Dr. Keith Forward, Massachusetts Institute of Technology
January 27, 2012
11:00 AM - 12:00 PM
Free Surface Electrospinning from a Wire Electrode
Abstract:
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. A bench-top apparatus was analyzed where free surface electrospinning occurs from a thin wire electrode. In this process, metal wire electrodes mounted on a spindle are drawn through an electrified liquid bath in a direction perpendicular to the wire axes. As a wire moves through the fluid/air interface, liquid is entrained on the wire, resulting in a thin film of liquid coating the wire. Due to a Plateau-Rayleigh instability, the coating breaks up into individual droplets of charged liquid 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 liquid 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. We examine how the liquid properties (i.e. surface tension, viscosity, density, concentration) and wire electrode rotation rate affect liquid entrainment and droplet breakup. Applied potential and rotation rate of the spindle are varied to study the effects of these operating parameters. A model for the productivity of the process is presented to account for liquid properties and operating parameters. Based upon the presented productivity model, a small pilot-plant scale apparatus was designed and built. The apparatus has the capability of producing 200 g of fiber per hour, depending on liquid properties and operating parameters. This study shows the ease of scaling up free surface electrospinning, and the capability of industrializing electrospinning.
Date posted
Jun 17, 2019
Date updated
Jun 17, 2019