Can nanoscale surface charge heterogeneity really explain colloid detachment from primary minima upon reduction of solution ionic strength?

Authors: SHEN, CHONGYANG - China Agriculture University; Bradford, Scott; LI, TIANTIAN - China Agriculture University; LI, BAOGUO - China Agriculture University; HUANG, YUANFANG - China Agriculture University

Submitted to: Journal of Nanoparticle Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2018
Publication Date: 6/18/2018
Citation: Shen, C., Bradford, S.A., Li, T., Li, B., Huang, Y. 2018. Can nanoscale surface charge heterogeneity really explain colloid detachment from primary minima upon reduction of solution ionic strength? Journal of Nanoparticle Research. 20:165. https://doi.org/10.1007/s11051-018-4265-8.
DOI: https://doi.org/10.1007/s11051-018-4265-8

Interpretive Summary: Rainfall, irrigation, and runoff water can change the chemistry of soil water and groundwater, and thereby induce the release and transport of colloids such as microorganisms, clays, and nanoparticles to drinking water supplies. Theoretical calculations were conducted to better understand the cause of colloid release under these conditions. Results indicate that colloid release with a reduction in solution ionic strengthen was unlikely on smooth soil surfaces with positive charges, but easily occurred on rough soil surfaces. These results help to identify the relative importance of variability in roughness and charge on colloid release. This information will be of interest to scientists, engineers, regulators, and public health officials that are concerned with the release of colloids and associated contaminants into drinking water supplies.

Technical Abstract: This study theoretically examined colloid detachment from primary minima with ionic strength (IS) reduction on heterogeneous collector surfaces. The chemically and physically heterogeneous collector surfaces were modeled as a planar surface carrying nanoscale patches of different zeta potentials and nanoscale pillars/hemispheroids, respectively. The surface element integration technique was used to calculate interaction energies between colloid and collector surfaces. Two boundary conditions for the double-layer interaction energy were considered, namely constant surface potential (CSP), and linear superposition approximation (LSA). In contrast to prevailing opinions in the literature, our results show that colloids attached on the chemically heterogeneous surface cannot be detached by IS reduction under CSP condition due to an increase of the adhesive force/torque with decreasing IS. Detachment from chemically heterogeneous surfaces by IS reduction can occur under LSA condition only when the flow velocity is very high. In contrast, the presence of nanoscale physical heterogeneity can cause colloid detachment from primary minima by IS reduction under both CSP and LSA conditions at flow velocities commonly used in experimental studies because of a significant reduction in the adhesive forces/torques.