Molecular-scale origin of extreme disjoining pressure in water confined in carbon and silica nanopores

Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2026. Vol. 736. Article 139693.

Ekaterina G. Odintsova, Darya L. Gurina, Yury A. Budkov

The behavior of water under nanoscale confinement is crucial for numerous technologies; yet predicting its
properties remains challenging due to the complex interplay of pore geometry and surface chemistry. While the
influence of general hydrophilicity is recognized, the specific role of the flexibility of surface functional groups - a
key molecular-scale feature - has remained underexplored. To address this, we conducted systematic molecular
dynamics simulations to investigate the structure and disjoining pressure of water confined in slit nanopores
(0.6–10 nm) with distinctly different surface chemistries: hydrophobic carbon, non-hydroxylated silica, and
hydroxylated silica with both mobile and immobilized hydroxyl groups. Our results reveal that strong
confinement (h < 2 nm) induces pronounced water layering, generating extreme tangential pressures. A central
finding is the critical role of hydroxyl group mobility: hydrophilic silica pores induce profoundly negative disjoining
pressure (-90 kbar at 0.6 nm), signifying strong effective attraction between walls, while hydroxylation
significantly mitigates local stresses. Mobile hydroxyl groups promote a more stable hydration structure than
rigid ones, acting as a molecular buffer. In contrast, hydrophobic carbon pores exhibit weaker attraction and a
more liquid-like water state. The novelty of our work lies in isolating and quantifying the effect of surface group

Keywords: Capillarity, Disjoining pressure, Расклинивающее давление, классическая молекулярная динамика, Капиллярные эффекты, classical molecular dynamics