Inkjet printing as an additive fabrication method has been used in the manufacturing of printed electronics, 3-D object prototypes, solar cells, and light-emitting devices, as well as applications in tissue engineering and other biological and pharmaceutical fields. Unlike the more common method of piezo inkjet printing, which typically generates individual droplets of 10-50 micrometers in diameter, voltage-modulated electrohydrodynamic (EHD) jet printing has a demonstrated ability to produce sub-micrometer-sized droplets/fibers for the fabrication of patterns or features at nanometer scales. However, EHD jet printing has not been considered as a viable manufacturing tool because of the issues of nozzle clogging, ink accumulation at the nozzle exit, and low printing frequencies (resulting in a limited production rate). This project conducts fundamental research on a new form of EHD jet printing, using novel dual-channel printing nozzles and electrical current (instead of voltage) modulation. It is hypothesized that the circulation of liquid ink in the dual channels will eliminate nozzle clogging due to evaporation of carrier fluids or polymerization of ink, and the current modulation/control will enable high-speed, drop-on-demand EHD jet printing. This research could also lead to further improvements on current inkjet printing processes or devices in both industrial and household settings. Furthermore, the technique will be used in education and outreach activities geared toward students (at all levels) and workers in advanced manufacturing.
This project will investigate the fundamental science involved in a new current-modulated, drop-on-demand EHD printing method with novel dual-channel nozzles for the fabrication of high-resolution micro/nano patterns at high jetting frequencies (on the level of MHz). The proposed dual-channel printing nozzles use two concentric tubes, providing an annular channel around the inner tube. In the proposed nozzle configuration, one channel provides new ink and the other for extracts ink from the nozzle, thereby achieving fluid circulation within the dual tube nozzle. It is hypothesized that this fluid circulation will eliminate or greatly reduce the issues of nozzle clogging and ink accumulation associated with polymerization or carrier fluid evaporation at the nozzle outlet.  This project further hypothesizes that the ejection rate of droplets can be increased through current control, instead of the voltage control commonly used. Scientific understanding of fluid meniscus dynamics and droplet generation in the proposed EHD printing will be required to achieve robust current control, and needs to incorporate effects of fluid recirculaiton. The novelties of the proposed EHD jet printing technique are i) the proposed dual-channel nozzles that will resolve the technical issues often encountered in single-capillary inkjet printing; and ii) the modulation of frequencies with current rather than voltage in order to achieve reliable EHD jet printing at high jetting frequencies. The specific aims of this project are to: i) develop the fundamental science involved in liquid meniscus formation, jetting, and droplet ejection in a voltage-modulated EHD jet printing process with the dual-channel nozzles; ii) investigate the fundamental jetting mechanisms in current-modulated EHD jet printing process (particularly at high frequencies); iii) numerically model the jetting characteristics in the EHD jet printing technique to develop the underlying fundamental science and aide control strategies; and iv) provide a proof-of-concept of the proposed approach and validate the numerical models through parametric investigations of the quality (i.e. the size, uniformity, and resolution) of micro/nano-sized patterns created.
