Reproducible ejection of highly-viscos liquid jets

We have developed a device to eject a highly-viscos liquid of 300-1,000 cSt as a focused jet using an impulsive force (Onuki et al. Phys. Rev. Applied 2018). However, variations in shape and area of the coated droplets were observed during periodic ejection of jets. Therefore, this study aims to elucidate the factors of the instability during periodic jetting and to improve the quality of coating. For that, we experimentally observed the jet behavior during periodic jetting. It is observed that the meniscus position and the shape of the meniscus changes with each ejection. Since the rise of the meniscus position can change the gradient of pressure impulse, which causes the acceleration of the fluid, and the meniscus shape can affect flow-focusing effect, these changes were found to cause variations in jet behavior at each ejection. A circulating refilling system was introduced in place of the conventional tank refilling system. Remarkably, reproducible ejection was achieved for more than 20 minutes. Also, the coating quality are considerably improved than that with the tank system. These results will facilitate the practical use of three-dimensional coating technology of high viscosity-liquids.