Colloidal particle-surface interactions in atmospheric and aquatic systems
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Colloidal particles suspended in a liquid or gas phase often interact with a solid-liquid or solid-gas interface. In this study, experimental data through atomic force microscopy and neutron reflectometry and theoretical results of colloidal particle-surface interactions were obtained and compared. Atmospheric and aquatic environments were considered for the interactions of microbial colloidal particles and nano-sized silica particles with planar surfaces. Spores of Bacillus thuringiensis, members of the Bacillus cereus group, were examined as the microbial particles, simulating the pathogens Bacillus cereus and Bacillus anthracis which are potentially dangerous to human health. Model planar surfaces used in this study include gold which is an electrically conductive surface, mica which is a highly charged, nonconductive surface, and silica. In atmospheric systems, the interaction forces were found to be strongly affected by the relative humidity, and the total adhesion force of a particle onto a surface was modeled as the addition of the capillary, van der Waals, and electrostatic forces. Each component is influenced by the properties of the particle and surface materials, including hydrophobicity and surface roughness, as well as the humidity of the surrounding atmosphere. In aquatic systems, the interaction forces are mainly affected by the solution chemistry, including pH and ionic strength. The main components of the interaction force between a microbial colloidal particle and a planar surface were found to be the van der Waals and electrostatic forces. The results obtained in this research provide insights into the fundamental mechanisms of colloidal particle interactions with environmental surfaces in both atmospheric and aquatic systems, contributing to the understanding of the phenomena driving such interfacial processes as deposition, aggregation, and sedimentation. Thus, the results can help us describe the behavior of contaminant colloidal particles in environmental systems and subsequently devise better means for their removal from environmental surfaces.