Polymer surface coatings strongly affect colloid stability in a broad spectrum of important engineering processes. Polymers are used as flocculants or stabilizers in water and waste treatment, mineral processing, coal-water slurry stabilization, paint production, food colloid stabilization, separation of bacterial suspensions, paper making, brewing, ceramics fabrication, pharmaceutical preparation, and agrochemical formulation. The stability, mobility, and chemical reactively of colloidal particles naturally present in groundwater and other aquatic systems are strongly controlled by surface coatings of organic molecules. Since these particles influence the transport of chemical or radioactive contaminants and the survival of pathogenic microorganisms, the presence of organic-coated colloids must be accounted for in models that predict the fate of hazardous wastes in the environment. This research seeks to clarify the mechanisms by which surface-adsorbed polymers influences colloid stability in aqueous systems. Theoretical and experimental studies indicates that the stability of coated colloidal particles depends critically on the conformation of the adsorbing molecule. Despite the implied importance of polymer conformation on colloid stability, there are no experimental techniques which directly measure the conformation of adsorbed polymers. A major goal of this research is to develop a method for examining the conformation of single-stranded DNA molecules adsorbed to colloidal latex particles using a technology called "DNA footprinting". This technology, originally developed by biochemists to investigate protein/DNA interactions, will be used to ascertain the fraction of adsorbed DNA that is distributed between trains, loops and tails. The response of this distribution to changes in surface and solution chemistry will be investigated and related to concomitant changes in colloid stability.
