Competing hydrogen-bond orders drive water's anomalous surface tension.

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Physics

Background:

• Water's surface tension exhibits a complex, nonlinear temperature dependence.
• A key feature is the reentrant increase in surface tension within the supercooled regime, a phenomenon not fully explained by existing models.

Purpose of the Study:

• To elucidate the microscopic structural mechanisms underlying water's nonlinear surface tension.
• To establish a link between molecular ordering and macroscopic interfacial properties.

Main Methods:

• Molecular dynamics simulations were employed to investigate water's behavior at the molecular level.
• Analysis focused on the interplay between different molecular states (ρ-states and S-states) and their structural anisotropies.

Main Results:

• Surface tension is governed by the anisotropic interplay of ρ-states (O-H alignment) and S-states (tetrahedral ordering).
• The reentrant rise in surface tension upon supercooling is attributed to the increased orientational order of S-states.

Conclusions:

• A unified structural framework explains the temperature dependence of water's surface tension, including inflection points.
• This work establishes a direct link between hydrogen-bond motifs, interfacial stress, and macroscopic behavior, with broad implications.