Characterizing\nthe Orderliness of Interfacial Water\nthrough Stretching Vibrations

Spatial orderliness, which is the orderly structure of\nmolecules,\ndiffers significantly between interfacial water and bulk water. Understanding\nthis property is essential for various applications in both natural\nand engineered environments. However, the subnanometer thickness of\ninterfacial water presents challenges for direct and rapid characterization\nof its structural orderliness. Herein, through molecular dynamics\nsimulations and infrared spectral analysis of interfacial water in\na graphene slit pore, we reveal a hyperbolic tangent relationship\nbetween the water ordering and its O–H stretching information\nin the infrared spectrum. Specifically, O–H symmetric stretching\ndominated in the highly ordered water structure, while a transition\nto the asymmetric stretching corresponded to an increase in the degree\nof disorder. Thus, the O–H stretching behavior could serve\nas a useful and quick assessment of the orderliness of interfacial\nwater. This work provided insights into interfacial water’s\nunique molecular network and structural dynamics and identified the\nstretching vibrations’ key role in its degree of order, providing\ninsight for fields such as nanotechnology, biology, and material science.