Description
Recent surface forces apparatus experiments that measured the forcesbetween two mica surfaces and a series of subsequent theoretical studies
suggest the occurrence of universal underscreening in highly concentrated
electrolyte solutions. We performed a set of systematic Atomic
Force Spectroscopy measurements for aqueous salt solutions in a concentration
range from 1 mM to 5 M using chloride salts of various
alkali metals. Experiments were carried out using flat substrates and
submicrometer-sized colloidal probes made of smooth oxidized silicon
immersed in salt solutions at pH values of 6 and 9 and temperatures
of 25degC and 45 degC. While strong repulsive forces were observed
for the smallest tip-sample separations, none of the conditions explored
displayed any indication of anomalous long range electrostatic forces as
reported for mica surfaces. Instead, forces are universally dominated
by attractive van der Waals interactions at tip-sample separations beyond
approximately 2nm for salt concentrations of 1 M and higher.
Complementary calculations based on classical density functional theory
for the primitive model support these experimental observations
and display a consistent decrease in screening length with increasing
ion concentration.
| Period | 27 Mar 2023 |
|---|---|
| Event title | DPG Fruhjahrstagung SKM, Dresden 2023 |
| Event type | Conference |
| Location | Dresden, GermanyShow on map |