Electrospinning of polyacrylonitrile fibers from ionic liquid solution

We developed a temperature-controlled electrospinning apparatus specially for the polymers/IL system with high viscosity and surface tension and investigated the electrospinning of polyacrylonitrile (PAN)/1-butyl-3-methyl-imidazolium bromide ([BMIM][Br]) solutions. The rheological behaviors, surface tensions and conductivities of PAN/[BMIM]/[Br] solutions at different temperatures indicated that appropriately increasing the temperature is beneficial to their spinnability. It is also shown that PAN/[BMIM]/[Br] with a concentration of 3 wt%, 4 wt% and 5 wt% can be electrospun to fibers by increasing their temperatures to 70°C, 75°C or 85°C, respectively. A rotating drum composed of a dacron mesh was used as a collector in order to avoid the contraction of the wet fibers. This present study provides an alternative method for electrospinning polymer fibers.     

Electrospinning Mechanism for Producing Nanoscale Polymer Fibers

Electrospinning provides a straightforward method to produce polymer fibers with nanoscale diameters. Although the setup for electrospinning is simple and convenient, the spinning mechanism itself is quite complicated. A complete understanding of this mechanism remains to be elucidated and the factors that govern fiber formation are not well understood. In this study, we investigate the electrospinning instabilities by observing the electrospinning jet behaviors with various photographic exposure times ranging from 1/100 to 1/10,000 of a second and the corresponding fiber depositions. We propose an electrospinning mechanism responsible for producing nanoscale fibers and their deposition patterns.     

Effect of Jet Swell and Jet Stretch on the Structure of Wet-Spun Polyacrylonitrile Fiber

The jet swell effect in the wet spinning of polyacrylonitrile (PAN) fiber was studied by optical microscopy and the jet swell ratio was obtained through directly measuring the diameter of the freely extruded fibers. For reflecting the actual drawing situation of the fibers in the coagulation process, the jet stretches were then corrected from the apparent values to the true values, and their effect on the cross-sectional morphology, internal structure, and orientation of the wet-spun PAN fibers was studied by optical microscopy, scanning electron microscopy, and X-ray diffraction, respectively. The results showed that jet stretch plays an important role in eliminating the adverse effects caused by the jet swell effect and affects the fiber structure; PAN fibers of uniform denier, dense and homogenous structure, and high orientation can only be obtained at a suitable jet stretch.     

Poly(m‐Phenylene Isophthalamide) Ultrafine Fibers from an Ionic Liquid Solution by Dry‐Jet‐Wet‐Electrospinning

Ultrafine poly(m‐phenylene isophthalamide) (PMIA) fibers from PMIA solution in an ionic liquid via dry‐jet‐wet electrospinning technology are described. The morphology of the fibers with and without treatment in a coagulation water bath in the dry‐jet‐wet‐electrosinning process was observed by scanning electrical microscopy (SEM) and a high resolution optical microscope. The crystal structure of the fibers was analyzed by wide angle X‐ray diffraction (WAXD). The differences of morphologies and properties between the ultrafine fibers obtained by the electrospinning process and fibers from conventional wet‐spinning technology are discussed. The thermal properties of the ultrafine PMIA fibers were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).     

Novel electrospun PAN�CPVC composite fibrous membranes as polymer electrolytes for polymer lithium-ion batteries

Composite fibrous membranes based on poly(acrylonitrile)(PAN)-poly(vinyl chloride)(PVC) have been prepared by electrospinning. The fibrous membranes are made up of fibers of 850- to 1,300-nm diameters. These fibers are stacked in layers to produce a fully interconnected pore structure. Polymer electrolytes were prepared by immersing the fibrous membranes in 1 M LiClO₄-PC solution for 60 min. The condition of pure PAN polymer electrolytes is jelly, which has poor mechanical performance and cannot be used. But when PVC with a good mechanical stiffener was added to PAN, the condition of composite PAN?CPVC polymer electrolytes becomes free-standing. In addition, the optimum electrochemical properties have been observed for the polymer electrolyte based on PAN?CPVC (8:2, w/w) to show ionic conductivity of 1.05?×?10^?3 S cm^?1 at 25 °C, anodic stability up to 4.9 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. The promising results showed that fibrous PEs based on PAN?CPVC (8:2, w/w) have good mechanical stability and electrochemical properties. This shows a great potential application in polymer lithium-ion batteries.     

Elaboration and characterization of magnetic nanocomposite fibers by electrospinning

We describe a simple method based on the electrospinning process to prepare heterogeneous hybrid submicronic fibers with magnetic behavior, consisting of Co nanoparticles embedded in a polyacrylonitrile (PAN) polymer. Quantity and anisotropy of magnetic nanoparticles are key parameters to improve the specific magnetic properties of fibers. We notably show that for higher Co nanoparticles concentration, their lower dispersity into the resulting fibers lead to dipolar interactions that become demagnetizing. The structural and morphological properties of Co nanodisks and of the resulting nanocomposite fibers are investigated by SEM, TEM, and EDX. The magnetic properties of the hybrid electrospun fibers have been evaluated with a SQUID magnetometer.     

Preparation and Characterization of Polyacrylonitrile and Polyacrylonitrile/β-cyclodextrins Microspheres

Polyacrylonitrile (PAN) and PAN/β-cyclodextrin (β-CD) microspheres were prepared via an electrospinning method. The PAN microspheres could be successfully obtained in a suitable range of concentrations of electrospun PAN solutions. When β-CD was added to the PAN solutions, electrospun PAN/β-CD composite spheres were prepared. The morphology of the spheres was characterized by scanning electron microscopy (SEM); it showed that the spheres had uniform diameter and a smooth surface. The composition of the composite microspheres was studied by Fourier transform infrared spectroscopy (FTIR). The results showed that the β-CD was incorporated in the polymer microspheres.     

Controlled assembly of poly(vinyl pyrrolidone) fibers through an electric-field-assisted electrospinning method

In this paper, we develop an effective electric-field-assisted electrospinning method for the controlled deposition of poly(vinyl pyrrolidone) fibers. The electric field distribution becomes uniform and convergent due to the introduction of a metal plate and a focusing aid into the conventional electrospinning setup. As a result, the bending instability is suppressed and the jet is restricted to moving to the collector along a straight line. Helical structure of fibers with lateral width of about 10 μm is formed and aligned on a rotating substrate. The morphology of helical fibers can also be effectively adjusted by varying the collecting velocity.     

Production of nanofibers by electrospinning under pressurized CO2

Electrospinning is one of the simple technical methods for the production of polymer nanoparticles and nanofibers. Various polymers have been successfully electrospun into ultrafine particles and fibers in recent years mostly in solvent solution and some in melt form. In this work, near- and supercritical CO₂ were used as media for this process. At these conditions, the solubility can be tuned by controlling the temperature and pressure. Therefore, it is possible to form particles and fibers within a thermodynamic window where the biopolymer has been softened, but not dissolved. The experiments were conducted by using electrospinning under pressurized CO₂ system at pressures of ～ 8.0 MPa and temperature of 313 K to produce several polymers fibers. Polyvinylpyrrolidone was used as the starting material. During the electrospinning process, the applied voltage was 10–17 kV and the distance of nozzle and collector was 8 cm. The concentration of polymer solution was 4 wt%. The morphology- and structure-produced fibers were observed by scanning electron microscopy. The results showed that temperature and pressure affected the morphology of fibers produced by electrospinning in pressurized CO₂. This suggests that the thermal behavior of the polymer can be optimized by adjusting the polymer through the adjustment of pressure and temperature by using CO₂ as a solvent.     

Controlling the fiber diameter during electrospinning

We present a simple analytical model for the forces that determine jet diameter during electrospinning as a function of surface tension, flow rate, and electric current in the jet. The model predicts the existence of a terminal jet diameter, beyond which further thinning of the jet due to growth of the whipping instability does not occur. Experimental data for various electrospun fibers attest to the accuracy of the model.     

Electrospun cross linked rosin fibers

In this study, we describe the first reported preparation of rosin in fiber form through use of an electrospinning technique utilizing various solvent systems. The polymer concentration of the formed fiber was studied by using various solvents such as chloroform, ethanol, N-N dimethylformamide (DMF), tetrahydrofuran (THF), acetone, and methylene chloride (MC). An electrospray of the solution resulted in the beaded form of the rosin. By varying the polymer concentration with MC, we were then able to obtain uniform fibers. However, the fibers exhibited large diameter. We believe that it is possible to reduce the diameter of the rosin fibers through appropriate selection of electrospinning parameters. In addition, the morphological transitions from beads, to beaded fiber, to fiber were studied at different polymer concentrations. We propose a possible physical cross linking mechanism for the formation of rosin fibers during the electrospinning process. Our results demonstrate the feasibility of producing fiber nanostructures of rosin by using an electrospinning technique.     

Effect of the Concentration of the Spinning Solution on the Morphology and Properties of Nonwoven Poly-3-Hydroxybutyrate Fibers

The nonwoven fibrous materials of poly-3-hydroxybutyrate obtained by electrospinning were studied. The average diameter of the fibers was correlated with the polymer concentration in solution. As the concentration of poly-3-hydroxybutyrate in the spinning solution increased from 5 to 9 wt %, its crystallinity in the fibrous material increased by 4–5%, and the melting temperature changed insignificantly. A paramagnetic resonance study showed that the density of the amorphous phase of the fibers increased with the polymer concentration in solution. The resistance of the fibrous materials to aggressive environmental factors also increased.     

Electrospinning of Poly(Hydroxybutyrate-co-hydroxyvalerate) Fibrous Scaffolds for Tissue Engineering Applications: Effects of Electrospinning Parameters and Solution Properties

Electrospinning, a technology capable of fabricating ultrafine fibers (microfibers and nanofibers), has been investigated by various research groups for the production of fibrous biopolymer membranes for potential medical applications. In this study, poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), a natural, biocompatible, and biodegradable polymer, was successfully electrospun to form nonwoven fibrous mats. The effects of different electrospinning parameters (solution feeding rate, applied voltage, working distance and needle size) and polymer solution properties (concentration, viscosity and conductivity) on fiber diameter and morphology were systematically studied and causes for these effects are discussed. The formation of beaded fibers was investigated and the mechanism presented. It was shown that by varying electrospinning parameters within the processing window that was determined in this study, the diameter of electrospun PHBV fibers could be adjusted from a few hundred nanometers to a few microns, which are in the desirable range for constructing “biomimicking” fibrous scaffolds for tissue engineering applications.     

Simulation of the 3D viscoelastic free surface flow by a parallel corrected particle scheme

In this work,the behavior of the three-dimensional(3D) jet coiling based on the viscoelastic Oldroyd-B model is investigated by a corrected particle scheme,which is named the smoothed particle hydrodynamics with corrected symmetric kernel gradient and shifting particle technique(SPH_CS_SP) method.The accuracy and stability of SPH_CS_SP method is first tested by solving Poiseuille flow and Taylor-Green flow.Then the capacity for the SPH_CS_SP method to solve the viscoelastic fluid is verified by the polymer flow through a periodic array of cylinders.Moreover,the convergence of the SPH_CS_SP method is also investigated.Finally,the proposed method is further applied to the 3D viscoelastic jet coiling problem,and the influences of macroscopic parameters on the jet coiling are discussed.The numerical results show that the SPH_CS_SP method has higher accuracy and better stability than the traditional SPH method and other corrected SPH method,and can improve the tensile instability.     

Electrospinning Instabilities in the Drop Formation and Multi-Jet Ejection Part II: Various Nozzle Diameters for PVA (Polyvinyl Alcohol) Polymer Solution

Electrospinning is recognized as a simple and easy method to produce fibers with nanoscale diameters. However, the methods for controlling the shape, structure, and uniformity of electrospun fibers have not yet been fully investigated. In this research, the electrospinning jet behavior, corresponding nanofiber deposition, and average fiber diameter are examined for various nozzle diameters. Fluctuations in the sequence of drop growing, electrospinning, and/or termination of electrospinning are analyzed. We propose two different fluctuations according to nozzle diameter. The multi-jet ejections, that are closely related to the amount of nanoweb deposition and the deposition pattern, are explored.     

Fabricating a reactive surface on the fibroin film by a room-temperature plasma jet array for biomolecule immobilization

A simple dielectric barrier discharge(DBD) jet array was designed with a liquid electrode and helium gas.The characteristics of the jet array discharge and the preliminary polymerization with acrylic acid(AA) monomer were presented.The plasma reactor can produce a cold jet array with a gas temperature lower than 315 K,using an applied discharge power between 6 W and 30 W(V dis × I dis).A silk fibroin film(SFF) was modified using the jet array and AA monomer,and the treated SFF samples were characterized by atomic force microscopy(AFM),scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and contact angle(CA).The deposition rate of the poly acrylic acid(PAA) was able to reach 300 nm/min,and the surface roughness and energy increased with the AA flow rate.The FTIR results indicate that the modified SFF had more carboxyl groups(-COOH) than the original SFF.This latter characteristic allowed the modified SFF to immobilize more quantities of antimicrobial peptide(AP,LL-37) which inhibited the Escherichia coli(E.Coli) effectively.     

Influence of morphology on the emissive properties of dye-doped PVP nanofibers produced by electrospinning

Dye-doped polymer micro- and nanofibers with tailored light emission properties have great potential for applications in optical, optoelectronic, or photonic devices. In this study, these types of structures were obtained by electrospinning rhodamine 6 G-doped polyvinylpyrrolidone (PVP) using a polymer solution of 10% (mass) concentration in ethanol. Polymer nanofibers with different morphologies (smooth and beaded) and diameters of about 500 nm were obtained using different electrospinning conditions with the same solutions. Fluorescence optical microscopy observations showed that the dye was distributed uniformly in the doped PVP nanofibers. Different shifts were observed when we compared the wavelength of the dye emission band peak of the smooth nanofibers (566 nm) and the wavelength of the dye emission band peak of the beaded fibers (561.5 nm) produced by electrospinning in different conditions with the wavelength of the emission band peak for transparent thin films produced by spin coating (558 nm) using the same polymer solution. This demonstrates that it is possible to tune the optical properties of electrospun dye-doped polymer nanofibers simply by modifying the morphology of the material, i.e., the parameters of the electrospinning process.     

Size-controlled synthesis of Fe2O3 and Fe3O4 nanoparticles onto zeolite by means of a modified activated-coprecipitation method: effect of the HCl concentration during the activation

Tubular nanofibers (TNFs) of vanadium pentoxide (V₂O₅) were synthesized by electrospinning technique using a single spinneret for the first time by controlling the properties of the precursor solution. A partially miscible polymeric solution of vanadium oxytrihydroxide [VO(OH)₃] was produced by hydrolysis of vanadyl acetylacetonate in Poly(vinylpyrrolidone) (PVP). The phase-separated polymer solution formed the core of the electrospun fibers whereas the VO(OH)₃ formed the shell; the core PVP has been removed by controlled heat treatment. The TNFs had an inner diameter ~60?nm and wall thickness ~±100?nm. The capacitive behavior of the V₂O₅ TNFs was studied using cyclic voltammetry and galvanostatic cycling techniques. The studies showed ideal stable supercapacitive characteristics in the electrospun V₂O₅ TNFs.     

Evolution of three-dimensional coherent structures in compressible axisymmetric jet

A high order difference scheme is used to simulate the spatially developing compressible axisymmetric jet. The results show that the Kelvin-Helmholtz instability appears first when the jet loses its stability, and then with development of jet the increase in nonlinear effects leads to the secondary instability and the formation of the streamwise vortices. The evolution of the three-dimensional coherent structure is presented. The computed results verify that in axisymmetric jet the secondary instability and formation of the streamwise vortices are the important physical mechanism of enhancing the flow mixing and transition occurring.     

Electrospinning Instabilities in the Drop Formation and Multi-Jet Ejection Part I: Various Concentrations of PVA (Polyvinyl Alcohol) Polymer Solution

The electrospinning technique has attracted significant research attention because of its various potential applications and simplicity of manufacturing fibers of diameter from several micrometers to nanometer range. However, the methods for controlling the shape, structure, and uniformity of electrospun fibers have not yet been fully investigated. In this research electrospinning instabilities, such as cyclical electrospinning fluctuation and multi-jet ejections, which are closely related to the corresponding nanofiber deposition, were investigated for various polymer solution concentrations. The cyclical electrospinning fluctuation was evaluated with an image analysis program integrated with an image acquisition system that we developed. Two different drop size fluctuations of the cyclical process of the drop formation were observed.