Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700, USA.
Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA.
J Colloid Interface Sci. 2019 Nov 1;555:498-508. doi: 10.1016/j.jcis.2019.07.075. Epub 2019 Jul 26.
While soil water repellency causes a variety of undesirable environmental effects, the underlying mechanism is unknown. We investigate the coupled effects of chemical characteristics and surface topology in a simple model system of two lipids, DSPE (1,2-distearoyl-sn-glycero-3-phosphoethanolamine) and DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine), and a clay substrate. These closely-related lipids allowed the study of how a small change in chemical structure influences the surface hydrophobicity.
Techniques ranging from molecular (simulations) to nanoscopic (atomic force microscopy) to microscopic (fluorescence microscopy) to macroscopic (contact angle measurements) were used to explore interactions at all length scales. The wettability was assessed from initial contact angle and time-dependent changes in droplet shape.
The lipid distribution depended on the lipid's melting temperature: solid lipids did not spread evenly through the film, while liquid ones did. However, the initial contact angle did not change appreciably with the addition of DSPE or DOPE. Only DSPE heated above its melting temperature induced significant changes. In addition to the initial contact angle, quantitative variables extracted from the change in droplet shape over time correlated with the film topography or lipid distribution. These results define a new quantitative approach to investigating partially-wettable soils and provide a potential rationale for why clays can remediate water-repellent soils.
尽管土壤抗水性会产生各种不良的环境影响，但其中的根本机制尚不清楚。我们在 DSPE（1,2-二硬脂酰-sn-甘油-3-磷酸乙醇胺）和 DOPE（1,2-二油酰基-sn-甘油-3-磷酸乙醇胺）这两种脂质与粘土基质组成的简单模型体系中，研究了化学特性和表面拓扑结构的耦合效应。这些密切相关的脂质可以帮助我们研究化学结构的微小变化如何影响表面疏水性。
我们使用了从分子（模拟）到纳米级（原子力显微镜）到微观（荧光显微镜）到宏观（接触角测量）等一系列技术，探索了所有长度尺度上的相互作用。通过初始接触角和液滴形状随时间的变化来评估润湿性。
脂质的分布取决于其熔点：固体脂质不会均匀地分布在薄膜中，而液体脂质则会。然而，添加 DSPE 或 DOPE 并不会显著改变初始接触角。只有加热到高于其熔点的 DSPE 才会引起明显变化。除了初始接触角外，从液滴形状随时间的变化中提取的定量变量与薄膜形貌或脂质分布相关。这些结果定义了一种新的定量方法，用于研究部分润湿土壤，并为为什么粘土可以修复抗水土壤提供了潜在的原理。
