Jet initiation and thinning in electrospinning depends on the charges carried by the jet. However, the same charges that stretches the jet often becomes a liability once the fibers are deposited on the collector as it tends to repel later fibers. This may result in the formation of fiber layers, increased wastage or difficulty in obtaining thicker membrane. There are several ways of reducing the level of residual charges.
A corona discharge apparatus may be used to generate neutralizing ions. Depending on the position of the corona discharge apparatus, it may be used to reduce electrospinning jet repulsions for multiple spinnerets setup if it is placed between the collector and spinnerets [Tsai P et al 2003]. However, an optimum level of neutralizing ions need to be found as excessive neutralizing ions may cause premature stoppage in jet elongation (due to neutralizing of the charges on the jet) resulting in beaded fibers [Fong H et al 1999]. To avoid neutralization of the charges on the electrospinning jet prior to deposition on the collector, position a rotating collector between the electrospinning jet and the corona discharge apparatus such that fiber deposition is on one face of the collector and charge neutralization on the opposing face. This setup has been shown to be very effective in encouraging fibers to deposit on the collector even for non-conducting fabrics [Uecker J C et al 2010]. Charge neutralization may not be restricted to after the fibers are deposited on the collector. It may be initiated during the electrospinning jet flight. Korkut et al (2008) found that in a higher humidity environment, gas ionization increases and has been found to reduce the amount of charges carried by the electrospinning jet. Kim et al (2009) used an AC electric field of 2 - 5 kV/cm at 300 Hz on steering electrodes to control the electrospinning jet and it was found that the overall charges on the deposited fibers were reduced. Although it is not clear why a high AC voltage applied to steering electrodes lead to a reduction on the charges, this may also be due gas ionization at the steering electrodes which neutralizes the charges on the electrospinning jet.
Both positive and negative high voltages can be used for electrospinning. By simultaneously electrospinning with both polarities on the same collector, the amount of residual charges is expected to be reduced due to charge neutralization. Tong et al uses positive and negatively charged electrospinning jet to deposit fibers on rotating drums [Tong et al 2013]. To prevent the collision of the opposing charged jets, they erected a barrier between the two collection drums. The drums were rotated such that alternate positive and negative charged nanofibers were collected. With this, they were able to buildup membrane with thickness of over 300 um compared to less than 200 um from conventional single jet electrospinning setup.
Published date: 12 March 2014
Last updated: 29 July 2014
▼ Reference
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Fong H, Chun I, Reneker D H. Beaded nanofibers formed during electrospinning. Polymer 1999; 40: 4585.
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Kim G H, Yoon H, Lee H N, Park G M. Polycarprolactone Ultrafine Fiber Membrane Fabricated Using a Charge-reduced Electrohydrodynamic Process. Macromolecular Research 2009; 17: 533.
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Korkut S, Saville D A, Aksay I A. Enhanced Stability of Electrohydrodynamic Jets through Gas Ionization. Physical Review Letters 2008; 100: 034503.
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Tong H W, Wang M. A novel technique for the fabrication of 3D nanofibrous scaffolds using simultaneous positive voltage electrospinning and negative voltage electrospinning. Materials Letters 2013; 94: 116
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Tsai P, Schreuder-Gibson H L. The Role of Fiber Charging on Co-electrospinning and the Resident Life of the Residual Charges from the Electrospinning Process. Presented at the American Filtration and Separations Society Spring 2003 Meeting.
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Uecker J C, Tepper G C, Rosell-LIompart J. Ion-assisted collection of Nylon-4,6 electrospun nanofibers. Polymer 2010; 51: 5221.
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