Cedeno Ruel, Grossier Romain, Tishkova Victoria, Candoni Nadine, Flood Adrian E, Veesler Stéphane
CNRS, Aix-Marseille University, CINaM (Centre Interdisciplinaire de Nanosciences de Marseille), Campus de Luminy, Case 913, F-13288 Marseille Cedex 09, France.
Department of Chemical and Biomolecular Engineering, School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology, Rayong 21210, Thailand.
Langmuir. 2022 Aug 9;38(31):9686-9696. doi: 10.1021/acs.langmuir.2c01269. Epub 2022 Jul 28.
The occurrence of concentration and temperature gradients in saline microdroplets evaporating directly in air makes them unsuitable for nucleation studies where homogeneous composition is required. This can be addressed by immersing the droplet in oil under regulated humidity and reducing the volume to the picoliter range. However, the evaporation dynamics of such a system is not well understood. In this work, we present evaporation models applicable for arrays of sessile microdroplets with dissolved solute submerged in a thin layer of oil. Our model accounts for the variable diffusion distance due to the presence of the oil film separating the droplet and air, the variation of the solution density and water activity due to the evolving solute concentration, and the diffusive interaction between neighboring droplets. Our model shows excellent agreement with experimental data for both pure water and NaCl solution. With this model, we demonstrate that assuming a constant evaporation rate and neglecting the diffusive interactions can lead to severe inaccuracies in the measurement of droplet concentration, particularly during nucleation experiments. Given the significance of droplet evaporation in a wide array of scientific and industrial applications, the models and insights presented herein would be of great value to many fields of interest.
盐微滴在空气中直接蒸发时会出现浓度和温度梯度，这使得它们不适用于需要均匀成分的成核研究。可以通过将液滴置于湿度可控的油中，并将体积减小到皮升范围来解决这个问题。然而，这样一个系统的蒸发动力学还没有得到很好的理解。在这项工作中，我们提出了适用于浸没在薄油层中且含有溶解溶质的无柄微滴阵列的蒸发模型。我们的模型考虑了由于油膜分隔液滴和空气而导致的可变扩散距离、由于溶质浓度变化而引起的溶液密度和水活度的变化，以及相邻液滴之间的扩散相互作用。我们的模型与纯水和氯化钠溶液的实验数据都显示出极好的一致性。利用这个模型，我们证明，假设蒸发速率恒定并忽略扩散相互作用会导致在液滴浓度测量中出现严重误差，特别是在成核实验期间。鉴于液滴蒸发在众多科学和工业应用中的重要性，本文提出的模型和见解将对许多感兴趣的领域具有巨大价值。
