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A new type of composite hydrophobic/hydrophilic porous membrane is proposed for application in membrane distillation. The membranes were prepared by the phase inversion technique in a single casting step from polymer solutions containing surface-modifying macromolecules. Polyetherimide was used as a hydrophilic base polymer. The effects of polyetherimide concentration in the casting solution on the permeate flux and on the membrane characteristics were investigated. The liquid entry pressure of water, mean pore size, effective porosity and mean roughness of the membranes were determined. Direct contact membrane distillation experiments were performed for pure water and aqueous solutions of sodium chloride as feed. The effect of the mean temperature, stirring rate and salt concentration were studied. Similar experiments were carried out for two commercial polytetrafluoroethylene membranes of …