A simple and low-cost method is suggested to fabricate nanochannels via Near-Field Electrospinning (NFES). In this process, orderly and patterned nanofibers direct-written by NFES are used as sacrificial templates. Well-defined nanochannels are available after the removal process of both sacrificial fibers and material coating over the fibers. The sacrificial fiber, controlled by NFES, dominates the channel geometry. The channel width ranges from 133 nm to 13.54 mu m while the applied voltage increases from 1.2 kV to 2.5 kV. Complicated wave-shape and grid pattern channels are presented under a corresponding movement of substrate. This method integrates electrospinning with conventional MEMS fabrication technology and has a potential in micro/nano manufacturing.National Natural Science Foundation of China [51035002, 51105320]; Fundamental Research Funds for the Central Universities [2010121039

Pulsed electrohydrodynamic printing (EHDP) is used to fabricate conductive silver patterns with micrometer resolution. The silver ink pendant experiences swelling, pulsation, and ejection under an applied pulse voltage of 20 Hz. The droplet deposition frequency is equal to the applied voltage frequency so that the EHDP can deposit silver ink on demand. A low applied voltage favors uniform and non-scattering silver patterns while a high applied voltage results in ink scattering. Discrete droplets with 45-55 mu m in diameter and continuous tracks with 60 mu m in width are generated by using a 110-mu m-cailber nozzle. The feature size of deposited patterns is about half of the nozzle caliber, and a finer resolution can be achieved with the introduction of smaller nozzle calibers. Furthermore, the appropriate curing condition is investigated for sufficient combustion of ink solvent. The minimum resistivity of 3.3 mu Omega cm is demonstrated for a continuous track cured at 200 degrees C for 10 min. Eventually, several passive electrical components, such as coated resistors, interdigitated capacitors (6 pF), and spiral inductors (0.6 mu H), are successfully fabricated.National Natural Science Foundation of China [51035002]; Chinese Ministry of Education [708055]; Fundamental Research Funds for the Central Universities [2010121039

Gap electrospinning is a facile technique to produce aligned nanofibers useful for many applications, but its potential has not yet been fully exploited in nature, leading to the fiber length still limited to several tens of centimeters at present. In this work, we report a breakthrough in the production of well-aligned nanofibers with record length and efficiency. Using a suitable poly(vinylidene fluoride) solution and a pair of parallel plates that are substrate-free and negatively connected, we demonstrate the ease of this technique to prepare length-controllable aligned fibers in a wide range (≤125 cm). Because of the crucial roles of both the jet whipping instability that continuously drives the jet to span across the static plates and the negative voltage on the plates that effectively attracts the positively charged jet, the jet can be made to move back and forth over the superlarge gap to form ultralong aligned nanofibers. By introducing a projection method, we also redefine fiber alignment in a broader sense. This work is believed to provide a new insight into the nature of gap electrospinning, which will greatly expand the versatility of this technique to create devices for a myriad of applications.

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, f(dep), has been observed to be equal to the frequency of the applied driving voltage divided by an integer, N, as small as 1. Furthermore, the diameter of the deposited droplets has been found to be linearly dependent on (Q/f(dep))(1/3), where Q 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.

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A pole-type nozzle has an inserted pole that jams a contraction flow into capillary in electrohydrodynamic deposition. The jammed solution improves Taylor cone formation by shortening the hysteresis time so that pole-type nozzle is suitable for high-resolution electrohydrodynamic printing. Experimental results demonstrate a governed frequency-dividing relationship with an integral ratio of applied voltage frequency to droplet deposition frequency. It is observed that low integral frequency ratio is in favor of low voltage amplitude and duty cycle, and high voltage frequency, since polymer solution jets in a small fluidic volume per droplet under low electric force and short pulse duration. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775672