Interfacial Water-Dictated Oil Adhesion Based on Ion Modulation

Oil adhesion on ionic surfaces is ubiquitous in organisms and natural environments and is generally determined by surface chemical component and texture. However, when adhesion occurs, water molecules at the solid–liquid interface, acting as a bridge not only influenced by the structure and composition of the solid surface but also interacting with the neighboring oil molecules, play a crucial role but are always overlooked. Herein, we investigate the oil adhesion process on a carboxyl-terminated self-assembled monolayer surface (COOH-SAM) in ionic solutions and observe the interfacial water structure via surface-enhanced Raman scattering (SERS) in this system. It is found that the lower the tetracoordinated water content, the stronger the oil adhesion. Compared to monovalent ions, the strengthened binding of multivalent ions to the COOH-SAM surface makes the interfacial water more disordered, which eventually leads to a stronger oil adhesion. Notably, the amount of oil adhesion decreases with an increase in the thickness of the interfacial water region. The interfacial water-dictated oil adhesion has been demonstrated in capillary to simulate the water-driven oil recovery, providing a molecular-level explanation for enhanced oil recovery from low salinity water flooding and also indicating potential applications in intelligent microfluidic and seawater desalination.