Energetic and Structural Insights into Water Confined in Hydrophobic Nanopores

Water
confined within hydrophobic nanopores exhibits unusual thermodynamic
and structural behavior that governs a wide range of nanofluidic and
energy-conversion phenomena. Here, we combine high-pressure scanning
calorimetry with molecular dynamics simulations in the temperature
range of 298–380 K to elucidate the energetics and mechanisms
of water intrusion into pure-silica LTA zeolites featuring cage-like
pores. A new data-processing approach separates compression and intrusion
contributions in pressure–volume curves, enabling direct quantification
of temperature-dependent heat effects. Intrusion is exothermic at
ambient temperature (≈−5 J g–1) and
becomes nearly thermoneutral above 338 K. Simulations reveal slow
intrusion kinetics, collective cage filling through hydrogen-bond-mediated
chains, and pronounced stabilization at occupancies of 17–22
H2O molecules per supercell, balancing enthalpic and entropic
factors. The results demonstrate that intrusion pressures correlate
with accessible surface area, free pore volume, pore geometry, and
connectivity rather than aperture size, thereby invalidating classical
Laplace–Washburn scaling for nanopores. These findings establish
microscopic design principles for tailoring wetting thermodynamics
in hydrophobic nanoporous frameworks for energy storage, mechanical
actuation, nanofluidic systems, and nanodevices.

受限在疏水纳米孔中的水表现出反常的热力学与结构行为，该行为支配着诸多纳米流体与能量转换现象。本研究将高压扫描量热法与298–380开尔文温度区间内的分子动力学模拟相结合，以阐明水侵入具有笼状孔道的纯硅LTA沸石（LTA zeolite）的能量学与作用机制。我们提出一种全新的数据处理方法，可分离压力-体积曲线中的压缩与侵入贡献，从而实现对温度依赖的热效应的直接定量分析。室温下，水的侵入过程为放热反应（约−5 J·g⁻¹），当温度高于338 K时则趋近于热中性。分子动力学模拟结果显示，水的侵入动力学过程较为缓慢，通过氢键介导的链实现集体式笼填充，且当每个超胞的H₂O分子占据数为17~22时，体系呈现出显著的稳定化效应，该效应平衡了焓与熵的贡献。研究结果表明，侵入压力与可及表面积、自由孔体积、孔几何结构及孔道连通性相关，而非孔径尺寸，从而推翻了经典拉普拉斯-沃什本（Laplace–Washburn）标度律在纳米孔体系中的适用性。本研究的发现为调控疏水纳米多孔骨架的润湿热力学提供了微观设计原则，可应用于储能、机械驱动、纳米流体系统及纳米器件等领域。