Title: Probing free volume property of polyamide thin film composites with different cross-linking densities
Abstract: Two commercial polyamide thin film composites (labelled AG and AK) with different polyamide (PA) cross-linking densities were examined for morphology, chemical structure, Doppler broadening positron annihilation spectroscopy, and salt desalination performance.The highly cross-linked AG sample resulted in higher salt rejection but slightly lower water permeance.Meanwhile the highly cross-linked sample showed smaller S parameters than the loosely cross-linked one.The highly cross-linked PA structure resulted in a higher salt rejection and lower water permeation rate.The free volume behavior resulting from various cross-linking densities is captured using the Doppler broadening annihilation spectroscopy.