of rheology on the formation of Nanofibers from pectin and polyethylene oxide blends

Characterizing the parameters critical to the prediction of a successful electrospinning process from solution properties is essential, yet, not easy in the case of biopolymers. In this study, we attempted to present a broad perspective by simultaneously evaluating the effect of eight different parameters, namely zero shear viscosity, tip viscosity, elastic modulus, phase angle, cohesive energy, pH, conductivity, and surface tension, on the formation of smooth pectin nanofibers. Our results showed that (1) the viscosity of the solution is not an indication of jet formation, but once the jet is formed, high zero shear viscosity and high tip viscosity are required to maintain a dominant whipping instability for smooth nanofiber formation and (2) while evaluating the elasticity of the spinning solutions, comparing only the elastic modulus values would be misleading, since low phase angle values are also necessary for pectin solutions to be electrospun into nonbeaded fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48294.     

Piezoelectric and Electrostatic Properties of Electrospun PVDF‐TrFE Nanofibers and their Role in Electromechanical Transduction in Nanogenerators and Strain Sensors

Piezo‐ and ferroelectric nanofibers of the polymer poly(vinylidenefluoride) (PVDF) have been widely employed in strain and pressure sensors as well as nanogenerators for energy harvesting. Despite this interest, the mechanism of electromechanical transduction is under debate and a deeper knowledge about relevant piezoelectric or electrostatic properties of nanofibers is crucial to optimize transduction efficiency. Here poly(vinylidenefluoride‐trifluoroethylene) nanofibers at different electrospinning conditions are prepared. Macroscopic electromechanical response of fiber mats with microscopic analysis of single nanofibers performed by piezoelectric and electrostatic force microscopy are compared. The results show that electrospinning favors the formation of the piezoelectric β‐phase in the polymer and leads directly to piezoelectric properties that are comparable to annealed thin films. However, during electrospinning the electric field is not strong enough to induce direct ferroelectric domain polarization. Instead accumulation of triboelectric surface charges and trapped space charge is observed in the polymer that explain the electret like macroscopic electromechanical response.     

Fabrication and Characterization of Ionic Conducting Nanofibers

The electrospinning method was used to fabricate nanostructures of Nafion‐poly(vinyl alcohol) (PVA) and Nafion‐poly(ethylene oxide) (PEO). Depending on the ratio between the two polymers, nanospheres and/or nanofibers could be obtained in a reproducible manner. The Nafion‐PVA mats were found to be more conductive than the Nafion‐PEO ones, possibly because of their better mechanical properties when swollen by water. The fiber morphology was always found to be more conductive than the sphere morphology. However, all electrospun mats presented ionic conductivities slightly lower than extruded Nafion 115 or Nafion‐PVA cast films.

     

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.     

Structuring and Molding of Electrospun Nanofibers: Effect of Electrical and Topographical Local Properties of Micro‐Patterned Collectors

The controlled deposition of electrospun nanofibers at the micro‐scale is studied. Several collectors with microscopic patterns are prepared using photolithography. Nanofiber deposition is influenced by the geometry, the size, and the distance between micro‐patterns. Within certain conditions, membranes with multiple “micro spider‐webs” or perpendicularly interconnected microgrids are obtained. Dielectric micro‐holes having a conductive bottom can be filled by the nanofiber. This kind of micro‐molding is rationalized using simulations that show the influence of the collector relative permittivity on the electric field at the pattern vicinity. “Micro‐woven” membranes of PCL with good mechanical properties can be produced, allowing their use for biomedical applications in tissue engineering.

     

Improving Mechanical Properties of Carbon/Epoxy Composite by Incorporating Functionalized Electrospun Polyacrylonitrile Nanofibers

Electrospun functionalized polyacrylonitrile grafted glycidyl methacrylate (PAN‐g‐GMA) nanofibers are incorporated between the plies of a conventional carbon fiber/epoxy composite to improve the composite's mechanical performance. Glycidyl methacrylate (GMA) is successfully grafted onto polyacrylonitrile (PAN) polymer powder via a free radical mechanism. Characterization of the electrospun PAN and PAN‐g‐GMA nanofibers indicates that the grafting of GMA does not significantly alter the tensile properties of the PAN nanofibers but results in an increase in the diameter of nanofibers. Statistical analysis of the mechanical characterization studies on PAN‐carbon/epoxy hybrid composites conclusively shows that the composite reinforced with functionalized PAN nanofibers has greater mechanical properties than that of both the neat PAN nanofiber enriched hybrid composite and control composite (without nanofibers). The improved performance is attributed to the grafted glycidyl groups on PAN, leading to stronger interactions between the nanofibers and the epoxy matrix. PAN‐g‐GMA nanofiber reinforced composite outperforms their neat PAN counterparts in tensile strength, short beam shear strength, flexural strength, and Izod impact energy absorption by 8%, 9%, 6%, and 8%, respectively. Compared to the control composite, the improvements resulting from the PAN‐g‐GMA nanofiber incorporation are even more pronounced at 28%, 41%, 32%, and 21% in the corresponding tests, respectively.

     

Synthesis and Substrate-Aided Alignment of Porphyrinated Poly(ethylene oxide) (PEO) Electrospun Nanofibers

Aligned and unaligned vanadium (IV) oxide meso-tetraphenyl porphine (VMP)/polyethylene oxide (PEO) hybrid nanofibers have been successfully synthesized by electrospinning technique. The nanofibers were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), optical microscopy and scanning electron microscopy (SEM). The SEM and AFM analyses of the morphology showed that the nanofibers are cylindrical with diameters ranging from 400–700 nm. The AFM analysis also confirmed that the aligned nanofibers deposited on a small metallic spring are smoother than the unaligned ones deposited on FTO. FTIR analysis showed that the polar environment provided by the phenyl groups of VMP molecules modified the chemical configuration of PEO molecules, and XRD studies indicated that the VMP molecules were homogeneously distributed within the PEO matrix.     

纤维素基碳纳米纤维对ABS性能的影响

纤维素纳米纤维(CNF)水凝胶经过冷冻干燥、炭化制备纤维素基碳纳米纤维(CCNF),并将CCNF用于增强丙烯腈-丁二烯-苯乙烯(ABS)树脂。结果表明:不同浓度CNF炭化产物均以三维网状碳纳米纤维结构为主。氢、氧元素的脱除反应主要发生在低于400℃时,在1 000℃时芳环中的C=C峰几乎消失。ABS/CCNF复合材料拉伸强度随着CCNF含量的增加先增加而后下降,质量分数1%时达到最大值,拉伸强度为43 MPa,模量随着CCNF含量的增加而升高。     

Highly‐Aligned Electrospun Luminescent Nanofibers Prepared from Polyfluorene/PMMA Blends: Fabrication,Morphology, Photophysical Properties and Sensory Applications

Highly‐aligned luminescent electrospun nanofibers were successfully prepared from two binary blends of PFO/PMMA and PF⁺/PMMA. The PFO/PMMA aligned electrospun fibers showed a core/shell structure but the PF⁺/PMMA fibers exhibited periodic aggregate domains in the fibers. The aligned fibers had polarized steady‐state luminescence with a polarized ratio as high as 4, much higher than the non‐woven electrospun fibers or spin‐coated film. Besides, the PF⁺/PMMA aligned electrospun fibers showed an enhanced sensitivity to plasmid DNA. Such aligned electrospun fibers could have potential applications in optoelectronic or sensory devices.

     

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。