Topology-Controlled Dipolar Ordering and Wetting Thermodynamics of Water in Hydrophobic Nanotubes

Classical capillarity does not fully describe water confined in hydrophobic nanopores, where nanoscale confinement fundamentally modifies the thermodynamics of the confined liquid. Using a family of model hydrophobic nanopores that enables independent control of wall thickness, confinement topology, and water-surface interaction strength, we demonstrate that water intrusion is governed not only by surface hydrophobicity but also by pore topology. Comparison of nanotubes with two open ends, shell-coated nanotubes, and nanotubes closed at one end separates the effects of the external shell and broken axial symmetry. The shell modifies the interaction environment surrounding the confined water, reducing the effective hydrophobicity of the nanopore, whereas closing one end stabilizes a single polarized water domain. Orientational ordering develops already in the liquid state, prior to crystallization, and contributes an additional electrostatic component to the free energy landscape. Consistent with the systematic reduction of intrusion pressure, the reconstructed free energy profiles indicate a progressive decrease in the estimated activation barrier from open to closed nanotubes. These results identify confinement topology as an independent parameter governing the thermodynamics of confined water and establish a direct connection between collective dipolar organization and intrusion behavior, providing new design principles for nanoporous and nanofluidic materials with tunable wetting properties.