Absence of anomalous underscreening in highly concentrated aqueous electrolytes confined between smooth silica surfaces

Ion adsorption and hydration forces: a comparison of crystalline mica vs. amorphous silica surfaces

“…This is contrast to many earlier reports using surface forces measurements with the SFA, colloidal probe AFM as well as regular (i.e. not too sharp) AFM tips 12,13,38,45,47,[55][56][57] . Our conclusion is thus that silica-water interfaces display an intrinsically oscillatory hydration structure similar to atomically smooth hydrophilic surfaces such as mica and calcite.…”

“…This tendency becomes even more pronounced for colloidal probe tips with a radii of 100nm and beyond, see e.g. [56][57][58] . To our knowledge, all previously reported systematic studies of hydration forces on silica surfaces were performed with tips with radii of 25nm and more.…”

Structure and anomalous underscreening in ethylammonium nitrate solutions confined between two mica surfaces

“…With the exponent  ≈ 3 across a range of experimental conditions. This phenomenon, in which charged bodies or surfaces interact in a manner that appears less screened than predicted by mean field theories, has been called 'underscreening' [14], or 'anomalous underscreening' [15].…”

Colloidal Interactions in Ionic Liquids– the electrical double layer inferred from ion layering and aggregation

“…Similarly, comprehensive AFM measurements between smooth silica surfaces using chloride salts of various alkali metals in the range from 1 mM to 5 M, showed no indication of anomalous long range electrostatic forces at temperatures of 25 °C and 45 °C, but instead attractive van der Waals interactions at tip-sample separations of ~2 nm and beyond for salt concentrations of 1 M and higher. 44 This calls for alternative analysis and understanding. Moreover, the proposed scaling law requires that the length scale of ions is well known.…”