Electron and Force Microscopy Characterization of Particle Size Effects and Surface Phenomena Associated with Individual Natural Organic Matter Fractions

Abstract

AbstractNatural organic matter (NOM) generically refers to organic substances found in soils, waters, and sediments. It is the brown-to-black, heterogeneous organic material produced through the diagenetic alteration of plant tissue and microbial biomass via a myriad of biotic and abiotic reactions. Since NOM is the primary source of organic carbon in the earth’s surficial environment, understanding the processes by which NOM is produced is integral to understanding carbon sequestration, contaminant fate and transport, and other earth surface processes. NOM samples (HA0) consist of nonamphiphilic (HA1), lipid-like (L0 and L1), and strongly amphiphilic (HA2) components. Here we present the structure and morphology of self-assembled NOM components based on scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrostatic force microscopy (EFM) characterizations. Effects of surface charge and hydrophobicity/hydrophilicity of the amphiphile on the interaction and resulting structures were investigated using SEM, AFM, and EFM. Data shows that the component’s amphiphilic nature plays a key role in the formation of NOM. SEM data show that aggregates form while AFM/EFM analysis verifies the existence of hydrophobic/hydrophilic moieties in different fractions of HA0. Subsequently, the amphiphilic nature of HA2 will have a substantial effect on interfacial interactions and subsequent self-assembly of HA0’s components.