Evolution of meniscus structures in hydrophobic granular systems
Evolution of meniscus structures in hydrophobic granular systems
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DOI：
10.1016/j.jhydrol.2021.126954
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发表时间：
2021-10
影响因子：
6.4
通讯作者：
Z. Karatza;J. Buckman;G. Medero;Christopher T. S. Beckett
中科院分区：
文献类型：
--
作者：
Z. Karatza;J. Buckman;G. Medero;Christopher T. S. Beckett
在干旱地区或森林火灾后自然形成的疏水性土壤可能会给土地管理者和工程师带来问题，因为它们通常与阻碍或优先流动路径、地表径流增加和土壤侵蚀有关。然而，防水土壤降低的雨水渗透能力也可以改善斜坡、垃圾填埋场和毛细管屏障覆盖系统等的稳定性。如果要解决稳定性和渗漏问题，了解这些材料内的水力条件至关重要。对不饱和疏水性土壤的传统理解表明，凸水弯月面和正水压应该在土壤颗粒之间形成。然而，文献中提出的有限实验结果并不支持这一理论。在这项工作中，在宏观（多个颗粒）和颗粒尺度上研究了颗粒形状对水弯月面结构的形成和演化的影响，对比了球形玻璃珠和有角砂粒之间的弯月面行为。在宏观尺度上检查了座滴的扩散，发现当沉积在单层颗粒上时，沙粒的棱角对座滴的表观接触角有显着影响。在颗粒尺度上，环境扫描电子显微镜用于研究毛细管桥的形成和演变以及两个润湿和干燥循环期间的保水滞后现象。再次表明，颗粒的形状和表面粗糙度是液桥形成和演变的控制因素，并且稳定的凸面和凹面弯月面可以在疏水颗粒表面之间同时共存。此外，研究发现，颗粒的疏水性使得弯月面形成的间隔距离比通过亲水表面之间的薄膜聚结所能达到的间隔距离大得多，这可能对渗透和吸入建模产生影响，更广泛地说，对依赖疏水性基材的制造过程产生影响。最后，疏水性土壤总体上表现出比亲水性土壤更小的保水曲线滞后。
Hydrophobic soils, which form naturally in arid regions or after forest fires, can be problematic for land managers and engineers as they are often associated with impeded or preferential flow paths, increased surface runoff and soil erosion. However, the reduced rainwater infiltration capacity of water-repellent soils can also result in the improvement of the stability of slopes, landfills and capillary barrier cover systems, amongst others. Understanding the hydraulic conditions within these materials is critical if issues of stability and seepage are to become tractable.Traditional understanding of unsaturated hydrophobic soils suggests that convex water menisci, and so positive water pressures, should form between soil particles. However, the limited experimental results presented in the literature do not support this theory. In this work, the effect of particle shape on the formation and evolution of water meniscus structures is investigated at the macro (multiple particles) and particle scales, contrasting meniscus behaviours between spherical glass beads and angular sand grains. The spreading of a sessile drop in the macro-scale is examined and found that the angularity of the sand grains has a significant effect on the apparent contact angle of a sessile drop when deposited on a mono-layer of particles. At the particle scale, Environmental Scanning Electron Microscopy was used to investigate the formation and evolution of capillary bridges and the water retention hysteresis during two wetting and drying cycles. Again, it is shown that the shape and surface roughness of the particles are controlling factors in both the formation and evolution of liquid bridges and that stable convex and concave menisci can co-exist simultaneously between hydrophobic particle surfaces. Additionally, it was found that the hydrophobic nature of the particles allowed menisci to form across much larger separation distances than could be achieved through film coalescence between hydrophilic surfaces, with possible consequences for infiltration and imbibition modelling and, more broadly, manufacturing processes relying on hydrophobic substrates. Lastly, the hydrophobic soils qualitatively exhibited overall much less hysteresis of the water retention curve than their hydrophilic counterparts.