We study the influence of variations of cross-section on the drying dynamics by pervaporation in microfluidic channels surrounded by water-permeable polydimethylsiloxane (PDMS) walls. Single channels of linearly increasing and decreasing width display similar drying time, but different dynamics towards final drying. Single channels with stepwise increasing or decreasing width show jumps of the drying velocity when the meniscus separating the water-filled and the dry part of the channel crosses the steps. In branched networks, narrower branches tend to dry faster than wider ones. All these observations are rationalised in the framework of a model based on the solution of the diffusion equation of water through PDMS, accounting precisely for the local channel geometry, provided the section variation is slow. This model shows that drying velocity depends strongly on the local channel width at the meniscus location. It captures quantitatively our measurements, except the magnitude of the velocity jumps in channels with steps. Implications and perspectives of this study are discussed in the context of leaf drying by the so-called air seeding mechanism in trees.

我们研究了横截面变化对由透水聚二甲基硅氧烷 (PDMS) 壁包围的微流体通道中的渗透蒸发的干燥动力学的影响。线性增加和减少宽度的单个通道显示相似的干燥时间，但对最终干燥的动态不同。当分隔充水部分和干燥部分的弯液面穿过台阶时，具有逐步增加或减小宽度的单个通道显示干燥速度的跳跃。在分支网络中，较窄的分支往往比较宽的分支干得更快。所有这些观察结果都在基于水通过 PDMS 的扩散方程的解的模型框架中进行了合理化，精确地考虑了局部通道几何形状，前提是截面变化很慢。该模型表明，干燥速度很大程度上取决于弯液面位置的局部通道宽度。它定量地捕获了我们的测量结果，除了通道中速度跳跃的幅度有台阶。本研究的意义和前景在树叶干燥的背景下通过所谓的树木空气播种机制进行了讨论。