| Summary: | The structural (<i>S</i>) parameter of a medium is used to represent the mass transport resistance of an asymmetric membrane. In this study, we aimed to fabricate a membrane sublayer using a novel composition to improve the <i>S</i> parameter for enhanced forward osmosis (FO). Thin film composite (TFC) membranes using polyamide (PA) as an active layer and different polysulfone:polyethersulfone (PSf:PES) supports as sublayers were prepared via the phase inversion technique, followed by interfacial polymerization. The membrane made with a PSf:PES ratio of 2:3 was observed to have the lowest contact angle (CA) with the highest overall porosity. It also had the highest water permeability (<i>A</i>; 3.79 ± 1.06 L m<sup>−2</sup> h<sup>−1</sup> bar<sup>−1</sup>) and salt permeability (<i>B</i>; 8.42 ± 2.34 g m<sup>−2</sup> h<sup>−1</sup>), as well as a good NaCl rejection rate of 74%. An increase in porosity at elevated temperatures from 30 to 40 °C decreased <i>S<sub>int</sub></i> from 184 ± 4 to 159 ± 2 μm. At elevated temperatures, significant increases in the water flux from 13.81 to 42.86 L m<sup>−2</sup> h<sup>−1</sup> and reverse salt flux (RSF) from 12.74 to 460 g m<sup>−2</sup> h<sup>−1</sup> occur, reducing <i>S<sub>eff</sub></i> from 152 ± 26 to 120 ± 14 μm. <i>S<sub>int</sub></i> is a temperature-dependent parameter, whereas <i>S<sub>eff</sub></i> can only be reduced in a high-water- permeability membrane at elevated temperatures.
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