Structural and Double Layer Forces between Silica Surfaces in Suspensions of Negatively Charged Nanoparticles.

Liam R J Scarratt,Katarzyna Kubiak,Plinio Maroni,Michal Borkovec,Gregor Trefalt

doi:10.1021/acs.langmuir.0c02917

Liam R J Scarratt, Katarzyna Kubiak + Show 3 more

Open Access

https://doi.org/10.1021/acs.langmuir.0c02917

Copy DOI

Abstract

Direct force measurements between negatively charged silica microparticles are carried out in suspensions of like-charged nanoparticles with atomic force microscopy (AFM). In agreement with previous studies, oscillatory force profiles are observed at larger separation distances. At smaller distances, however, soft and strongly repulsive forces are present. These forces are caused by double layer repulsion between the like-charged surfaces and can be quantitatively interpreted with the Poisson-Boltzmann (PB) model. However, the PB model must be adapted to a strongly asymmetric electrolyte to capture the nonexponential nature of these forces. Thereby, the nanoparticles are modeled as highly charged co-ions, while the counter ions are monovalent. This model permits extraction of the effective charge of the nanoparticles, which is well comparable to the one obtained from electrophoresis. The PB model also explains the presence of a particle-free layer close to the interface.

Highlights

The interactions feature oscillatory force profiles. These structural forces originate from the liquid-like structure of the nanoparticle suspensions
One observes soft and strongly repulsive forces, which lead to a particle-free layer close to the water-solid interface. These forces are caused by double layer repulsion between the likecharged surfaces
While these forces are strongly non-exponential, they can be quantitatively interpreted with the Poisson-Boltzmann (PB) model for asymmetric electrolytes. From this description, which is only valid at short distances, the effective charge of the nanoparticles can be extracted

Summary

Introduction

Concentrated suspensions of charged nanoparticles are relevant in numerous applications, such as, papermaking, ceramic processing, or food technology.[1,2,3,4,5] Such systems come again into focus of fundamental research due to recent reports of structural forces acting between like-charged surfaces.[6,7,8,9,10,11,12,13,14] These forces are normally probed in suspensions of negatively charged silica nanoparticles sandwiched between two silica surfaces by means the colloidal probe atomic force microscopy (AFM).[15,16,17] One typically observes oscillatory profiles with a wavelength of several nanometers featuring several of these oscillations. SCARRATT, Liam Ronald John, et al Structural and Double Layer Forces between Silica Surfaces in Suspensions of Negatively Charged Nanoparticles.

Results

Conclusion