Double-layer force suppression between charged microspheres

TL;DR

This paper introduces a protocol to completely suppress double-layer electrostatic forces between charged microspheres by tuning the metallic sphere's potential, enabling clearer measurements of other surface forces like Casimir interactions.

Contribution

The study presents a novel method to control double-layer forces using potential tuning, revealing significant differences from traditional approximation predictions.

Findings

Double-layer force can be fully suppressed by tuning the metallic sphere's potential.

Suppression values differ notably from proximity force approximation predictions.

Method enables clearer measurement of non-electrostatic surface interactions.

Abstract

In this paper we propose a protocol to suppress double-layer forces between two microspheres immersed in a dielectric medium, being one microsphere metallic at a controlled potential {\psi}M and the other a charged one either metallic or dielectric. The approach is valid for a wide range of distances between them. We show that, for a given distance between the two microspheres, the double-layer force can be totally suppressed by simply tuning {\psi}M up to values dictated by the linearized Poisson-Boltzmann equation. Our key finding is that such values can be substantially different from the ones predicted by the commonly used proximity force approximation (PFA), also known as Derjaguin approximation, even in situations where the latter is expected to be accurate. The proposed procedure can be used to suppress the double-layer interaction in force spectroscopy experiments, thus paving the way for measurements of other surface interactions, such as Casimir dispersion forces.