An in-depth knowledge of the interaction of water with amorphous silica is critical to fundamental studies of interfacial hydration water, as well as to industrial processes such as catalysis, nanofabrication, and chromatography. Silica has a tunable surface comprising hydrophilic silanol groups and moderately hydrophobic siloxane groups that can be interchanged through thermal and chemical treatments. Despite extensive studies of silica surfaces, the influence of surface hydrophilicity and chemical topology on the molecular properties of interfacial water is not well understood. In this work, we controllably altered the surface silanol density, and measured surface water diffusivity using Overhauser dynamic nuclear polarization (ODNP) and complementary silica–silica interaction forces across water using a surface forces apparatus (SFA). The results show that increased silanol density generally leads to slower water diffusivity and stronger silica–silica repulsion at short aqueous separations (less than ∼4 nm). Both techniques show sharp changes in hydration properties at intermediate silanol densities (2.0–2.9 nm⁻²). Molecular dynamics simulations of model silica–water interfaces corroborate the increase in water diffusivity with silanol density, and furthermore show that even on a smooth and crystalline surface at a fixed silanol density, adjusting the spatial distribution of silanols results in a range of surface water diffusivities spanning ∼10%. We speculate that a critical silanol cluster size or connectivity parameter could explain the sharp transition in our results, and can modulate wettability, colloidal interactions, and surface reactions, and thus is a phenomenon worth further investigation on silica and chemically heterogeneous surfaces.

对水与无定形二氧化硅相互作用的深入了解对于界面水合水的基础研究以及催化，纳米加工和色谱等工业过程至关重要。二氧化硅具有包含亲水性硅烷醇基团和中等疏水性硅氧烷基团的可调表面，可以通过热处理和化学处理进行互换。尽管对二氧化硅表面进行了广泛的研究，但对表面亲水性和化学拓扑结构对界面水分子性质的影响尚不十分了解。在这项工作中，我们可控地改变了表面硅烷醇的密度，并使用表面力仪器（SFA）使用Overhauser动态核极化（ODNP）和互补的二氧化硅-二氧化硅相互作用力来测量表面水的扩散率。结果表明，在较短的水相分离（小于约4 nm）下，提高的硅烷醇密度通常会导致较慢的水扩散性和更强的硅胶-二氧化硅排斥力。两种技术都表明，在中等硅醇密度（2.0–2.9 nm）下，水合特性发生了急剧变化。^-2）。二氧化硅-水界面模型的分子动力学模拟证实了水扩散率随硅烷醇密度的增加而增加，并且进一步表明，即使在光滑且结晶的表面上，以固定的硅烷醇密度，调整硅烷醇的空间分布也会导致一定范围的表面水扩散率跨度约为10％。我们推测，关键的硅烷醇簇尺寸或连通性参数可以解释我们结果的急剧转变，并且可以调节润湿性，胶体相互作用和表面反应，因此，这是值得在二氧化硅和化学非均质表面上进行进一步研究的现象。