Topology-Independent Water Extrusion from Hydrophobic Nanopores above 200 °C.

The wetting-dewetting of liquids in nanoporous solids is central to nanofluidics, separation, and energy storage, yet its temperature dependence under extreme conditions remains poorly understood. Here, we investigate water intrusion-extrusion in ordered mesoporous silica (SBA-15) functionalized with octyl groups (SBA-15-C8) across 25-250 °C and compare it with hydrophobized silica of disordered porosity. Intrusion pressures in both systems follow the expected negative temperature dependence described by classical capillarity. In contrast, extrusion pressures reveal a striking topology-temperature interplay. Up to 175 °C, SBA-15-C8 releases water at near-ambient pressure, unlike its disordered counterpart. Above 200 °C, however, extrusion from ordered pores converges to the high-pressure behavior of disordered silica, indicating a loss of topological distinction. Atomistic simulations suggest that this transition originates from thermally induced restructuring of the grafted layer: chain stretching effectively narrows the pores and may induce a Cassie-Baxter-like state, enhancing hydrophobicity and facilitating vapor nucleation. These findings demonstrate that pore topology ceases to govern extrusion at elevated temperatures, instead being dictated by a temperature-driven surface reconfiguration. The results contribute to a fundamental understanding of capillarity under extreme confinement and open opportunities for exploiting high-temperature wetting/dewetting in energy conversion, damping, and thermal management technologies.