Recent studies have indicated that under certain conditions, most soils are water repellent to some degree, which impacts agricultural fields, pastures, forests, grasslands, and turf areas. Soil water repellency originates from amphiphilic molecules that reorient during contact with water. However, models to describe the flow in soils affected by time‐dependent contact angle (CA(t)) are still lacking. The current study aims to close this gap. The measured CA(t) for an oleic acid‐coated glass surface and a uniform capillary tube indicated that the initial CA was substantially higher for the latter. However, the rate of CA decrease was similar for both cases in spite of the fact that the contact area between the water and the tube wall continuously increases by the capillary rise. This indicates that the amphiphilic molecules reorientation at the vicinity of the contact line rather than at the wetted tube area controls the CA dynamics. A mathematical model for flow in a uniform and sinusoidal capillary tube with CA(t) < 90° that includes model for the reorientation of the amphiphilic molecules was introduced. The model for uniform case was successfully verified by comparison with measured capillary rise in a coated uniform tube. The simulations indicated that nonuniform pore geometry amplifies the effect of CA(t) on the capillary rise dynamics. The stepwise meniscus propagation in the sinusoidal capillary tubes is driven by the time for the meniscus to reach the converging section of the tube. The retardation in capillary rise increases with tube waviness.

中文翻译：

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时变接触角对亚临界憎水土壤润湿性的影响

最近的研究表明，在某些条件下，大多数土壤在某种程度上具有憎水性，这会影响农田，牧场，森林，草地和草皮地区。土壤疏水性源自与水接触时会重新定向的两亲分子。但是，仍然缺乏描述受时间依赖性接触角（CA（t））影响的土壤中水流的模型。当前的研究旨在缩小这一差距。对油酸涂层的玻璃表面和均匀的毛细管测得的CA（t）表明，后者的初始CA值要高得多。但是，尽管水和管壁之间的接触面积因毛细管的上升而连续增加，但两种情况下的CA降低率均相似。这表明在接触线附近而不是在湿管区域的两亲分子重新取向控制了CA动力学。引入了一个在CA（t）<90°的均匀正弦毛细管中流动的数学模型，其中包括两亲分子的重新定向模型。通过与带涂层的均匀管中测得的毛细管上升进行比较，成功验证了均匀情况模型。模拟表明，不均匀的孔几何形状会放大CA（t）对毛细管上升动力学的影响。在弯月形毛细管中逐步的弯月面传播是由弯月面到达管的会聚部分的时间驱动的。毛细管上升的延迟随管的波纹度而增加。