Solvent Effects on the Elasticity of Electrospinnable Polymer Solutions

Abstract

Ultrafine fibers manufactured through electrospinning are a frontrunner for advanced fiber applications, but transitioning from potential to commercial applications for ultrafine fibers requires a better understanding of the behavior of polymer solutions in electrospinning to enable the design of more complex spinning dopes. In complex fluids, there are viscoelastic stresses and microstructural transitions that alter free surface flows. These may not be seen in shear rheology; therefore, an in-depth analysis of the extensional rheological behavior must be performed. In this work, we use dripping-onto-substrate rheometry to characterize the extensional viscosities of electrospinning dopes from four polymer solutions commonly used in electrospinning (low- and high-molecular-weight polyvinylpyrrolidone in methanol and water as well as poly­(ethylene oxide) and poly­(vinyl alcohol) in water). We link the electrospinnability, characterized through fiber morphology, to the extensional rheological properties for semidilute and entangled polymer solutions and show that high-surface-tension solvents require higher extensional viscosities and relaxation times to form smooth fibers and that the Deborah and Ohnesorge numbers are a promising method of determining electrospinnability. Through this tie between solvent characteristics, viscoelasticity, and electrospinnability, we will enable the design of more complex spinning dopes amenable to applications in wearable electronics, pharmaceuticals, and more.

Temperature-controlled dripping-onto-substrate (DoS) extensional rheometry of polymer micelle solutions

“…Most recently, Van Aeken et al 30 constructed a CaBER-based instrument with a brass fluid bath to enable horizontal extensional measurements in an external fluid; to conduct measurements at elevated temperatures, the brass frame can be heated via cartridge heaters. In contrast, in DoS instrumentation introduced by Dinic et al 16 and used by many others, [31][32][33][34] the sample is exposed to the environment and lacks heating elements. Thus, temperature-controlled extensional measurements are commonly accessible using CaBER instrumentation, but no developments to-date have been made towards temperature-controlled DoS measurements.…”

Evaporation-controlled dripping-onto-substrate (DoS) extensional rheology of viscoelastic polymer solutions

“…The evaporation-controlled DoS methodology presents the first environment to control evaporation in dripping-onto-substrate extensional rheology measurements of low-viscosity, volatile fluids. Aside from employing an oil bath 33 , suitable only for immiscible samples, or a chamber without a reservoir to generate an enriched solvent atmosphere 42 , 45 , capillary thinning extensional rheology measurements of volatile systems typically rely on reducing measurement time to reduce evaporation 5 , 40 , 41 . Thus the severity of evaporation effects cannot be easily quantified, due to the short timescale on which they occur 45 .…”

“…While most DoS experiments to-date focus on aqueous systems, recent work demonstrates use of the DoS technique to measure complex fluids in solvents with moderate boiling points ( C) like methyl ethyl ketone 5 , methanol 40 , and ethyl acetate 41 . These studies attempted to limit evaporation by performing trials quickly to minimize the time that the sample contacts the air.…”

Ultrasound-assisted air-jet spinning of silk fibroin-soy protein nanofiber composite biomaterials

“…Finally, the soybean protein/silk fibroin composite nanofiber membrane was obtained. The theory behind solution-jet spinning nanofibers involves the high-speed stretching principle of airflow and Bernoulli's principle [25] . When the high-pressure airflow leaves the outer nozzle, the pressure decreases, the energy of the jet increases, and the velocity of the gas increases, which in turn promotes the pressure drop in the center of the jet.…”

“…This forms a driving force that leads to an acceleration of the polymer solution. The high-velocity gas flow also generates shear forces at the gas/solution interface, which deforms the polymer solution from a droplet to a conical shape [25] . When this shear force overcomes the surface tension of the polymer solution, a solution jet is generated.…”