Influence of Polymer Relaxation Time on the Electrospinning Process: Numerical Investigation.

Siddharth Gadkari

doi:10.3390/polym9100501

Abstract

“Electrospinnability”, or the ease with which a solution can be used to obtain bead-free uniform fibers, depends on a large number of parameters, including solution properties, process parameters and ambient conditions. In this study, the effect of the polymer relaxation time on electrospinning of dilute polymer solutions is investigated numerically. It is shown that elastic stresses (ES) increase exponentially with the Deborah number (). For each polymer concentration there exists a critical below which the ES are insufficient to overcome capillary stresses (CS) and lead to the formation of beaded fibers. However, above the critical , there is a higher probability of the ES overcoming the CS and leading to the formation of uniform fibers. This analysis suggests the possibility of improved electrospinnability even with dilute polymer solutions, provided the relaxation time is sufficiently large. It is also found that changes in the drag coefficient due to change in the polymer conformation and self-concentration of polymer molecules would become significant for the electrospinning of polymer solutions with a longer relaxation time and high conductivity.

Highlights

Electrospinning is a simple and versatile method to produce polymeric nanofibers
The jet first undergoes rapid thinning starting from the nozzle up to the Taylor cone region
The local strain rate or Wi+ increases rapidly in this region and grows beyond the critical value of 0.5 for the coil–stretch transition of polymer molecules. This fact is highly important for dilute polymer solutions, as no such transition can be observed in semi-dilute solutions

Summary

Introduction

Electrospinning is a simple and versatile method to produce polymeric nanofibers. A typical electrospinning setup only requires a spinneret (syringe pump, syringe and a flat tip needle), a high voltage power supply and a collector plate, which is usually a conductor [1]. The jet follows a straight path for a certain distance but soon succumbs to numerous electrohydrodynamic instabilities, the most dominant being the whipping instability, which results in rapid chaotic movement of the jet in concentric circles of increasing diameter. This results in extensive elongation and extreme thinning of the jet. As the jet moves down, it dries and solidifies and is deposited on the collector [3]

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Results

Conclusion