Formation of hydrophobic membranes by surface spray assisted NIPS: Effects of solvent/non-solvent and spraying conditions

Membrane distillation has long been a potential desalination technology. Recently, spray-assisted non-solvent induced phase inversion (SANIPS) was proposed as a facile and effective method to prepare microporous hydrophobic membranes for membrane distillation. However, the membrane formation process is not fully disclosed. In this paper, SANIPS is employed to fabricate hydrophobic PVDF membranes. The influencing factors on membrane structure and performance are investigated. Membrane structure is greatly affected by the choice of solvent and non-solvent spray. The interactions between different non-solvent sprays (water and ethanol) and solvents (TEP, NMP and DMF) and the effects of operating conditions on membrane formation are explored. Thermodynamic and kinetic analyses of the membrane formation process suggest that the membrane formation process is dominated by the kinetic factors with water being the spray while thermodynamic factors play the major role with ethanol being the spray. A hydrophobic membrane with water contact angle of 135.93 ± 4.38° and LEP of 2.5 ± 0.4 bar was successfully prepared by using ethanol as the non-solvent spray, which demonstrates a stable desalination performance (initial flux of 19.88 ± 1.39 kg·m⁻²·h⁻¹ and salt rejection higher than 99.97 %) in vacuum membrane distillation. This study may provide pertinent insights into the rational control of membrane structure and performance of hydrophobic PVDF membranes.