Pentyl grafting density thresholds for H2–water wettability on the (001) α-quartz surface under conditions relevant to underground hydrogen storage
Abstract
Underground hydrogen storage (UHS) in quartz-rich porous media is influenced by H2–water–mineral wettability. On quartz pore walls with mixed surface chemistry, H2–water–quartz wettability depends on the relative exposure of water-accessible silanol sites and nonpolar organic groups. This work identifies the pentyl grafting density range at which C5H11 coverage weakens silanol-controlled H2–water wetting and shifts the droplet boundary towards a pentyl-rich outer layer. Classical molecular dynamics simulations were performed at 300 K and 10 MPa on a fully hydroxylated (001) α-quartz reference surface and on pentyl-grafted surfaces ranging from 0.29 to 4.64 C5H11/nm2. The apparent contact angle (θApp) increased nonlinearly with pentyl grafting density. The fully hydroxylated surface and surfaces up to 0.87 C5H11/nm2 remained in the strongly water-wet regime. θApp entered the weakly water-wet regime at 1.16–1.45 C5H11/nm2 and the intermediate regime at 1.74–2.03 C5H11/nm2, before exceeding 90° at 2.32 C5H11/nm2. The laterally continuous contact line on the hydroxyl plane was lost beyond 1.45 C5H11/nm2. At dense grafting, θApp changed only slightly from 3.48 to 4.64 C5H11/nm2. Pressure variation across 5–50 MPa produced modest changes, most evident at intermediate grafting densities, but did not alter the wetting regimes established by surface chemistry. The transition was governed by reduced water access to surface OH groups as the pentyl-rich outer layer became the effective wetting surface. These findings provide a molecular-scale basis for assessing the effects of surface chemistry on quartz wettability in UHS studies.
Keywords
contact angle, molecular dynamics, pentyl grafting, quartz wettability, silanol masking, underground hydrogen storage
Document Type
Journal Article
Date of Publication
12-1-2026
Article Number
124071
E-ISSN
2352152X
Volume
180
Publication Title
Journal of Energy Storage
Publisher
Elsevier
School
School of Engineering
Funding received from the Australian Research Council (ARC)
DP220102907
Administering Institution
Edith Cowan University
Copyright
subscription content
Recommended Citation
Ismail, A. S., Keshavarz, A., & Iglauer, S. (2026). Pentyl grafting density thresholds for H2–water wettability on the (001) α-quartz surface under conditions relevant to underground hydrogen storage. Journal of Energy Storage, 180, 124071. https://doi.org/10.1016/j.est.2026.124071