Journal
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume 555, Issue -, Pages 498-508Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2019.07.075
Keywords
Soil water repellency; Soil organic matter; Clay; Molecular dynamics; Nanotopology
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Funding
- National Science Foundation Graduate Research Fellowship Program [DGE-1762114]
- US Department of Energy (DOE), Office of Basic Energy Sciences (BES) Chemical Sciences, Geosciences, and Bio-sciences Division at Pacific Northwest National Laboratory (PNNL)
- DOE [DE-AC05-76RL01830]
- National Science Foundation [NNCI-1542101]
- University of Washington
- Molecular Engineering & Sciences Institute
- Clean Energy Institute
- National Institutes of Health
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Hypothesis: 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. Experiments: 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. Findings: 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. (C) 2019 Elsevier Inc. All rights reserved.
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