Effects of the curvature of carbon nanotubes on the structure and thermodynamics of adsorbed water

Adsorbed water on carbon nanotubes (CNTs) exhibits unique structural and thermodynamic properties because of surface curvature; however, the curvature dependence of these properties has not been fully clarified. In this study, we conducted classical molecular dynamics simulation to investigate the curvature effects on different adsorption states with as many as two water-layers. When the adsorption water layer is a single layer, the adsorbed water forms a rhombic crystalline ice structure, organizing into an ice nano-ring. Its melting point and dewetting temperature are dependent on the curvature of the CNT and the hydrogen bond distances. By contrast, when the adsorbed water forms two layers, the structure is an amorphous configuration primarily composed of pentamers and hexamers; this structure undergoes a glass transition and exhibits dynamic heterogeneity at temperatures near the glass transition temperature, irrespective of the curvature. This behavior corresponds to the solid-liquid crossover observed in photoluminescence experiments.