The charge regulation of surfactants on the rock surface in nanoconfinement: A reaction-coupling fluid density functional theory study

•Joint fluid DFT and surface reaction model could accurately predict surface charge density and ζ potential of rock.•The pore size effect became negligible with the increasing surfactant concentration.•The upper limit of charge regulation performance emerges as the surfactant concentration increases.•The ζ potential exhibits less negative with the increasing surfactant concentration due to the electrostatic screening.•The chain length effect is significant in cationic surfactants systems, while anionic surfactants’ behavior is similar to simple salt.