Imaging and characterization of reverse osmosis polyamide membranes
File(s)
Author(s)
Li, Yuqiong
Type
Thesis
Abstract
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.
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.
Version
Open Access
Date Issued
2016-11
Date Awarded
2017-05
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
License URL
Advisor
Livingston, Andrew
Cabral, Joao
Sponsor
British Petroleum Company - International Centre for Advanced Materials
Grant Number
ROMSAF
Publisher Department
Chemical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)