The locality of surface interactions on colloidal probes

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.