Connections between Macroscopic Wettability and Lipid Structures on Clay Montmorillonite

Abstract

Soil organic matter, which includes lipids from bacterial membranes, influences characteristics of soil such as soil water repellency. However, the mechanism that governs the distribution of lipids on mineral surfaces and the consequent alteration of macroscale wettability is unclear. This project investigates phospholipid-clay films to understand how lipids influence wettability. Previous investigations conducted to study the physical characteristics of the lipid-mineral surfaces focused on phosphoethanolamine (PE) lipids on the clay mineral montmorillonite. In this study, the physical characteristics of phosphoglycerol (PG) lipids on montmorillonite were studied. As PE lipids are zwitterionic and PG lipids are negatively charged, these lipids interact with the clay surface differently and can be used to determine how lipid-clay interaction alters wettability. The physical characteristics of the lipid-mineral films were studied using atomic force microscopy and fluorescence microscopy. Atomic force microscopy experiments were conducted to study the topography of the PG-montmorillonite surfaces while fluorescence microscopy was employed to map the distribution of the lipids on the montmorillonite surface. Additionally, wettability experiments were conducted on the surface of the PG-montmorillonite samples to determine the kinetics of water soaking into the film. Physical characteristics were then compared to wettability data to establish causative relationships. We find that the small-scale distribution of lipid aggregates has the most impact on macroscopic wettability for PG lipids, whereas, for PE lipids, the lipid distribution across hundreds of microns was the main influence.