Advanced characterization of polyamide thin-films for reverse osmosis membranes
Open Access
- Author:
- Culp, Tyler
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 06, 2019
- Committee Members:
- Enrique Daniel Gomez, Dissertation Advisor/Co-Advisor
Enrique Daniel Gomez, Committee Chair/Co-Chair
Andrew Zydney, Committee Member
Manish Kumar, Committee Member
Robert John Hickey, III, Outside Member
Phillip E Savage, Program Head/Chair - Keywords:
- desalination
reverse osmosis
polyamide
transmission electron microscopy
membrane - Abstract:
- Water availability is an increasingly growing challenge as global economic and population growth place significant stress on current freshwater resources. As such, water purification and desalination technologies, in particular reverse osmosis (RO), are becoming more important due to their high salt rejection, water flux, and energy efficiency. This dissertation aims to provide a better understanding of how the complex, heterogeneous morphology of fully-aromatic polyamide thin-films, which serve as the active layer of RO membranes, influence membrane transport properties. The presented results can be used in the development of future membrane materials with improved water flux and salt rejection. The first step to improving our understanding transport mechanisms in polyamide RO membranes is through quantitative characterization. This first portion of this dissertation details how that can be accomplished by obtaining 3D models of the polyamide active layer with transmission electron microscopy (TEM), where key membrane properties relevant to transport can be accurately measured. From here, we can use the polyamide models to quantify the 3D nanoscale heterogeneity in polymer mass. These nanoscale variations in mass result in polyamide density, fractional free volume, and diffusion coefficient of water distributions. By combining the 3D models and density distributions, we can simulate water transport through polyamide films, allowing for the quantification of the effect of nanoscale polyamide heterogeneity on water transport. Further, this dissertation demonstrates the application of resonant soft X-ray scattering to polyamide films, where the influence of polyamide chemistry on morphology can be evaluated. Through a combination of soft X-ray scattering contrast calculations, atomic force micrographs and TEM micrographs, we can assign the dominant contributions to scattering profiles as either surface roughness or chemical heterogeneity. These results demonstrate the utility of soft X-ray scattering for analyzing the microstructure in polyamide films.