Nikolov Alex, Murad Sohail, Wasan Darsh, Wu Pingkeng
Department of Chemical and Biological Engineering Illinois Institute of Technology, Chicago, IL, 60616, USA.
J Colloid Interface Sci. 2020 Oct 15;578:660-667. doi: 10.1016/j.jcis.2020.04.123. Epub 2020 Jun 2.
As kids, the authors enjoyed learning how to write by dipping nib pens into ink, and then later, using flex nib pens for calligraphy. They remember, less fondly, the troubles with ink leaks and spills over the paper's surface. Despite advances in fountain pen design, the performance of fountain pens is still not perfect. A robust fountain pen has to provide a sustainable ink flow-no leaks-for smooth and precise writing on paper. In the long history of the design and development of fountain pens, more attention has been focused on the ink flow than on the ink/air capillary flow balance. It is found that as ink flows out of the cartridge, the holding pressure in the ink cartridge builds up and the pressure drop across the capillary valve increases. Consequently, the air is sucked toward the ink cartridge. An air-ink meniscus is formed at the capillary valve and finally breaks into air bubbles due to Rayleigh instability. The air bubbles float into the ink cartridge under buoyancy force to reduce the holding pressure so that the ink can continuous flow out to the nib to keep the fountain pen in function. The unbalance between the air holding pressure in the ink cartridge and the pressure drop across the capillary valve is the key for the functionality of the fountain pen. A poor design of the feed/cartridge connection with a small orifice of the capillary valve leads to the malfunction of the fountain pen.
小时候，作者们喜欢通过将笔尖蘸入墨水中来学习写字，后来又使用弹性笔尖钢笔进行书法练习。他们不太愉快地记得墨水泄漏和溅到纸张表面的麻烦。尽管钢笔设计有了进步，但钢笔的性能仍然不尽完美。一支坚固的钢笔必须提供可持续的墨水流动——不泄漏——以便在纸上流畅、精确地书写。在钢笔设计和开发的漫长历史中，更多的注意力集中在墨水流动上，而不是墨水/空气毛细管流动平衡上。研究发现，当墨水从墨盒流出时，墨盒中的保持压力会增加，毛细管阀两端的压降也会增加。因此，空气被吸向墨盒。在毛细管阀处形成气-墨弯月面，最终由于瑞利不稳定性而破裂成气泡。气泡在浮力作用下浮入墨盒以降低保持压力，从而使墨水能够持续流出到笔尖，使钢笔正常工作。墨盒中的空气保持压力与毛细管阀两端的压降之间的不平衡是钢笔功能的关键。进料/墨盒连接设计不佳，毛细管阀的小孔径会导致钢笔出现故障。
