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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 4μm. 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 …