ABSTRACT
Electrospinning is one of the few known methods of creating nanoscale fibers. Nanoscale fibers are attractive materials for their superior surface area-tovolume ratio, making it ideal for important applications. As illustrated in Figure 1, a high-voltage electrode is placed in contact with the polymer solution contained in a pipette or syringe-like vessel with a capillary tip. This electrode provides a source of charge. The ground electrode of the high-voltage source is attached to collector plate, which serves as a target for the electrostatically driven polymer fluid stream. The potential difference between the capillary tip and the ground is typically on the order of 10-30 kV.[1-3]
At a sufficiently high potential difference, the electrostatic stresses overcome the surface tension of the Taylor cone. Then, a stream of polymer fluid is ejected and is propelled toward the grounded target. As the ejected stream forms a filament that traverses the distance from the Taylor cone at the capillary tip to the grounded target, the solvent component is lost by evaporation processes and the remaining polymer solidifies into a coherent filament. The motion of the filament is straight for a relatively short distance and then becomes erratic due to an electric field-induced bending instability. The re-
sult of this dynamic process is a nonwoven filament mat that collects on the grounded target.[4-5]
The advantages of electrospinning over the other methods of nanofiber fabrication are its ease of manufacture and simple fabrication tools required. And the disadvantages of electrospinning are the lack of control of the final product with respect to fiber diameter, uniformity, and morphology. The inherent instability of the process makes its lack of repeatability problematic. Although much research has been done in the process itself, its wide-scale adoption has been inhibited by a lack of predictive control on the fiber properties. By developing an accurate computational model, enhanced process control and the production of fibers with desired properties can be attained. Electrospinning is an example of an electrohydrodynamic (EHD) phenomenon. In EHDs, charges induce fluid motion within an electric field. During the process, the transport and distribution of these charges generate stresses that result in the movement of the fluid. The leaky dielectric EHD model is an appropriate model to use because the model of the fluid’s electrical properties as a poorly conducting liquid is comparable to the behavior of most polymer solutions, the most commonly used type of fluid in electrospinning.[6-7] But it does not take thermal effect into account. For a polymer with high molten temperature, thermal factor is critical for the process. Hence, a rigorous thermo-electro-hydrodynamics description of electrospinning is needed for better understanding of the process.[8] This study establishes a mathematical model to explore the physics behind electrospinning.
