Experimental investigation of the governing parameters in the electrospinning of polymer solutions
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, ), polyacrylic acid (PAA, M=2.5×105; 4.5×105 g/mol), polyurethane (PU, Tecoflex) and polycaprolactone (PCL, ) 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)
- et al.
Current and droplet size in the electrospraying of liquids: scaling laws
J Aerosol Sci
(1997) The surface charge in electrospraying: its nature and its universal scaling laws
J Aerosol Sci
(1999)Electrohydrodynamics of electrified liquid menisci and emitted jets
J Aerosol Sci
(1999)- et al.
Electrostatically-generated nanofibers of electronic polymers
Synth Met
(2001) - et al.
Electrostatic fabrication of ultrafine conducting fibers: polyaniline/polyethylene oxide blends
J Synth Metals
(2000) - et al.
Controlled deposition of electrospun polyethylene oxide fibers
Polymer
(2001) - et al.
Electrospinning process and applications of electrospun fibers
J Electrostatics
(1995) - et al.
Electrospinning of polyurethane fibers
Polymer
(2002) - et al.
Nanofiber garlands of polycaprolactone by electrospinning
Polymer
(2002) - et al.
Bending instability of electrically charged liquid jets of polymer solutions in electrospinning
J Appl Phys
(2000)