Increasing ionic conductivity within thermoplastics melts via commercial additives to enable mesoscale fiber formation from melt electrospinning*

Electrospinning is a nanofiber formation process that relies on the interaction between ions in a polymer fluid (solution or melt) and an applied electric field. Although fibers produced from melts are expected to have superior mechanical properties (compared to those from solutions), melt electrospinning is notoriously unpopular:  the higher viscosity of melts makes it difficult to feed fluid through a narrow needle and is often blamed for large fiber diameters.  On the other hand, the role of low ionic conductivity in thermoplastic melts as a barrier to nanofiber formation has been underexplored. We used an unconfined configuration (i.e., needle-free) that mitigates the practical challenges of high viscosity and enables a fundamental study of the length scales impacted by viscosity and those altered by conductivity*. Two polyethylene formulations with different viscosities were utilized and a chemically-compatible commercial anti-static agent was used to introduce additional ionic conductivity. The key role of conductivity in determining the jet radius (which sets the upper limit on the fiber size) is discussed in the context of fluid mechanics theory and previous simulations.  Increased conductivity resulted in a 20× decrease in fiber diameter and formation of a significant fraction of sub-micron diameter fibers.  Parameters which affect the conversion of the liquid jet to a solid fiber and the pertinent theory are also outlined.  *Soft Matter, 2021, DOI: 10.1039/D1SM01101D