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Darrell H Reneker - One of the best experts on this subject based on the ideXlab platform.

  • effect of evaporation and solidification of the charged jet in electrospinning of poly ethylene oxide aqueous solution
    Polymer, 2007
    Co-Authors: Sureeporn Tripatanasuwan, Zhenxin Zhong, Darrell H Reneker
    Abstract:

    The electrospinning process uses electrical force to produce nanofibers. A charged droplet acquires a conical shape known as the Taylor cone and then becomes unstable. A charged jet emerges from the vertex and develops a spiral path due to the electrically driven Bending Instability, which makes it possible, in a small space, for the jet to elongate by a large amount and produce nanofibers. Evaporation and the associated solidification were identified as important factors that affect the diameter of electrospun nanofibers. In this study, the evaporation rate and solidification of the charged jet were controlled by varying the relative humidity during electrospinning of poly(ethylene oxide) from aqueous solution. As the relative humidity increased, the solidification process became slower, allowing elongation of the charged jet to continue longer and thereby to form thinner fibers. As the relative humidity increased from 5.1% to 48.7%, the diameter of the solidified fiber decreased from 253 nm to 144 nm. As the relative humidity increased above 50%, beads formed on the thinner fibers, indicating that the capillary Instability occurred before the jet solidified. The vapor concentration of solvent is an effective electrospinning process control parameter of fiber diameter that also produces a systematic change in the development of beads on the fibers.

  • nanofiber garlands of polycaprolactone by electrospinning
    Polymer, 2002
    Co-Authors: Darrell H Reneker, Woraphon Kataphinan, A Theron, Eyal Zussman, Alexander L Yarin
    Abstract:

    Abstract Over a period of time, the typical path of a single jet of polymer solution, in the electrospinning process follows the nearly straight electric field lines for a certain distance away from the tip, and then develops a series of electrically driven Bending instabilities that cause the path of the jet to explore a cone shaped envelope as the jet elongates and dries into a nanofiber. The multitudes of open loops that are formed are rarely observed to come into contact with each other until the dry nanofiber is collected at the end of the process. A new phenomenon is reported in this paper. Electrospinning a solution of polycaprolactone in acetone caused the dramatic appearance of a fluffy, columnar network of fibers that moved slowly in large loops and long curves. The name ‘garland’ was given to the columnar network. Open loops of the single jet came into contact just after the onset of the Bending Instability and then merged into a cross-linked network that created and maintained the garland. Contacts between loops occurred when the plane of some of the leading loops of the jet rotated around a radius of the loop. Then a small following loop, expanding in a different plane, intersected a leading loop that was as many as several turns ahead. Mechanical forces overcame the repulsive forces from the charge carried by the jet, the open loops in flight made contact and merged at the contact point, to form closed loops. The closed loops constrained the motion to form a fluffy network that stretched and became a long roughly cylindrical column a few millimeters in diameter. This garland, which was electrically charged, developed a path of large open loops that are characteristic of a large-scale electrically driven Bending Instability. Over a long period of time, the fluffy garland never traveled outside a conical envelope similar to, but larger than the conical envelope associated with the Bending Instability of a single jet.

  • Bending Instability in electrospinning of nanofibers
    Journal of Applied Physics, 2001
    Co-Authors: Alexander L Yarin, Sureeporn Koombhongse, Darrell H Reneker
    Abstract:

    A localized approximation was developed to calculate the Bending electric force acting on an electrified polymer jet, which is a key element of the electrospinning process for manufacturing of nanofibers. Using this force, a far reaching analogy between the electrically driven Bending Instability and the aerodynamically driven Instability was established. Continuous, quasi-one-dimensional, partial differential equations were derived and used to predict the growth rate of small electrically driven Bending perturbations of a liquid column. A discretized form of these equations, that accounts for solvent evaporation and polymer solidification, was used to calculate the jet paths during the course of nonlinear Bending Instability leading to formation of large loops and resulting in nanofibers. The results of the calculations are compared to the experimental data acquired in the present work. Agreement of theory and experiment is discussed.

  • Bending Instability of electrically charged liquid jets of polymer solutions in electrospinning
    Journal of Applied Physics, 2000
    Co-Authors: Darrell H Reneker, Alexander Yarin, Hao Fong, Sureeporn Koombhongse
    Abstract:

    Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the Instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven Bending Instability. The three-dimensi...

  • Bending Instability of electrically charged liquid jets of polymer solutions in electrospinning
    Journal of Applied Physics, 2000
    Co-Authors: Darrell H Reneker, Hao Fong, Alexander L Yarin, Sureeporn Koombhongse
    Abstract:

    Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the Instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven Bending Instability. The three-dimensional paths of continuous jets were calculated, both in the nearly straight region where the Instability grew slowly and in the region where the Bending dominated the path of the jet. The mathematical model provides a reasonable representation of the experimental data, particularly of the jet paths determined from high speed videographic observations.

Sureeporn Koombhongse - One of the best experts on this subject based on the ideXlab platform.

  • Bending Instability in electrospinning of nanofibers
    Journal of Applied Physics, 2001
    Co-Authors: Alexander L Yarin, Sureeporn Koombhongse, Darrell H Reneker
    Abstract:

    A localized approximation was developed to calculate the Bending electric force acting on an electrified polymer jet, which is a key element of the electrospinning process for manufacturing of nanofibers. Using this force, a far reaching analogy between the electrically driven Bending Instability and the aerodynamically driven Instability was established. Continuous, quasi-one-dimensional, partial differential equations were derived and used to predict the growth rate of small electrically driven Bending perturbations of a liquid column. A discretized form of these equations, that accounts for solvent evaporation and polymer solidification, was used to calculate the jet paths during the course of nonlinear Bending Instability leading to formation of large loops and resulting in nanofibers. The results of the calculations are compared to the experimental data acquired in the present work. Agreement of theory and experiment is discussed.

  • Bending Instability of electrically charged liquid jets of polymer solutions in electrospinning
    Journal of Applied Physics, 2000
    Co-Authors: Darrell H Reneker, Alexander Yarin, Hao Fong, Sureeporn Koombhongse
    Abstract:

    Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the Instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven Bending Instability. The three-dimensi...

  • Bending Instability of electrically charged liquid jets of polymer solutions in electrospinning
    Journal of Applied Physics, 2000
    Co-Authors: Darrell H Reneker, Hao Fong, Alexander L Yarin, Sureeporn Koombhongse
    Abstract:

    Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the Instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven Bending Instability. The three-dimensional paths of continuous jets were calculated, both in the nearly straight region where the Instability grew slowly and in the region where the Bending dominated the path of the jet. The mathematical model provides a reasonable representation of the experimental data, particularly of the jet paths determined from high speed videographic observations.

Alexander L Yarin - One of the best experts on this subject based on the ideXlab platform.

  • upward needleless electrospinning of multiple nanofibers
    Polymer, 2004
    Co-Authors: Alexander L Yarin, Eyal Zussman
    Abstract:

    A new approach to electrospinning of polymer nanofibers is proposed. A two-layer system, with the lower layer being a ferromagnetic suspension and the upper layer a polymer solution, is subject to a normal magnetic field provided by a permanent magnet or a coil. As a result, steady vertical spikes of magnetic suspension perturbed the interlayer interface, as well as the free surface of the uppermost polymer layer. When a normal electric field is applied in addition to the system, the perturbations of the free surface become sites of jetting directed upward. Multiple electrified jets undergo strong stretching by the electric field and Bending Instability, solvent evaporates and solidified nanofibers deposit on the upper counter-electrode, as in an ordinary electrospinning process. However, the production rate is shown to be higher.

  • nanofiber garlands of polycaprolactone by electrospinning
    Polymer, 2002
    Co-Authors: Darrell H Reneker, Woraphon Kataphinan, A Theron, Eyal Zussman, Alexander L Yarin
    Abstract:

    Abstract Over a period of time, the typical path of a single jet of polymer solution, in the electrospinning process follows the nearly straight electric field lines for a certain distance away from the tip, and then develops a series of electrically driven Bending instabilities that cause the path of the jet to explore a cone shaped envelope as the jet elongates and dries into a nanofiber. The multitudes of open loops that are formed are rarely observed to come into contact with each other until the dry nanofiber is collected at the end of the process. A new phenomenon is reported in this paper. Electrospinning a solution of polycaprolactone in acetone caused the dramatic appearance of a fluffy, columnar network of fibers that moved slowly in large loops and long curves. The name ‘garland’ was given to the columnar network. Open loops of the single jet came into contact just after the onset of the Bending Instability and then merged into a cross-linked network that created and maintained the garland. Contacts between loops occurred when the plane of some of the leading loops of the jet rotated around a radius of the loop. Then a small following loop, expanding in a different plane, intersected a leading loop that was as many as several turns ahead. Mechanical forces overcame the repulsive forces from the charge carried by the jet, the open loops in flight made contact and merged at the contact point, to form closed loops. The closed loops constrained the motion to form a fluffy network that stretched and became a long roughly cylindrical column a few millimeters in diameter. This garland, which was electrically charged, developed a path of large open loops that are characteristic of a large-scale electrically driven Bending Instability. Over a long period of time, the fluffy garland never traveled outside a conical envelope similar to, but larger than the conical envelope associated with the Bending Instability of a single jet.

  • Bending Instability in electrospinning of nanofibers
    Journal of Applied Physics, 2001
    Co-Authors: Alexander L Yarin, Sureeporn Koombhongse, Darrell H Reneker
    Abstract:

    A localized approximation was developed to calculate the Bending electric force acting on an electrified polymer jet, which is a key element of the electrospinning process for manufacturing of nanofibers. Using this force, a far reaching analogy between the electrically driven Bending Instability and the aerodynamically driven Instability was established. Continuous, quasi-one-dimensional, partial differential equations were derived and used to predict the growth rate of small electrically driven Bending perturbations of a liquid column. A discretized form of these equations, that accounts for solvent evaporation and polymer solidification, was used to calculate the jet paths during the course of nonlinear Bending Instability leading to formation of large loops and resulting in nanofibers. The results of the calculations are compared to the experimental data acquired in the present work. Agreement of theory and experiment is discussed.

  • Bending Instability of electrically charged liquid jets of polymer solutions in electrospinning
    Journal of Applied Physics, 2000
    Co-Authors: Darrell H Reneker, Hao Fong, Alexander L Yarin, Sureeporn Koombhongse
    Abstract:

    Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the Instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven Bending Instability. The three-dimensional paths of continuous jets were calculated, both in the nearly straight region where the Instability grew slowly and in the region where the Bending dominated the path of the jet. The mathematical model provides a reasonable representation of the experimental data, particularly of the jet paths determined from high speed videographic observations.

Robert L Clark - One of the best experts on this subject based on the ideXlab platform.

  • electric field effects on fiber alignment using an auxiliary electrode during electrospinning
    Scripta Materialia, 2009
    Co-Authors: Lisa S Carnell, Emilie J Siochi, Russell A Wincheski, Nancy M Holloway, Robert L Clark
    Abstract:

    Control of electrospun fiber placement and distribution was investigated by examining the effect of electric field parameters on the electrospinning of fibers. The experimental set-up used in this study eliminated the Bending Instability and whipping, allowing the jet to be modeled as a stable trajectory. Coupling of experimental and computational results suggests the potential for predicting aligned fiber distribution in electrospun mats.

Hao Fong - One of the best experts on this subject based on the ideXlab platform.

  • Bending Instability of electrically charged liquid jets of polymer solutions in electrospinning
    Journal of Applied Physics, 2000
    Co-Authors: Darrell H Reneker, Alexander Yarin, Hao Fong, Sureeporn Koombhongse
    Abstract:

    Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the Instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven Bending Instability. The three-dimensi...

  • Bending Instability of electrically charged liquid jets of polymer solutions in electrospinning
    Journal of Applied Physics, 2000
    Co-Authors: Darrell H Reneker, Hao Fong, Alexander L Yarin, Sureeporn Koombhongse
    Abstract:

    Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the Instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven Bending Instability. The three-dimensional paths of continuous jets were calculated, both in the nearly straight region where the Instability grew slowly and in the region where the Bending dominated the path of the jet. The mathematical model provides a reasonable representation of the experimental data, particularly of the jet paths determined from high speed videographic observations.