Polyelectrolyte multilayer nanofiltration membranes: Advancing insights towards asymmetric multilayers

Within this work, we have aimed to obtain a more complete overview on how specific parameters influence both symmetric and asymmetric polyelectrolyte multilayer (PEM) nanofiltration (NF) membranes. Here, the focus was on obtaining more knowledge and understanding on the connection between multilayer build-up and the subsequent performance of the formed PEMMs. This has been achieved by investigating a broad spectrum of PEs and parameters, and a fair comparison of membrane performance.
Chapter 1 provides the motivation for this work as well as background information on membrane separation and polyelectrolyte multilayers. Chapter 2 presents an experimental review of a broad range of polyelectrolytes showing that PEMM performance can be connected to PEM properties. Also, it becomes apparent that swelling is one of the key parameters in PEMM performance. Chapter 3 investigates the influence of molecular weight on the performance of PEMMs. We show that more mobile PEMs are affected to a larger extend using different Mw compared to PEMs that have low mobility. Chapter 4 investigates further into the concept of asymmetric PEMMs. The effect of applying different types of top sections and varying bottom section thickness is explored regarding final membrane performance. We show that it is possible to uncouple charged and uncharged solute retention till the point that defects are forming. Chapter 5 focusses on the influence of pH during operation of PEMMs. As expected, strong PEs are almost not affected upon pH change. However, a combination of weak polyelectrolytes shows to be very susceptible to pH changes resulting in structural and performance changes. Chapter 6 concludes on all chapters, provides a complete summary of the performed work and gives an outlook for future research.