Elsevier

Polymer

Volume 45, Issue 6, March 2004, Pages 2017-2030
Polymer

Experimental investigation of the governing parameters in the electrospinning of polymer solutions

https://doi.org/10.1016/j.polymer.2004.01.024Get rights and content

Abstract

In the electrospinning process, polymer nanofibers with submicron-scale diameters are formed when a droplet of a viscoelastic polymer solution is subjected to a high voltage electrostatic field. We report the experimental work on the electrospinning process in which the influence of different process parameters on the electric current and volume and surface charge density in the polymer jet was measured. Shear viscosity, surface tension, relaxation time, and the electric conductivity and permittivity were measured as well. For this purpose different solutions of polyethylene oxide (PEO), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyurethane (PU) and polycaprolactone (PCL) were prepared and underwent electrospinning. The governing parameters investigated were the applied voltage (V), the solution flow rate (Q), the polymer weight concentration (C), the molecular weight of the polymer (M), the nozzle-to-ground distance (H) and, in some solutions, the concentration of ethanol (Cet).

Introduction

Electrospinning is a straightforward method to produce nanofibers from polymer solutions in a wide submicron range around 100 nm [1], [2], [3], [4]. The interest in the behavior of thin liquid jets in electric fields dates back to the work of Rayleigh [5]. Taylor [6], [7], [8], [9] produced useful experimental evidence on the conical shape of the protrusion from which a jet sometimes leaves the surface of a pendant liquid drop. A series of papers [10], [11], [12], [13], [14], [15], [16], [17] in the electrospraying community have focused on the properties of liquid jets emitted from the Taylor cone. These papers demonstrate that with knowledge of the jet profile and the electric current it is possible to determine the volume charge density that enables an estimation of the electric field acting on the fluid boundary.

In electrospun jets emitted from Taylor cones, bending instability develops due to the mutually repulsive forces resulting from the electric charges of the jets [1], [2]. Physical models [1], [2], [18], [19], [20], [21] which examine the jet profile, the stability of the jet paths and the cone-like surfaces from which the jets emerge have been developed. In addition, it has been shown that capillary instability, resulting from surface tension, is typically prevented by the strong stabilizing influence of viscoelastic stresses [22] in the electrospinning of polymer solutions. With the recent revival of interest in electrostatic fiber spinning, there has been a number of innovative ideas that are being investigated, such as: electrically conductive nanofibers [23], nanofibrous membranes for the development of high performance batteries [24], piezoelectric nanofibrous devices [25], alignment of electrospun nanofibers [3], [26], [27], [28], electrospun nanofiber crossbars [29], nanotubes [30], nanofiber composites [31], [32], electrospun mats for fine filtration [33], wound dressing [34], and fabrication of tubular products to serve as blood vessel prosthesis [26]. Development of useful applications requires a thorough knowledge of the parameters of the electrospinning process and their effect on the final product.

In the present work we report the results of a systematic investigation of the effect of variation of the governing parameters on the electrospinning of PEO, PAA, PVA, PU and PCL solutions. The parameters investigated include: solution volumetric flow rate, polymer weight concentration and molecular weight, the applied voltage and the nozzle-to-ground distance. In addition, when using PEO solutions, we investigated the effect of the varying ethanol concentration in the solvent. The experimental setup and procedure are discussed in Section 2. This is followed in Section 3 by a presentation and discussion of the results obtained. A summary is provided in Section 4.

Section snippets

Materials

Polyethylene oxide (PEO, molecular weight M=6×105; 106; 4×106 g/mol), polyvinyl alcohol (PVA, M=104g/mol), polyacrylic acid (PAA, M=2.5×105; 4.5×105 g/mol), polyurethane (PU, Tecoflex) and polycaprolactone (PCL, M=8×104g/mol) purchased from Aldrich were used to prepare solutions that were used as the working fluids. PEO, PVA and PAA were dissolved in an ethanol/water solvent at different concentrations. PU was dissolved in tetrahydrofuran (THF) and ethanol. PCL was dissolved in acetone and also

Results and discussion

The electric current and the volume charge density display the same behavior with respect to all the investigated governing parameters except the solution flow rate.

Summary

The relevant physical parameters were measured for a number of polymer solutions (PEO, PAA, PVA, PU and PCL in different solvents) used in the electrospinning of polymer nanofibers. The experiments were undertaken to determine variation of the electric current (I) and volume charge density (ρ) in response to changes in the governing parameters of the process. In the case of one PCL solution the surface charge density q was determined as well. The governing parameters investigated include the

References (47)

  • A.L. Yarin et al.

    On bending instability in electrospinning of nanofibers

    J Appl Phys

    (2001)
  • A. Theron et al.

    Electrostatic field-assisted alignment of electrospun fibers

    Nanotechnology

    (2001)
  • M. Bognitzki et al.

    Nanostructured fibers via electrospinning

    Adv Mater

    (2001)
  • Strutt

    On the equilibrium of liquid conducting masses charged with electricity, London, Edinburgh, Dublin

    Philos. Mag.

    (1882)
  • G.I. Taylor

    Disintegration of water drops in an electric field

    Proc R. Soc. London, Ser. A

    (1964)
  • G.I. Taylor

    Stability of a horizontal liquid interface

    J Fluid Mech

    (1965)
  • G.I. Taylor

    The force exerted by an electric field on a long cylindrical conductor

    Proc. R. Soc. London, Ser. A

    (1966)
  • G.I. Taylor

    Electrically driven jets

    Proc R. Soc. London, Ser. A

    (1969)
  • J.R. Melcher et al.

    Electrohydrodynamics of a current-carrying semi-insulating jet

    J Fluid Mech

    (1971)
  • A.M. Ganan-Calvo

    On the theory of electrohydrodynamically driven capillary jets

    J Fluid Mech

    (1997)
  • I. Hayati et al.

    Investigation into the mechanisms of electrohydrodynamic spraying of liquids. Effect of electric field and environment on pendant drops and factors affecting the formation of stable jets

    J Colloid Interface Sci

    (1987)
  • L.T. Cherney

    Structure of Taylor cone jets: limit of low flow rates

    J Fluid Mech

    (1999)
  • J. Fernandez de la Mora et al.

    The current emitted by highly conducting Taylor cones

    J Fluid Mech

    (1994)
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