The locality of surface interactions on colloidal probes

TL;DR

This paper investigates how local surface geometry variations on colloidal probes affect short-range surface interactions, revealing that common roughness assumptions may lead to significant uncertainties in experimental-theoretical comparisons.

Contribution

It provides an extensive experimental and numerical analysis of colloidal surface topologies, highlighting the impact of local curvature variations on interaction measurements.

Findings

Local surface curvature varies significantly on colloidal probes.

Surface topology influences the accuracy of interaction force comparisons.

Common roughness assumptions may not be valid for micro-sphere experiments.

Abstract

The Casimir and electromagnetic interactions between objects at short separations are strongly influenced by the local geometry near the point of closest approach. In this paper we demonstrate that the assumptions underlying common statistical analysis of roughness may not hold in experiments using micro-spheres as interacting objects. Based on an extensive experimental and numerical analysis of the surface topology of the widely used colloidal particle types 4310A and 4320A, we show that the actual variation in the local surface curvature may give rise to large uncertainties in the comparison of experimental data to theories.