Study on the hydrophobic modification of PVDF membrane by low-temperature plasma etching in combination with grafting in supercritical carbon dioxide

Poly (vinylidene fluoride) (PVDF) membrane has good resistance to acid and alkali, chemical stability, high mechanical strength, piezoelectric performance features, especially has good hydrophobic, can be used as blood purification, aerospace flexible sensor pieces, architectural membrane material, water desalination, etc., but for a particular application scenario, the hydrophobic properties still need further improvement. In this study, based on the principle of bionics, low-temperature plasma was used to construct a rough structure and generate active groups on the PVDF membrane surface. Fluorinated monomers were grafted onto the PVDF membrane in supercritical carbon dioxide (scCO2) fluid. The bionic effect of the lotus leaf was constructed on the membrane surface, and the hydrophobicity of the PVDF membrane was significantly improved. The results showed that the rough structure of the PVDF membrane surface was better when the plasma etching conditions were 600W and 300s. When PVDF membrane was swelled for 3h at 35 °C and 13.56 MPa, and grafted for 6h at 100.7°Cand 26.08MPa in scCO2, the PVDF membrane contact angle could reach 140.6°, which was close to superhydrophobic. The hydrophobic reagent was covalently grafted onto the surface of the PVDF membrane by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis. The atomic force microscopy (AFM) test showed that the membrane surface modified by this method had a combination of micro and nanostructure. Further, it confirmed the contribution of a rough surface with low surface energy to water resistance. The processing method meets the requirements of peak carbon emission and net zero carbon dioxide emission, which has important guiding significance for developing hydrophobic surfaces.