Electrospinning Jet Research Articles

A correlation for the diameter of electrospun polymer nanofibers

AbstractA rational method to control morphology of polymer nanofibers produced by electrospinning is developed using dimensional analysis of the electrospinning process. The analysis is validated against data sets from the literature, which provides an empirical correlation between fiber size, controllable operating conditions, and measurable spinning solution properties. A stable jet operating regime is identified for which scaling of dimensionless groups is presented. Deviations from this scaling are qualitatively consistent with capillary instability of the electrospinning jet, for which a beaded fiber morphology is obtained. The results provide criteria for designing and controlling electrospinning of polymer solutions and resulting nanofiber morphology. © 2006 American Institute of Chemical Engineers AIChE J, 2007

Thermal and spectroscopic characterization of microbial poly(3‐hydroxybutyrate) submicrometer fibers prepared by electrospinning

AbstractSubmicrometer fibers based on the microbially synthesized ultra‐high‐molecular‐weight poly(3‐hydroxybutyrate) (PHB) were generated by an electrospinning (ES) process with chloroform as the solvent. To characterize the resulting electrospun fibers in comparison with the pure PHB before ES, differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy were performed. The diameters of the electrospun fibers characterized by SEM were in the range 400–1000 nm. Thermal analysis showed that the electrospun fibers contained both helical (α form) and trans‐zigzag (β form) crystals, whereas the solution‐cast PHB films mostly possessed the common helical structure. In addition, the crystallinity of the electrospun PHB fibers increased compared to that of the solution‐cast PHB films. Conformational changes occurred with the high extensional flow in the ES jets. Furthermore, the results from polarized FTIR measurements demonstrate that PHB molecules were oriented parallel to the fiber axis. As a result, the electrospun fibers exhibited strong birefringence under the polarized light. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1860–1867, 2007

Control of an electrospinning jet using electric focusing and jet-steering fields

Electrospinning can be used to deposit a wide variety of nanoscale polymeric fibers that have electrical, optical, or biological properties of interest. While there have been many studies of material properties, the typical deposited nanofibers are in the form of a randomly oriented mat. The authors are interested in forming functional devices utilizing the properties of the individual nanofibers. To this end they have used electric fields to both confine and steer an electrospun polymer jet for controlled deposition of functional materials. They have used an electrode between the electrospinning tip and grounded sample to suppress the chaotic whipping mode, thereby focusing the characteristic spot size of the deposited fibers to a smaller diameter. The same electrode setup was then modified to produce a time-varying steering field. Using this system, they have deposited isolated electrospun polymer fibers in a controlled fashion. They have also demonstrated that it is possible to terminate electrospun fibers using the modulated electric field.

Individually Resolved DNA Molecules Stretched and Embedded in Electrospun Polymer Nanofibers

We have used the flow characteristics of an electrospinning jet to elongate and fix DNA molecules. We embedded and observed fluorescently labeled lambda bacteriophage DNA molecules in polyethylene oxide nanofibers. The embedded DNA molecules were imaged using fluorescence microscopy and found to be stretched to lengths approaching the full dyed contour length.

Solution Rheological Behavior and Electrospinning of Cationic Polyelectrolytes

The influence of polyelectrolyte rheological behavior on the electrospinning process was determined for a series of poly(2-(dimethylamino)ethyl methacrylate hydrochloride) (PDMAEMA·HCl) aqueous solutions in the presence of added NaCl. Solution rheological studies revealed that PDMAEMA·HCl in an 80/20 w/w water/methanol cosolvent displayed polyelectrolyte behavior based on the scaling relationship between specific viscosity (ηsp) and concentration in the semidilute unentangled and semidilute entangled regimes. The entanglement concentration (Ce) increased with NaCl concentration due to screening of the electrostatic repulsive forces along the PDMAEMA·HCl backbone, which enabled the PDMAEMA·HCl chains to adopt a flexible, coillike conformation. Moreover, the scaling behavior in the semidilute entangled regime shifted from polyelectrolyte (ηsp ∼ C1.5) to neutral polymer behavior (ηsp ∼ C3.75) in the high salt limit. The electrospinning performance of PDMAEMA·HCl solutions was also dependent on NaCl concentration, and NaCl-free PDMAEMA·HCl solutions did not form fibers at concentrations less than 8Ce. The minimum concentration for fiber formation decreased as the level of NaCl was increased due to screening of the repulsive, electrostatic interactions between charged repeating units that served to stabilize the electrospinning jet. Moreover, because of the high electrical conductivity of the polyelectrolyte solutions, the electrospun polyelectrolyte fibers were 2−3 orders of magnitude smaller in diameter compared to fibers that were electrospun from solutions of neutral polymers of equal zero shear viscosity (η0) and normalized concentration (C/Ce).

Critical length of straight jet in electrospinning

In this paper the well-known Chauchy's inequality is applied to prediction of critical length of the straight jet in electrospinning. A critical relationship between radius r of jet and the axial distance z from nozzle is obtained for the straight jet. Critical length number and critical radius number are defined, which might be found potential applications in experiment and apparatus design.

Electrospun fibre bundle made of aligned nanofibres over two fixed points

Despite recent advances in electrospinning, creating highly ordered structurethrough the use of electrospun fibres is not possible. This is due to the chaoticmotion of the electrospinning jet which means that the deposition location of thefibres covers a few centimetres radius. As a result, applications for electrospunfibres are restricted to applications where precise positioning is not required.However, through the use of steel blades to control the electric field, it is nowpossible to create a fibre bundle made of highly aligned nanofibres where theends of the fibre bundle are fixed during electrospinning. The creation of highlyordered structures made of electrospun fibre bundles is now possible since the fibrebundle is robust enough to be handled, and it is also easy to transfer the fibrebundle onto a substrate. More importantly, with the two ends of the fibre bundleknown, automating the transfer of the fibre bundle onto a substrate is a possibility.

Multiple jets in electrospinning: experiment and modeling

The electric forces are the main factor responsible for the characteristic jet path and stretching in electrospinning. The present work describes the results of the experimental investigation and modeling of multiple jets during the electrospinning of polymer solutions. Realistic configurations of the external electric field between the electrodes were employed, as well as the linear and non-linear, Upper-Convected Maxwell, models were used to describe the viscoelastic behavior of the polymer jets. The results demonstrate how the external electric fields and mutual electric interaction of multiple charged jets influence their path and evolution during electrospinning.

Effect of the Electrospinning Process on Polymer Crystallization Chain Conformation in Nylon-6 and Nylon-12

Electrospinning of biologically significant polymers (natural and synthetic polypeptides) has increased since electrospun membranes were identified as candidates for tissue engineering constructs. These materials have a specific secondary structure, which influences their properties. The effect of electrospinning on the secondary structure of nylon-6 and nylon-12 is examined using Raman spectroscopy in order to identify and quantify any conformational changes that occur due to processing. Nylon-6 and nylon-12 were chosen because they possess a specific chain conformation and have a backbone chemical structure similar to the amino acid sequence in polypeptides. Results indicate that a change in the chain conformation due to electrospinning occurs, implying that a high stress is induced on the electrospinning jet as the fibers are being formed, and this stress alters the chain conformation of the nylon backbone.

Controlled deposition of electrospun poly(ethylene oxide) fibers

Electrospinning is a process by which sub-micron polymer fibers can be produced using an electrostatically driven jet of polymer solution (or polymer melt). Electrospun fibers are typically collected in the form of non-woven mats, which are of interest for a variety of applications including semi-permeable membranes, filters, composite reinforcement, and scaffolding used in tissue engineering. A characteristic feature of the electrospinning process is the onset of a chaotic oscillation of the electrospinning jet. The current work demonstrates the feasibility of dampening this instability and controlling the deposition of sub-micron polymer fibers (<300 nm in diameter) on a substrate through use of an electrostatic lens element and collection target of opposite polarity. Real-time observations of the electrospinning process have been made using high-speed, high-magnification imaging techniques. Fiber mats and yarns electrospun from polyethylene oxide have been analyzed using wide-angle X-ray diffraction (WAXD), optical microscopy, and environmental scanning electron microscopy (ESEM).