Colloidal Probe Atomic Force Microscopy Reveals Anomalous Underscreening: A Matter of Experimental Conditions

TL;DR

This study demonstrates that by adjusting experimental conditions, colloidal probe atomic force microscopy can observe anomalous underscreening in concentrated electrolytes, aligning with surface force apparatus results and suggesting electrolyte ordering effects.

Contribution

It is the first to observe anomalous underscreening with CP-AFM by replicating SFA conditions, bridging a gap between different measurement techniques.

Findings

CP-AFM can detect anomalous underscreening under specific conditions.

Experimental conditions significantly influence screening length measurements.

Results suggest electrolyte ordering impacts screening behavior.

Abstract

There is considerable debate about anomalous underscreening in highly concentrated electrolytes: While surface force apparatus (SFA) measurements have confirmed anomalously long screening lengths, so far they have not yet been detected in experiments using colloidal probe atomic force microscopy (CP-AFM). CP-AFM measurements across aqueous LaCl$_3$ solutions demonstrate that by adapting the experimental conditions to those of SFA studies, similarly large screening lengths can be achieved at high salt concentrations. This represents the first observation of anomalous underscreening with CP-AFM. These findings leave room for speculations about the ordering of the confined electrolyte.