Defining the electrospinning window through solvent effects on extensional rheology

Ultrafine fibers produced by electrospinning are quickly becoming a frontrunner for functional fiber applications. Expanding the application field for ultrafine fibers necessitates knowledge of the behavior of polymer solutions during the electrospinning process. In this new application field, more complex fluids outside of the typical scope of electrospinnable solutions are required. These fluids have viscoelastic stresses and microstructural transitions that affect the flow, which may not be quantifiable in shear rheology. Hence, an analysis of the extensional rheology is required to fully characterize the behavior of the electrospinning jet. In this work, we study polymer solutions typically used in electrospinning (low and high MW PVP in methanol and water, and PEO and PVA in water). We see that the solutions differ in their extensional rheological behavior, especially with respect to surface tension which shows a strong effect on fiber formation. High surface tension solvents require higher extensional viscosities and relaxation times to form smooth fibers. Global dimensionless numbers such as the Deborah and Ohnesorge numbers appear to be a promising method of quantifying electrospinnability. Defining the electrospinning processing window through extensional rheology allows for more rational design of advanced ultrafine fibers for future applications.