Nanoplatelet interactions in the presence of multivalent ions: The effect of overcharging and stability

Maria Jansson; Domagoj Belić; Jan Forsman; Marie Skepö

doi:10.1016/j.jcis.2020.06.045

Nanoplatelet interactions in the presence of multivalent ions: The effect of overcharging and stability

J Colloid Interface Sci. 2020 Nov 1:579:573-581. doi: 10.1016/j.jcis.2020.06.045. Epub 2020 Jun 19.

Authors

Maria Jansson¹, Domagoj Belić², Jan Forsman³, Marie Skepö⁴

Affiliations

¹ Theoretical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden. Electronic address: maria.jansson@teokem.lu.se.
² Physical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
³ Theoretical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
⁴ Theoretical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden; LINXS - Lund Institute of Advanced Neutron and X-ray Science, Scheelevägen 19, SE-223 70 Lund, Sweden. Electronic address: marie.skepo@teokem.lu.se.

PMID: 32623123
DOI: 10.1016/j.jcis.2020.06.045

Abstract

Hypothesis: The stability of colloidal dispersions in the presence of multivalent ions depends strongly on the electrostatic interactions between the suspended particles. Of particular interest are colloidal particles having dimensions in the nanometric range and with an anisotropic shape due to its high surface area per unit mass, for example clay, which has the key characteristic of a negatively charged surface, surrounded by an oppositely charged rim.

Experiments: In this study, we investigate the interactions in nanoplatelet dispersions for the model system of Laponite® clay with addition of mono- and multivalent salt. Molecular dynamics simulations with enhanced umbrella sampling have been utilised in combination with the experimental techniques of zeta-potential measurements, dynamic light scattering, and transmission electron microscopy.

Findings: It was observed that tactoid formation and tactoidal dissolution due to overcharging occur upon the addition of trivalent salt. The overcharging effect was captured from calculated potential of mean force and confirmed from the zeta-potential, which changed sign from negative to positive when increasing the stoichiometric charge-ratio between the positive salt ions and the clay. Consequently, the gained information could provide useful physical insight of nanoplatelet interactions in the presence of multivalent ions.

Keywords: Clay; Cryo-TEM; Laponite®; Molecular dynamics simulations; Multivalent ions; Nanoplatelet; Overcharging; Potential of mean force; Stability; Zeta-potential.