It is commonly true that a diluted colloidal suspension is more stable over time than a concentrated one, because dilution reduces collision rates, so delays formation of aggregates. However, the research team observed the opposite relationship between stability and concentration for some engineered ligand-coated nanoparticles
Because the stability of nanoparticles determines their physicochemical and kinetic behavior including toxicity, dilution induced instability needs to be understood to realistically predict the behavior of engineered ligand-coated nanoparticles in aqueous systems.
It is commonly true that a diluted colloidal suspension is more stable over time than a concentrated one, because dilution reduces collision rates of the particles and therefore delays formation of aggregates. However, this generalization does not apply for some engineered ligand-coated nanoparticles (NPs). The researchers observed the opposite relationship between stability and concentration of NPs. They tested four different types of NPs; CdSe-11-mercaptoundecanoic acid, CdTe-polyelectrolytes, Ag-citrate, and Ag-polyvinylpirrolidone. The results showed that dilution alone induced aggregation and subsequent sedimentation of the NPs that were originally monodispersed at very high concentrations. Increased dilution caused NPs to progressively become unstable in the suspensions. The extent of the dilution impact on the stability of NPs is different for different types of NPs. The team hypothesizes that the unavoidable decrease in free ligand concentration in the aqueous phase following dilution causes detachment of ligands from the suspended NP cores. The ligands attached to NP core surfaces must generally approach exchange equilibrium with free ligands in the aqueous phase; therefore, ligand detachment and destabilization are expected consequences of dilution. More studies are necessary to test this hypothesis. Because the stability of NPs determines their physicochemical and kinetic behavior including toxicity, dilution-induced instability needs to be understood to realistically predict the behavior of engineered ligand-coated nanoparticles in aqueous systems.
BER Program Manager
David Lesmes, SC-23.1
Jiamin Wan, LBNL
Support for the project is through the Subsurface Biogeochemical Research program of the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, under contract DE-AC02- 05CH11231.
Wan, J., Y. Kim, M.J. Mulvihill, and T. K. Tokunaga. "Dilution destabilizes engineered ligand-coated nanoparticles in aqueous suspensions." Environmental Toxicology and Chemistry 37(5), 1301–1308 (2018). [DOI:10.1002/etc.4103].
SC-33.1 Earth and Environmental Sciences Division, BER
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