Branching jet splitting off from main jet when there is excess solution. [Abdel-Hady et al. ISRN Nanotechnology, vol. 2011, Article ID 851317, 14 pages, 2011. doi:10.5402/2011/851317. This work is licensed under a Creative Commons Attribution 3.0 Unported License.]
Electrospinning is known to produce fibers down to nanometer diameter through solution elongation under the force of electrostatic repulsion. Bending instability of the electrospinning jet is generally accepted as the mechanism which allows thinning of the solution jet to such small dimension. Although the distance between the needle tip and the collector is relatively short, the bending instability causes the jet to travel over a much larger distance. However, there is another mechanism that may contribute to nanofiber formation in electrospinning and that is the ejection of branched jets from the primary electrospinning jet. Branching or splitting jet may provide a logical explanation to the length of fibers obtained in relation to the jet speed. If electrospinning is just a single jet, the velocities of some electrospun solution would theoretically reached tens of thousands of meters per minute [Wang et al 2006] which is unlikely.
Youtube video on electrospinning with secondary/splitted jets
Branching has been observed to form both on the straight and bending part of the primary jet. In a model developed by Yarin et al (2005) to explain the observation of branching in electrospinning jet, this phenomenon is caused by "static equilibrium undulations under the combined effects of the electric Maxwell stresses and surface tension as the electrical stresses increase". The undulated electrospinning jet contains segments with high curvature and concentration of charges on these sites favours the emanation of lateral branches. Parameters that increases the undulations and electrical interactions between the jet and the electric field may potentially encouraged the formation of secondary branches.
The electrospinning solution property has an influence on the formation of branching electrospinning jets. Wang et al (2006) noticed that with reduced solution concentration, branched fibers were observed. Zhao et al (2004) proposed that at higher concentration, greater chain entanglement discourages jets from splitting off. Solution with higher surface tension may also discourage jets from splitting off.
Excessive feed-rate may result in greater solution volume being drawn from the nozzle tip during electrospinning. The increased radius of the electrospinning jet increases the surface area where branching jets split off [Abdel-Hardy et al 2011]. A larger electrospinning jet may also be more unstable leading to greater undulations on its surface []Yarin et al 2005].
Greater branching was also observed at elevated spinning environment. While the branching or splitting of electrospinning jet is probably due to instability in the jet and non-uniform distribution of the charges along the jet, spinning in an elevated temperature environment may facilitate this occurrence [Amiraliyan et al 2009].
Abdel-Hady, Alzahrany A, Hamed M. Experimental Validation of Upward Electrospinning Process. ISRN Nanotechnology 2011; 2011: 851317.
Amiraliyan N, Nouri M, Kish M H. Effects of Some Electrospinning Parameters on Morphology of Natural Silk-Based Nanofibers. J Appl Polym Sci 2009; 113: 226.
Wang X W, Cao J, Hu Z M, Pan W L, Liu Z F. Jet Shaping Nanofibers and the Collection of Nanofiber Mats in Electrospinning. J. Mater. Sci. Technol. 2006; 22: 536.
Open Access
Yarin A L, Kataphinan W, Reneker D H. Branching in electrospinning of nanofibers. Journal of Applied Physics 2005; 98: 064501.
Zhao S L, Wu X H, Wang L G, Huang Y. Electrospinning of Ethyl-Cyanoethyl Cellulose/Tetrahydrofuran Solutions. J. Appl. Polym. Sci. 2004; 91: 242.
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