Salt-Responsive Wettability Alteration of Gold Nanocomposites: Experimental and Molecular Dynamics Studies

Wettability alteration is of significant importance and practicality in daily life, including waterproofing, self-cleaning, and reducing flow resistance. To investigate the mechanism of wettability transition at the interface, this study presented a salt-responsive intelligent nanofluid (G@(MO)-NPs), modified with gold nanoparticles (GNPs), capable of regulating wettability transformation through NaCl stimulation. Uniform-sized GNPs, with an average diameter of approximately 10 nm, were synthesized via the sodium citrate reduction method. A nanocomposite material exhibiting salt responsiveness was then constructed by grafting the random copolymer MEO₂MA-co-OEGMA (RPMCO) onto the GNPs. The findings demonstrated that G@(MO)-NPs migrated from the aqueous phase to the oil phase (n-decane) due to salt-ion addition, notably weakening the hydrogen-bond interactions. This change resulted in wettability alteration and directional self-assembly of the nanocomposite at the oil-water interface. This intelligent nanofluid system offers a novel approach for the wettability alteration of the oil displacement agent and demonstrates significant industrial application potential. However, the practical application may be challenged by factors such as the cost of gold nanoparticles, long-term environmental impact, and performance under high-pressure-high-temperature (HPHT) conditions, which warrant further investigation.