Soil water repellency, that is, the reduced ability of soils to absorb water, is thought to be caused by organic coatings with predominantly non‐polar properties on soil particle surfaces. Given the important role of particle surface polarity in determining soil water repellency, we explored the use of fluorescent probes as a method for the direct in‐situ determination of the distribution and polarity of organics on bulk soil surfaces, and of their molecular mobility. We used nile red and pyrene, which have both been used successfully as environmental probes in previous studies, but have not been applied before to bulk soils. The probes were either (a) co‐deposited with other organics known to induce water‐repellent behaviour with acid‐washed sand to produce ‘model soils’ or (b) adsorbed directly onto sandy soils that were naturally water repellent to different degrees, and studied using fluorescence microscopy and steady‐state and time‐resolved fluorescence. Reliable measurements could be made using pyrene as an in‐situ probe on both model and natural soils, and a viscosity/mobility probe on model soils, whereas nile red was found not to be a useful probe. On model soils, made using hexadecane (HEX), octadecane (OCT) or stearic acid (SA) on acid‐washed sand, pyrene excimer formation kinetics showed a decrease in environment mobility as the organic layer changes from a liquid through to a hard wax. Spectra from pyrene adsorbed to natural soils indicated varying environmental polarity and heterogeneity within the soil samples studied.

中文翻译：

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yr和尼罗红荧光探针用于土壤有机涂层极性和粘度的原位研究，涉及土壤疏水性

土壤憎水性，即土壤吸收水的能力下降，被认为是由土壤颗粒表面主要具有非极性性质的有机涂层引起的。鉴于颗粒表面极性在确定土壤疏水性中的重要作用，我们探索了使用荧光探针作为直接原位检测的方法测定散装土壤表面上有机物的分布和极性及其分子迁移率。我们使用了尼罗红和pyr，它们在先前的研究中均已成功用作环境探针，但之前并未用于散装土壤。探头要么（a）与其他已知会与酸洗过的沙子产生拒水行为的有机物共同沉积，以产生“模型土壤”，要么（b）直接吸附到天然具有不同程度拒水程度的沙土上，并且使用荧光显微镜以及稳态和时间分辨荧光进行了研究。可以使用pyr作为原位进行可靠的测量在模型土壤和天然土壤上都可以使用探针，而在模型土壤上可以使用粘度/迁移率探针，而尼罗河红不是有效的探针。在酸洗过的沙子上使用十六烷（HEX），十八烷（OCT）或硬脂酸（SA）制成的模型土壤上，pyr准分子的形成动力学表明环境迁移率降低，因为有机层从液态变为硬蜡。pyr吸附到天然土壤上的光谱表明，所研究土壤样品中的环境极性和异质性各不相同。