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Title: Imaging and characterization of reverse osmosis polyamide membranes
Author: Li, Yuqiong
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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This work is part of a British Petroleum-International Center for Advanced Materials (BP- ICAM) project titled "Reverse Osmosis Membranes: Structure and Functions" (ROMSAF), which seeks theoretical, structural and functional understanding of RO membranes for seawater desalination processes. In the present study, the focus is on the molecular-level understanding of the structure of polyamide (PA) thin film composite (TFC) RO membranes. In this thesis, an imaging protocol has been established for analysis of both surface and cross- sectional views of polymeric membranes with ultra-microtome, high-resolution electron microscope (EM), and 3-dimensional (3D) EM tomogram techniques, with the addition of nanoparticle imaging agents (NIAs) for contrast enhancement and infiltration into membranes under pressurized operating conditions, which enabled revelation of permeation pathways in operando. Techniques other than EM real space imaging, such as atomic force microscope (AFM), were used to complement EM techniques for ambient condition measurements. Scattering methods, such as X-ray photoelectron spectroscopy (XPS) were employed to study the thickness of dense PA network in the active layers. Other analytical tools explored included elemental analysis using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), mathematical modeling of surface roughness using 2D-power spectral density (PSD) and fractal dimension calculations, as well as atomistic representation. In addition to structural imaging of RO membranes, this work also prompted re-thinking of separation resolution of nanofiltration (NF) membranes, which depends on resistance to solute transport along the permeation channels, manifesting steric hindrance and hydrodynamic friction, and the implications of hindrance effect on NIA-aided imagings. Based on the improved spatial-temporal understanding of RO and NF transport down to molecular level, this study seeks to design and guide the fabrication of high performance membranes with tunable geometries and chemistry that will in turn effect high selectivity and flux throughput.
Supervisor: Livingston, Andrew ; Cabral, Joao Sponsor: International Centre for Advanced Materials, British Petroleum Company
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral