(706a) Free Surface Electrospinning From a Wire Electrode

The needle or nozzle-based electrospinning process has long been explored for its capability to produce unique nanofiber materials with desirable properties such as high surface area and high porosity. These materials are of interest in a wide range of fields such as textiles, filtration, tissue engineering, drug delivery systems, nanocomposites, and alternative-energy generation systems such as solar cells, fuel cells, and energy storage devices. However, one of the perceived drawbacks of the method for industrial purposes is its low production rate. A typical production rate from a single spinneret is 0.1 -1 g of fiber per hour, depending on the solution properties and operating parameters. To overcome the low productivity of nozzle-based electrospinning, we consider “free surface electrospinning” (also referred to as “needleless electrospinning”) where electrohydrodynamic jets self-organize spontaneously on a free liquid surface. It has been estimated that the concentration of the jets can be increased by an order of magnitude or more compared to conventional electrospinning by employing free surface electrospinning.  

In this report, we analyze free surface electrospinning from a thin wire electrode. In this process, metal wire electrodes mounted on a spindle are drawn through an electrified fluid bath in a direction perpendicular to the wire axes. As a wire moves through the fluid/air interface, fluid is entrained on the wire, resulting in a thin film of fluid coating the wire. Due to a Plateau-Rayleigh instability, the coating breaks up into individual droplets of charged fluid on the metal wire. At sufficiently high local electric field, the individual drops deform and jets are produced from the droplets, giving rise to a form of free surface electrospinning. As the spindle rotates, electrospinning continues to occur until the supply of fluid is exhausted or the required electric field conditions are no longer met. By mounting several wires on a rotating spindle, the process of immersion, entrainment, dewetting and jetting can be performed repeatedly in a simple manner.

The processes of charging, entrainment, droplet breakup, and jetting are all coupled in this process.  Here we examine how the fluid properties (i.e. surface tension, viscosity, density, concentration) and wire electrode rotation rate affect fluid entrainment and drop breakup. Applied potential and rotation rate of the spindle are varied to study the effects of these operating parameters. Current measures are preformed to examine the effects of fluid properties and operating parameters on the fluid charge density. The productivity is determined for a range of applied voltages and electrode rotation rates and compared to the theoretical limit of fluid entrainment. In addition, scanning electron micrographs are used to investigate the fiber diameter and distribution of the electrospun mats.