Charge-structure synergy in reservoir wettability reversal: Investigating with an integrated optical-multiscale framework

Reservoir wettability modification is a key strategy for enhancing oil recovery (EOR), yet the mechanisms driving this reversal remain incompletely understood due to the scarcity of multiscale characterization methods. In this study, we developed an integrated multiscale framework that combines contact angle measurements, rheological analysis, quartz crystal microbalance with dissipation monitoring (QCM-D), and oblique-incidence reflectivity difference (OIRD) to investigate surfactant-mediated wettability reversal. Our findings reveal distinct charge-dependent pathways: anionic sodium dodecyl sulfate (SDS) promotes monotonic hydrophilization through hydrophobic-driven monolayer adsorption. In contrast, cationic cetyltrimethylammonium bromide (CTAB) exhibits a non-monotonic wettability transition—initially increasing hydrophobicity before sharply reversing to a hydrophilic state. This behavior arises from initial electrostatic adsorption forming hydrophobic monolayers, followed by post-critical micelle concentration (post-CMC) micellar co-adsorption, a process involving interfacial integration and reorganization of surfactant micelles that culminates in bilayer formation and hydrophilic reversal. CTAB’s cationic groups enable strong electrostatic anchoring to negatively charged mica substrates, facilitating dense monolayer-to-bilayer transitions. Conversely, SDS anionic headgroups experience electrostatic repulsion, limiting adsorption to disordered monolayers. This multiscale approach offers critical mechanistic insights for optimizing functional coatings and microfluidic systems via precise wettability control.