Ion-Specific and pH-Dependent Hydration of Mica–Electrolyte Interfaces

Abstract

Hydration forces play a crucial role in a wide range of phenomena in physics, chemistry, and biology. Here, we study the hydration of mica surfaces in contact with various alkali chloride solutions over a wide range of concentrations and pH values. Using atomic force microscopy and molecular dynamics simulations, we demonstrate that hydration forces consist of a superposition of a monotonically decaying and an oscillatory part, each with a unique dependence on the specific type of cation. The monotonic hydration force gradually decreases in strength with decreasing bulk hydration energy, leading to a transition from an overall repulsive (Li+, Na+) to an attractive (Rb+, Cs+) force. The oscillatory part, in contrast, displays a binary character, being hardly affected by the presence of strongly hydrated cations (Li+, Na+), but it becomes completely suppressed in the presence of weakly hydrated cations (Rb+, Cs+), in agreement with a less pronounced water structure in simulations. For both aspects, K+ plays an intermediate role, and decreasing pH follows the trend of increasing Rb+ and Cs+ concentrations.

Forces between solid surfaces in aqueous electrolyte solutions

“…A planar metal substrate under potentiostatic control has also been studied with the colloidal probe [55][56][57]. One can also perform force measurements with the AFM by means of a sharp tip [58][59][60]. This approach allows to measure forces at smaller separations, but at the expense of lessdefined measurement geometry.…”

Quantitative Investigation on the Contributing Factors to the Contact Angle of the CO2/H2O/Muscovite Systems Using the Frumkin-Derjaguin Equation

“…In 2019, Van Lin et al measured the hydration forces acting on mica surfaces and determined parameters in empirical formulations at different ions, salinity, and pH. The empirical model consists of two terms: monotonically exponential decaying curve and the decaying oscillation curve [32]. The disjoining pressure is determined by their magnitudes and the decay lengths [33], so Π hyd is obtained as follows:…”

“…Variations of the magnitudes at pH 3.5 and 4.5 are probably within the range of values at pH from 2.5 to 8.5. Sensitivity analysis was carried out in these ranges using parameters by Van Lin et al [32]. Both magnitudes can change from half to twice of those at pH 3.5 or 4.5, so the horizontal axis is from -50% to 200%.…”

“…Hydration forces Π hyd ðhÞ at different pHs (2.5, 3.5, 4.5, and 8.5) based on the hydration force curves[32].…”

Long-range hydrodynamic forces in liquid FM-AFM

“…Performing AFM in liquids is of a great interest, in particu lar with biological samples which need to remain immersed [4] or to study molecules or ion adsorption at solid interfaces [5,6]. Contact mode and dynamic AFM mode have been intens ively used leading to high-resolution imaging of biological samples and high speed monitoring of biological processes [7].…”