Electrohydrodynamic Deposition of Polymeric Droplets under Low-Frequency Pulsation

Circularly shaped polymeric droplets with diameter of about 20 μm have been intermittently ejected and deposited in an orderly manner on a collector from a syringe needle by means of near-field, electrohydrodynamic reactions using pulsating voltages at around 2.25 kV. The needle has an inner diameter of 100 μm and was placed 1 mm above a silicon conductor substrate to have location control for droplet depositions. Under low-frequency operation of less than 100 Hz, the deposition frequency of droplets, <i>f</i><sub>dep</sub>, has been observed to be equal to the frequency of the applied driving voltage divided by an integer, <i>N</i>, as small as 1. Furthermore, the diameter of the deposited droplets has been found to be linearly dependent on (<i>Q</i>/<i>f</i><sub>dep</sub>)<sup>1/3</sup>, where <i>Q</i> is the polymer solution supply rate at around 30 nL/s. These experimentally observed droplet ejection rules under low-frequency pulsation provide useful design guidelines for controllable deposition of polymer droplets in various potential applications, including electrohydrodynamic printing.