Evaporation and Rheology Chart the Processability Map for Centrifugal Force Spinning

Abstract

We show that poly­(ethylene oxide) (PEO) solutions formulated using solvent mixtures of acetonitrile (AcN) and water can be centrifugally spun into fibers. We find that spinnability and fiber morphology depend on solvent choice if polymer concentration, solution shear rheology, the number of entanglements, extensional relaxation time, and the parameters for centrifugal spinning are nearly matched. We obtain an intrinsic spinnability map for volatile entangled (VE) polymer solutions by contrasting the measured shear relaxation time with the evaporation rate determined using thermogravimetric analysis (TGA). Finally, we chart a processability map for centrifugal spinning by plotting extensional relaxation time, measured for the volatile polymer solutions using a closed-cell dripping-onto-substrate (DoS) rheometry, against the time of flight (from the nozzle to the collector) by scaling both the timescales with an evaporation time. The processability map incorporates the influence of centrifugal spinning speed, nozzle diameter, distance from the collector, ambient conditions, and solvent and polymer properties, establishing an imitable paradigm for distinguishing between spinnable and sprayable formulations.

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

“…As the DoS technique was pioneered less than one decade ago, one major limitation is that DoS measurements are limited to ambient temperatures. Recently, researchers have created closed chambers 28 or chambers with solvent reservoirs 23 to enable DoS measurements in volatile solvents. However, a temperature control chamber has yet to be incorporated into DoS rheometry, whereas heated CaBER has been developed both commercially and via custom design.…”

Nozzle‐Pressurized Gyration: A Novel Fiber Manufacturing Process

“…Different from PCL and PVP fibers, increasing collection distance produced better PEO nanofibers with unidirectional arrangement in nozzle‐PG, since it is more difficult for pure water to fully evaporate compared with organic solvents. [ 68 ] The spinning jets experience air resistance when travelling in air, during which the solvent undergoes forced convective mass transfer on the jet surface. [ 69 ] Subsequently, the solvent evaporates to form dry fibers.…”

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 .…”

“…These studies attempted to limit evaporation by performing trials quickly to minimize the time that the sample contacts the air. Recent work by Merchiers and coworkers used a sealed environment to slow evaporation in acetonitrile/water solutions, albeit without a solvent reservoir to saturate the environment 42 . However, none of these works quantified or estimated evaporation effects on the pendant drop.…”

“…As the evaporation rate is a central consideration in selecting processing parameters for coating processes incorporating volatile solvents 43 , 44 , these volatile coatings can only be studied by controlling evaporation to the environment. Furthermore, without a method of true environmental control, the effect of evaporation on extension cannot be easily separated from the effect of flow rate 5 , 41 or of solvent quality 42 . Currently, evaporation effects are best studied by repeating trials at varying exposure times, similar to work by Tripathi and McKinley on hygroscopic glycerol solutions 45 .…”