Hydration forces between mica surfaces in electrolyte solutions

The observation of hydration force with two decay lengths in 1 M NaAc indicates that cations gradually lost their hydration shells at small distances under high compression; the large decay length farther away corresponds to a layer of fully hydrated Na+ ions outside the innermost structure.

“The observation of the hydration force with two decay lengths indicated again that the cations gradually lost their hydration shells at small distances under high compression [57,58]; the large decay length farther away from the interface corresponds to a layer of fully hydrated Na + ions outside the innermost structure.”

The large energies associated with hydration of charges lead to hydration repulsion effects.

“The large energies associated with hydration of charges lead to hydration repulsion effects [55 -60]”

The same hydration effect can lead to strong short-ranged repulsion when two charged surfaces interact across a high-salt-concentration solution.

“The same hydration effect can also lead to strong short-ranged repulsion when two charged surfaces interact across a high-salt-concentration solution [55, 59].”

When charged surfaces interact across pure or low salt-concentration water, the counterions in the gap are mostly small hydrated protons which may readily condense into and neutralise negatively charged lattice sites, so surfaces come into adhesive van der Waals contact.

“When such surfaces interact across pure or low salt-concentration water, as shown in Fig. 1, the counterions in the gap are mostly small hydrated protons which, as the surfaces approach, may readily condense into, and neutralise, the negatively charged lattice sites, so they come into adhesive van der Waals contact.”

Interactions across high salt solutions above some critical hydration concentration (for Na+, K+ around 0.1-1.0 mM) may be very different.

“In contrast, interactions across high salt solutions, above some critical hydration concentration (which differs with the ion but for Na + , K + is around 0.1 -1.0 mM [57, 59]) may be very different”