Abstract
Electrospinning is a widely used production method for nanoscale fine polymer fiber fabrics. An ultrafine fiber made of polymers such as polyvinylpyrrolidone (PVP) polyacrylic acid (PAA) has immense potential for applications in air filters, batteries, and biosensors. However, producing fabrics with long uniformly distributed ultrafine fibers of a mean diameter below ~ 200 nm is still a challenge, because such elongated-ultrafine fibers tend to break into beads before they reach the collector. Here, we exploits the thixotropy of the solution given by the addition of 2,2,6,6-tetramethylpiperidin-1-oxyl-oxidized cellulose nanofibers to recover the solution viscosity for stabilizing the electrostatically elongated nanofibers, whereby the solution is smooth in the syringe needle owing to the shear force but regain its original viscosity after being freed from electrostatic force. Using this method, we successfully fabricated a non-woven ultrafine-long nanofiber made of PVP and PAA with a mean diameter as low as ~ 90 nm with a negligible number of beads.
Highlights
Electrospinning is a widely used production method for nanoscale fine polymer fiber fabrics
The solution exhibited a conductivity of 47 mS m−1, which was more conductive than the 0.4 wt.% TEMPO-cellulose nanofibers (CNF)-added 12 wt.% PVP aqueous solution and we see improvements in average fiber diameter and fiber ratio, the fiber ratio did not significantly increase to the degree that TEMPO-CNF containing solution exhibited (Supplementary Fig. 4), proving that the small charge introduced by CNF does not decrease the number of beads, and the increased fiber ratio was solely attributed to the viscosity recovery during electrospinning
We confirmed the thixotropic behavior of the solutions and ascribed it to the dynamic viscosity tuning (DVT) stabilizing the produced elongated nanofiber before beads started to form after leaving the syringe needle and being freed from the large tensile stress owing to the surface charge, which repels the neighboring segments of the polymer in nanofiber and decreases the fiber diameter (Fig. 1d)
Summary
Electrospinning is a widely used production method for nanoscale fine polymer fiber fabrics. We exploits the thixotropy of the solution given by the addition of 2,2,6,6-tetramethylpiperidin-1oxyl-oxidized cellulose nanofibers to recover the solution viscosity for stabilizing the electrostatically elongated nanofibers, whereby the solution is smooth in the syringe needle owing to the shear force but regain its original viscosity after being freed from electrostatic force Using this method, we successfully fabricated a non-woven ultrafine-long nanofiber made of PVP and PAA with a mean diameter as low as ~ 90 nm with a negligible number of beads. For needle electrospinning, the primary parameters affecting the final structure of the electrospun non-woven textile are the viscosity, dielectric constant, surface tension of the solution, solution feed rate, and bias voltage applied to the polymer solution between the syringe and collector, all of which determine the constituting fiber diameter and m orphology[11,12] These parameters are essential even for the state-of-the-art electrospinning method, and conditions for fabricating textiles with uniform fine polymer fibers have been widely investigated. Viscosity recovery Low stress in this elongated state, are highly sought after to prevent breakage into beads before the fiber reaches the winder or fiber collector
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