Connecting wettability, topography, and chemistry in a simple lipid-montmorillonite system

Brenda L Kessenich; Nihit Pokhrel; Elias Nakouzi; Christina J Newcomb; Markus Flury; Lutz Maibaum; James J De Yoreo

doi:10.1016/j.jcis.2019.07.075

Connecting wettability, topography, and chemistry in a simple lipid-montmorillonite system

J Colloid Interface Sci. 2019 Nov 1:555:498-508. doi: 10.1016/j.jcis.2019.07.075. Epub 2019 Jul 26.

Authors

Brenda L Kessenich¹, Nihit Pokhrel¹, Elias Nakouzi², Christina J Newcomb², Markus Flury³, Lutz Maibaum¹, James J De Yoreo⁴

Affiliations

¹ Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700, USA.
² Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA.
³ Department of Crop and Soil Sciences, Washington State University, Pullman, WA 99164, USA; Department of Crop and Soil Sciences, Washington State University, Puyallup, WA 98371, USA.
⁴ Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA; Materials Science and Engineering, University of Washington, 302 Roberts Hall, Box 352120, Seattle, WA 98195-2120, USA. Electronic address: james.deyoreo@pnnl.gov.

PMID: 31401482
DOI: 10.1016/j.jcis.2019.07.075

Abstract

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.

Keywords: Clay; Molecular dynamics; Nanotopology; Soil organic matter; Soil water repellency.