Molecular Dynamics Study of the Adsorption of Phenolic Molecules at the Silica–Water Interface

Abstract

Many aquatic organisms adhere strongly to mineral surfaces, motivating a molecular-level understanding of the interactions governing adhesion at aqueous interfaces. Here, classical molecular dynamics simulations were used to investigate phenol, catechol, and gallol at a hydroxylated silica–water interface across four solute loadings. Density profiles revealed near-surface enrichment of all three phenolics and a characteristic double peak in the phenolic hydroxyl-oxygen density, consistent with silica-induced interfacial layering. The inner peak represents hydroxyl groups directly hydrogen-bonded to surface silanols, whereas the outer peak corresponds to a second surface-directed sublayer within the adsorption region. Orientational analysis showed that phenol and catechol preferentially adopt relatively flat configurations near the surface, whereas gallol favors a more upright orientation, likely because its additional hydroxyl group enables stronger and more persistent interactions with silica. The total number of phenolic-silica hydrogen bonds increased with hydroxyl-group multiplicity in the order phenol < catechol < gallol. From the lowest loading (0.55 M) to the highest (4.40 M), the mean numbers of hydrogen bonds per frame increased from 0.06 to 0.47 for phenol, from 0.56 to 0.59 for catechol, and from 1.77 to 6.66 for gallol. These differences arose primarily from a greater number of polyhydroxylated molecules forming at least one surface hydrogen bond, while simultaneous multidentate binding remained comparatively uncommon. Continuous hydrogen-bond autocorrelation functions, which characterize uninterrupted individual bond lifetimes, were similar among the three solutes. By contrast, intermittent autocorrelation functions, which account for bond breaking and reformation, decayed most slowly for gallol and most rapidly for phenol. Thus, increasing hydroxyl-group multiplicity enhances persistent interfacial association through repeated hydrogen bonding without substantially extending the lifetime of individual bonds. Overall, these results demonstrate how hydroxyl-group multiplicity and solute loading jointly regulate interfacial enrichment, molecular orientation, and hydrogen-bond dynamics, providing molecular-level guidance for designing phenolic adhesives and coatings for silica–water interfaces.