Nanoscale analysis of surface modifications on silanized glass: Wettability alteration and long-term stability

To investigate the effect of wettability on multiphase flow in porous media, hydrophilic glass surfaces are typically modified through a silanization process. Since wettability alteration arises from both chemical and structural changes, characterizing these modifications at the nanoscale is essential for understanding their impact on fluid displacement patterns. This study examines these nanoscale modifications across the relevant surface area of Surfasil-treated glass beads, using inverse gas chromatography and atomic force microscopy. The results show that silanization reduces both specific and dispersive components of surface energy, indicating fewer polar groups and lower total energy, leading to decreased hydrophilicity compared to untreated glass beads. Additionally, disproportionate reduction in surface energy components results in more pronounced adhesion loss for non-wetting fluids compared to wetting fluids. BET surface area measurements and AFM images reveal that the surface becomes progressively smoother with increased silanization. Subsequently, this study assessed the stability and extent of surface modifications in silanized samples caused by adsorbed water during storage, using untreated glass beads as a reference. Untreated samples exhibit increased surface roughness and polar groups, causing marginal increase in surface energy and hydrophilicity. In contrast, the silanized samples show resistance to water adsorption, with only minor alterations in surface energy and structure, likely occurring in areas where the silanization coating was incomplete. The results suggest that humidity control is crucial during extended storage, as prolonged moisture exposure could still lead to surface modifications that alter adhesion forces to fluids, even in silanized samples, potentially affecting wettability consistency in repeated experiments.