Anomalously Large Screening Lengths in Highly Concentrated Electrolytes: A Matter of Experimental Conditions

Abstract

Considerable debate exists about anomalous underscreening. Whilst surface force apparatus (SFA) measurements have confirmed anomalously large screening lengths ($\lambda$) in concentrated aqueous electrolytes, colloidal probe atomic force microscopy (CP-AFM) measurements have not. We demonstrate that by tuning experimental conditions, similarly large $\lambda$ can be achieved in concentrated aqueous LaCl${}_3$ electrolytes with CP-AFM. Structural forces were also observed at high LaCl${}_3$ concentrations, which we suggest stem from the formation of diffuse ion clusters, and that the remaining counter-ions yield the large deduced $\lambda$.