Surface segregation of fluorinated modifying macromolecule for hydrophobic/hydrophilic membrane preparation and application in air gap and direct contact membrane distillation

A fluorinated surface modifying macromolecule (SMM) was synthesized and blended into the casting solution of polyetherimide used as host polymer. A composite porous hydrophobic/hydrophilic membrane was prepared by the phase inversion technique in a single casting step. The membrane was characterized by different techniques. During membrane formation, SMM migrates to the top membrane surface increasing its hydrophobicity and decreasing its pore size, nodule size and roughness parameters. The thickness of the porous hydrophobic top layer was found to be around 4 μm. The membrane was used for desalination by air gap membrane distillation and direct contact membrane distillation. The experiments were performed for different sodium chloride aqueous solutions and various operating conditions. The water production rate was found to be high for direct contact membrane distillation because of the low resistance to mass transport achieved by the diminution of the water vapour transport path length through the hydrophobic thin top-layer of the membrane.