Sulfidation modifies the macromolecular capping and thus the stability of engineered silver nanoparticles (AgNPs). The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, which includes a steric term to account for the stability brought about by the macromolecular capping, has been widely used to quantify the energy of interaction of AgNPs before and after sulfidation. However, existing calculations that superpose the steric term onto the classical DLVO model fail to include the changes of electrical double layer (EDL) repulsion and van der Waals (vdW) attraction after the overlap of soft capping layers from the two interacting surfaces. Using an interdigitation-compression model to describe the contact of the capping layers, an updated calculation for the DLVO energy of interaction between two macromolecule-coated flat plates was first derived by the Ohshima’s soft particle model for EDL repulsion and from a multilayer pair-wise summation for vdW attraction. This plate-plate interaction was then converted to the sphere-sphere (aggregation) or sphere-plate (deposition) geometry via surface element integration. Our calculation reveals that polyelectrolyte capping enhances EDL repulsion especially after the contact of the soft layers; vdW attraction is reduced because the silver core, which has a high Hamaker constant, is masked by the macromolecular capping. Because the macromolecular capping is stripped after sulfidation, the classical DLVO energy of interaction becomes more attractive (or less repulsive). To our knowledge, this calculation is the first that accounts mathematically for the effect of the capping layer for both the EDL repulsion and vdW attraction after the contact of soft layers; it helps explain particle stability in addition to the less quantitatively rigorous concept of steric hindrance. The enhanced or reduced stability by the change of the macromolecular capping highlights the importance of environmental transformation (e.g., sulfidation) in assessing the fate and transport of engineered AgNPs.

DLVO energy of interaction of macromolecule-coated silver nanoparticles

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.