Efficient coalescence of two spreading drops

两个扩散液滴的有效聚结

• 批准号: RGPIN-2015-06542
• 负责人: Waghmare, Prashant
• 金额: $ 1.6万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=614207
• 关键词: Efficient; coalescence; two; spreading; drops

Liquid drop coalescence is a ‘mass transfer’ process between two miscible liquid drops after being brought in the vicinity of each other. This can be observed in both natural (rain drops and condensation of dew) and artificially engineered processes (film growth, inkjet printing, spraying, etc.). Controlled drop coalescence of simultaneously spreading drops is a crucial aspect for a number of applications as mentioned above. Coalescence dynamics in such applications dictates the efficient mass transfer between two spreading drops, and inefficient coalescence of spreading drops may result in several undesirable effects such as longer printing time, overuse of printing ink and wastage and spillage of environmentally hazardous liquids (up to ~50%) during spraying of pesticides or de-icing of planes. In order to significantly reduce such losses, in this research program the precise way to control the drop coalescence on the substrate is provided. The specific aim of the given research program is to propose the pathway for efficient coalescence which will ultimately eliminate undesirable effects occurring due to unaccounted forces. This will be obtained by investigating the role of inherent attractive-repulsive forces that have been neglected so far, particularly pertaining to the coalescence dynamics. During the process of drop spreading, two distinct length scales (macro and microscopic) can be observed — capillary length scale and molecular scale. The drops with a very small equilibrium contact angle coalesce through the precursor film. Generally, the precursor film is of a few nanometers and at this scale the attractive-repulsive forces may change the coalescence dynamics. Therefore, attractive-repulsive forces need to be considered during drop coalescence. Thus, in this proposed research, the impact of attractive-repulsive forces (molecular and microscopic phenomena) on the macroscopic nature of drop coalescence will be studied in detail.  It is expected that this program will provide a defined way to control drop coalescence on the substrate and it we will also fill the gaps in the current literature, particularly it will provide an explanation to several unexplained non-intuitive and uncommon phenomena - delayed coalescence, one drop chasing another drop before coalescence, longer delay-relaxation time before coalescence, and self-augmented oscillation during the coalescence, etc. This optimum and precise way of coalescence will be a paradigm shift in several industrial processes such as spray coating, inkjet printing, spraying of pesticides and de-icing of airplanes etc., which will significantly reduce the use of toxic and environmentally hazardous liquids.

液滴聚结是两个可混相液滴相互靠近后的“传质”过程。这可以在自然（雨滴和露水的凝结）和人工工程过程（薄膜生长，喷墨印刷，喷涂等）中观察到。如前所述，控制同时扩散液滴的液滴聚并是许多应用的关键方面。在这些应用中，聚结动力学决定了两个涂胶滴之间的有效传质，而涂胶滴的低效聚结可能会导致一些不良影响，如打印时间更长、油墨过度使用以及喷洒农药或飞机除冰期间环境有害液体的浪费和溢出（高达50%）。为了显著减少这种损失，本研究方案提供了控制基板上滴聚结的精确方法。