Hydration layer structure modulates superlubrication by trivalent La³⁺ electrolytes.

Area of Science:

• Tribology
• Surface Chemistry
• Materials Science

Background:

• Aqueous lubricants are vital for various applications, with hydrated ion layers on surfaces dictating their lubricating properties.
• The prevailing view is that hydration lubrication structures are invariant.

Purpose of the Study:

• To investigate how ion surface coverage influences hydration layer structure and lubricating properties.
• To explore lubrication mechanisms under subnanometer confinement.

Main Methods:

• Characterization of hydration layer structures using aqueous trivalent electrolytes.
• Analysis of friction coefficients and energy dissipation pathways.

Main Results:

• Demonstrated that ion surface coverage dictates hydration layer roughness and lubricating behavior.
• Identified two superlubrication regimes (friction coefficients 10^-4 and 10^-3) dependent on hydration layer structure and thickness.
• Observed distinct energy dissipation pathways and structure-dependent behaviors for each regime.

Conclusions:

• Established a direct link between dynamic boundary lubricant film structure and tribological performance.
• Proposed a molecular-level framework for studying the relationship between hydration layer structure and lubrication.
• Challenged the invariance assumption in hydration lubrication, highlighting the role of ion coverage.