Molecular Structure of Aromatic Reverse Osmosis Polyamide Barrier Layers

Abstract

The molecular structures of polyamide barrier layers in reverse osmosis membranes, made by interfacial polymerization of m-phenylenediamine and trimesoyl chloride under different reaction and post-treatment conditions, were characterized by grazing incidence wide-angle X-ray scattering (GIWAXS). The molecular backbone packing is consistent with two different aromatic molecular packing motifs (parallel and perpendicular) with preferential surface-induced orientation. The results suggest that the perpendicular, T-shaped, packing motif (5 Å spacing) might be associated with optimal membrane permeance, compared with the parallel packings (3.5–4.0 Å spacings).

Fabrication of desalination membranes by interfacial polymerization: history, current efforts, and future directions

“…9C), where intense scattering is preferentially aligned along the vertical q z direction, implies the in-plane orientation of aromatic stacking in the polyamide film. 59 Further analysis of this WAXS pattern by plotting the scattered intensity versus scattering vector, q, suggests the presence of two peaks centered at 1.79 Å À1 and 1.22 Å À1 . According to Bragg's law (d = 2p/q), these two peaks correspond to molecular spacings of 3.5 and 5.2 Å, respectively.…”

“…9). [59][60][61] During the measurements, the incident sources (e.g., X-ray or neutron) are scattered by the electrons (X-ray) or the nuclei (neutron) to generate corresponding signals (Fig. 9A).…”

“…9B), incident X-ray is shed on a polyamide film at a relatively small angle, and scattered signals are then detected by a 2D detector. 59 As the film is horizontally positioned on a sample stage, analysis of scattering patterns could provide information on both molecular structure and preferential orientation (either in-plane or out-of-plane) of the polyamide network. 59 For example, an arc-like meridional scattering feature in a WAXS pattern (Fig.…”

“…59 As the film is horizontally positioned on a sample stage, analysis of scattering patterns could provide information on both molecular structure and preferential orientation (either in-plane or out-of-plane) of the polyamide network. 59 For example, an arc-like meridional scattering feature in a WAXS pattern (Fig. 9C), where intense scattering is preferentially aligned along the vertical q z direction, implies the in-plane orientation of aromatic stacking in the polyamide film.…”

New Insights into Water Treatment Materials with Chemically Sensitive Soft and Tender X-rays

“…Understanding and controlling membrane morphology based on polymer chemistry and processing conditions is required for next-generation materials. Important insights into the morphology of water treatment membranes have been achieved through characterization tools, including electron microscopy [12][13][14], neutron scattering [15][16][17], and hard Xray scattering [18,19]. Figure 1a [22].…”