Gas molecules sandwiched in hydration layers at graphite/water interfaces

Area of Science:

• Solid-liquid interfaces
• Surface science
• Physical chemistry

Background:

• Hydration structures are crucial at solid/liquid interfaces, influencing many phenomena.
• Dissolved gases form adsorbed layers on hydrophobic surfaces, but their relationship with hydration structures is unclear.

Purpose of the Study:

• Investigate the relationship between hydration structures and adsorbed gas layers at a highly ordered pyrolytic graphite/pure water interface.

Main Methods:

• Employed frequency-modulation atomic force microscopy (FM-AFM) to probe the interface.
• Applied strong load force with the AFM tip to penetrate adsorbed gas layers and record frequency shift curves.

Main Results:

• Adsorbed gas layers were found in low water density regions, sandwiched between high water density hydration layers.
• The distance between hydration layers was larger than simulation predictions and unaffected by the presence of gas layers.

Conclusions:

• Gas molecules interact with hydration structures before forming adsorbed layers, influencing and extending the distance between hydration layers.
• The findings reveal a novel interaction mechanism at hydrophobic solid-liquid interfaces.