Capillarity-driven transport in nanoporous solids is widespread in nature and crucial for modern liquid-infused engineering materials. During imbibition, curved menisci driven by high negative Laplace pressures exert an enormous contractile load on the porous matrix. Due to the challenge of simultaneously monitoring imbibition and deformation with high spatial resolution, the resulting coupling of solid elasticity to liquid capillarity has remained largely unexplored. Here, we study water imbibition in mesoporous silica using optical imaging, gravimetry, and high-resolution dilatometry. In contrast to an expected Laplace pressure-induced contraction, we find a square-root-of-time expansion and an additional abrupt length increase when the menisci reach the top surface. The final expansion is absent when we stop the imbibition front inside the porous medium in a dynamic imbibition-evaporation equilibrium, as is typical for transpiration-driven hydraulic transport in plants, especially in trees. These peculiar deformation behaviors are validated by single-nanopore molecular dynamics simulations and described by a continuum model that highlights the importance of expansive surface stresses at the pore walls (Bangham effect) and the buildup or release of contractile Laplace pressures as menisci collectively advance, arrest, or disappear. Our model suggests that these observations apply to any imbibition process in nanopores, regardless of the liquid/solid combination, and that the Laplace contribution upon imbibition is precisely half that of vapor sorption, due to the linear pressure drop associated with viscous flow. Thus, simple deformation measurements can be used to quantify surface stresses and Laplace pressures or transport in a wide variety of natural and artificial porous media.

中文翻译：

---

纳米孔吸水变形动力学


纳米多孔固体中毛细管驱动的传输在自然界中广泛存在，对于现代液体注入工程材料至关重要。在吸入过程中，由拉普拉斯高负压驱动的弯曲半月板对多孔基质施加巨大的收缩载荷。由于以高空间分辨率同时监测吸入和变形的挑战，由此产生的固体弹性与液体毛细管现象的耦合在很大程度上仍未得到探索。在这里，我们利用光学成像、重力测定法和高分辨率膨胀测定法研究介孔二氧化硅中的吸水性。与预期的拉普拉斯压力引起的收缩相反，当弯液面到达顶面时，我们发现时间平方根膨胀和额外的突然长度增加。当我们在动态吸入-蒸发平衡中停止多孔介质内的吸入前沿时，最终的膨胀不存在，这对于植物（尤其是树木）中蒸腾驱动的水力运输是典型的。这些奇特的变形行为通过单纳米孔分子动力学模拟进行了验证，并通过连续体模型进行了描述，该模型强调了孔壁处膨胀表面应力（Bangham 效应）以及随着弯月面集体前进、停止而形成或释放收缩拉普拉斯压力的重要性。 ，或消失。我们的模型表明，这些观察结果适用于纳米孔中的任何吸入过程，无论液体/固体组合如何，并且由于与粘性流相关的线性压降，吸入时的拉普拉斯贡献恰好是蒸气吸附的一半。 因此，简单的变形测量​​可用于量化表面应力和拉普拉斯压力或各种天然和人造多孔介质中的传输。