Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacyo, Koganei, Tokyo, 184-8588, Japan.
Soft Matter. 2017 Oct 11;13(39):7026-7033. doi: 10.1039/c7sm01490b.
Herein, we report assessments of the kinetics in directional drying of water that contains non-volatile oil droplets, based on direct observations using a confocal microscope. The water was found to evaporate at a constant rate during the initial stage of drying, after which the evaporation rate decreased. The dispersed oil droplets were compressed and distorted as the surrounding water was lost. Further evaporation of water resulted in coalescence of the oil droplets, with the eventual formation of an oil layer at the drying interface. However, it was apparent that the drying rate decreased even before the formation of this oil layer. We propose that the restricted transport of water via the narrow paths between the distorted oil droplets was responsible for the decreased drying rate. A mathematical model based on foam drainage theory is proposed and describes the experimental data very well. This work also determined that the critical disjoining pressure for the oil droplets is affected by the drying rate, such that higher pressure values are associated with slow drying conditions. The drying kinetics and stability of the dispersed oil droplets are discussed.
本文通过使用共聚焦显微镜进行直接观察，报告了对含有非挥发性油滴的水进行定向干燥的动力学评估。研究发现，在干燥的初始阶段，水以恒定的速率蒸发，之后蒸发速率降低。随着周围水分的流失，分散的油滴被压缩和变形。进一步的水分蒸发导致油滴聚结，最终在干燥界面形成一层油。然而，显然在形成这个油层之前，干燥速率就已经降低了。我们提出，由于扭曲油滴之间的狭窄路径限制了水的传输，导致干燥速率降低。提出了一个基于泡沫排水理论的数学模型，很好地描述了实验数据。这项工作还确定了油滴的临界分离压力受干燥速率的影响，即较高的压力值与缓慢的干燥条件相关。讨论了分散油滴的干燥动力学和稳定性。
