Ion-specific long-range correlations on interfacial water driven by hydrogen bond fluctuations

Area of Science:

• Physical Chemistry
• Surface Science
• Solution Chemistry

Background:

• Interfacial water plays a crucial role in natural processes.
• Specific ion effects at interfaces are hypothesized to stem from unique water properties.
• Understanding these effects is key to various chemical and biological phenomena.

Purpose of the Study:

• To elucidate the mechanism behind specific ion effects in interfacial water.
• To investigate the relationship between ion correlations and water network structure.
• To determine how ion behavior changes at water percolation thresholds.

Main Methods:

• Utilized in situ online electrospray mass spectrometry.
• Measured halide ion ratios ([I-]/[Br-]) in water-alcohol microfilms.
• Systematically varied alcohol molar fractions (methanol and isopropanol) and added perchlorate ions.

Main Results:

• Observed that perchlorate ions influence halide ratios at low concentrations (0.1 μM).
• Detected peak effects at specific molar fractions corresponding to water percolation thresholds (x(ME) ~ 0.40, x(IP) ~ 0.15).
• Found that stronger correlations occur between ions with similar surface propensities, suggesting interfacial propagation.

Conclusions:

• Ion-specific long-range correlations are directly tied to amplified fluctuations at water percolation thresholds.
• The mechanism involves maximized water cluster sizes and interionic connections at these thresholds.
• Ion correlations preferentially propagate along two-dimensional interfacial layers.