Thin film composite (TFC) osmotic membranes based on polyacrylonitrile (PAN) and polyamide were prepared for FO applications. The selective properties were optimized by fine tuning preparation parameters in the interfacial polymerization process, such as the composition of the reactant monomer mixture, reaction time, and air drying period. The results revealed two key parameters to have a significant influence on the selective layer properties: the surfactant additive and the drying period of the excess amine solution on the support surface before contacting with the second reagent. With the addition of the surfactant (sodium dodecylsulphate, SDS), the salt retention increased from 56.8% to 95.6% without loss in water permeance. The proper removal of the excess amine solution resulted in smoother membrane surfaces with an extra salt retention improvement from 84.2% to 94.5%. In addition, the optimal conditions to prepare an RO-like selective skin deposited on a PAN support were established. The optimal membrane obtained from this work exhibited superior FO performance compared to the commercial HTI membranes. (c) 2013 Elsevier B.V. All rights reserved.