Quantitatively probing interactions between membrane with adaptable wettability and oil phase in oil/water separation

The membrane method based on adaptive wettability shows great advantages in oil-water separation. At present, researches focus on the excellent application performance of the membrane material, while the quantitative analysis of interactions in oil-water separation is rarely recognized. Herein, we constructed an adaptable wettability membrane with multiple polymer networks by polydopamine (PDA) and mussel-inspired amphiphilic polymer. Based on the Owens three-probe liquid method, the surface energy of the modified membrane was verified to meet the adaptive wettability conditions, with surface energies (γS) of 147.6 mJ m−2 (superhydrophilic/underwater superoleophobic) and 49.87 mJ m−2 (superhydrophobic/superoleophobic), respectively. The adhesion or repulsion of the membrane to the oil phase under different conditions during the separation process was quantified by the chemical probe AFM technique. In addition, the oil-water selective separation mechanism was further analyzed in a simplified membrane microchannel model. The results show that the different wetting produces capillary additional pressure in opposite directions, resulting in different energies to be overcome when the oil or water passes through the microchannels, thus achieving selective separation.