Z. Li, D.R. Chen, H. Zhao
Virginia Commonwealth University,
Keywords: electrohydrodynamic printing, dual-channel nozzle, ink circulation, meniscus shape
Summary:EHD printing has attracted extensive research interests and it has been successfully used for the fabrication of micro-/nano-structures including applications such as microelectronics, pharmaceutics, and fabrication of functional materials. Fine nozzles with inner diameters of several micrometers were often utilized to generate high-resolution patterns/features by the single-capillary EHD printing. As the nozzle size scales down, it is inevitable to encounter severe nozzle clogging due to solvent evaporation and ink accumulation at the nozzle tip, which has hindered its acceptance as a viable manufacturing approach. A novel dual-channel nozzle design has been proposed to mitigate the nozzle clogging by introducing a continuous ink circulation. This dual-channel nozzle consists of two co-axially aligned capillaries, forming the inner and outer channel. Continuous ink circulation has been demonstrated between the inner and outer channel, and various EHD jetting modes have been identified. Continuing this work, we have studied the effect of the meniscus pinning on the jetting characteristics of this unique dual-channel EHD printing. Depending on the extension length of the inner channel out of the outer channel, the shape and pinning location of the meniscus vary. Specifically, at a short extension length, a large meniscus forms and pins at the outer channel. In this case, a large electric field is required to initiate the jetting formation. As a result, large droplets are generated from the apex of the meniscus. As the inner channel sticks more out of the outer channel, the meniscus volume reduces significantly, and new pinning occurs at the inner channel. The applied electric field only actuates the micro meniscus pinned at the inner channel, while the meniscus or “bridge” between the inner and outer channel remains stable with a continuous ink circulation. This significantly reduces the droplet size (~5-10 times). When further increasing the extension length, the meniscus between the inner and outer channel may break and the ink circulation is interrupted. Furthermore, we also study the effect of channel size, ink properties, and applied electric field on the meniscus dynamics and jetting behavior, which ultimately affects the printed dot size and resolution. This study will lead to the development of a novel EHD jet printing technique without the primary technical barriers (e.g. nozzle clogging) and pave the way for using EHD printing as a scalable manufacturing platform.