High-Speed Observations of Acoustic Droplet Ejection of a Shear-Thinning Polymer Solution in an External High-Voltage Electric Field

High-speed observations of ultrasonic ejection of a viscoelastic, shear-thinning, polymer solution, 1 wt% PEO dissolved in water, for the purpose of electrospinning initiation are presented. A focused ultrasound source at 2.68 MHz is used for the ejection. A high-voltage electric field is applied between the solution and a conducting plate above. With a suitable ultrasonic ejection of the solution, electrospinning is initiatied as the electric field pulls a thinning jet from the solution, eventually producing a nanofiber.Two ultrasonic pulse regimes are investigated for the ejection: short (≤ 100 cycles) but high-amplitude (≈ 4.4 MPa), and long (≥ 5000 cycles) but low-amplitude (≈ 0.8 MPa) pulsing. Three different types of ejections leading to the electric field being able to pull a jet from the solution are observed. Most notably, we observed an unstable drop-chain formation which lead to the jetting of liquid from the drop-chain, which was further pulled by the electric field into a thinning jet.