A series of thin-film composite (TFC) polyamide membranes was fabricated through interfacial polymerization on a modified polyacrylonitrile (mPAN) substrate, where an aqueous solution of diamine was reacted with an organic solution of diacyl chloride. Various monomers were used: two different diamines [1,3-diamino-2-propanol (DAPL) and hydrazine] and two different diacyl chlorides [succinyl chloride (SCC) and trans-5-norbornene-2,3-dicarbonyl chloride]. Combining these monomers resulted in a new polyamide layer. We investigated the effect of the monomer chemical structure and interfacial polymerization conditions on the membrane pervaporation performance in dehydrating an aqueous solution of ethanol. According to field emission scanning electron microscopy, DAPL-SCC provided the thinnest polyamide layer, which was also confirmed through positron annihilation lifetime spectroscopy. The results were used to correlate the variation in the membrane microstructure with the pervaporation performance of the fabricated TFC polyamide membranes. Both microstructural characteristics and surface properties affected the pervaporation performance. DAPL-SCC/mPAN membranes with lower free-volume sizes and suitable hydrophilicity were evaluated to deliver the highest water concentration in permeate and the lowest permeation flux (on the basis of the pervaporative dehydration of an aqueous solution of 90 wt% ethanol at 25 degrees C).