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(225b) Mechanism of Enhanced Aggregation of Alginate-Coated Hematite Nanoparticles in the Presence of Calcium, Strontium, and Barium Cations

Chen, K. L., The Johns Hopkins University
Mylon, S. E., Lafayette College
Elimelech, M., Yale University

The aggregation kinetics of alginate-coated hematite nanoparticles are investigated in the presence of various divalent electrolytes through time-resolved dynamic light scattering. The coated nanoparticles undergo aggregation mechanism controlled by electrostatic interactions in the presence of magnesium and monovalent cations such as sodium. However, the presence of calcium, strontium, and barium cations lead to enhanced aggregate growth through alginate-gel network formation and subsequent bridging of the nanoparticles. The enhanced aggregation mechanism is further investigated by measuring the force between a hematite colloidal probe and a layer of hematite nanoparticles deposited on a quartz surface in the presence of alginate via AFM. The approach and retraction force analysis provides information on the interactions between the aggregating alginate-coated nanoparticles and the structure of the aggregates formed. Preliminary results show that in the presence of sodium and magnesium cations, the adhesion forces are weak and short-ranged. However, long-range interaction forces as well as multiple discontinuities in the retraction force profiles are noted when the colloidal probe is retracted from the substrate surface in the presence of calcium, strontium, and barium cations, indicating the ?pulling-off? of several alginate polymer linkages between the probe and substrate.