Ettore virga graduates with a cum laude!

Details about his work and the defense can be found here:

Ettore defends his PhD thesis

Wouter Nielen successfully defends his PhD thesis

  • Wouter nielen successfully defends his PhD thesis


    Wouter Nielen was a PhD student in the research group Membrane Science & Technology (MST). His supervisor is W.M. de Vos from the Faculty of Science and Technology (S&T).

    His thesis investigates and demonstrates how polymeric membranes can be prepared using the new and more sustainable aqueous phase separation (APS) approach. Polymeric membranes are used on huge scales for kidney dialysis, wastewater treatment, drinking water production, and as a less energy intensive alternative to conventional industrial separation processes. However, the vast majority of polymeric membranes are produced via an unsustainable and environmentally unfriendly process which uses large amounts of reprotoxic chemicals like N‑methyl‑2‑pyrrolidinone (NMP) and dimethylformamide (DMF). Unlike the conventional methods the APS approach uses a water based system using a pH or salinity switch instead of toxic organic solvents to prepare membranes. This allows for a more sustainable membrane production process without the use of reprotoxic solvents. In the past few years three different APS approaches have been established; the first is the single-polyelectrolyte approach, where a responsive polyelectrolyte solution is precipitated by a pH switch. The second and third approach, on the other hand, use a two polyelectrolyte APS system where the complexation of oppositely charged polyelectrolytes forms the membrane either through a pH or a salinity switch. This thesis focusses on the single polyelectrolyte approach and investigates two different polyelectrolytes that can be used in this approach as well as various parameters that can be used to control and tune the membrane preparation.

    In Chapter 1 an introduction to membrane technology and applications is provided along with an overview of parameters used in conventional polymeric membrane preparation, the non-solvent induced phase separation (NIPS) approach. Several alternative methods to prepare polymeric membranes, which use different and less toxic solvents than the conventional NIPS method, are discussed. These methods aim to improve the sustainability of polymeric membrane production but ultimately still rely on organic solvents which the APS approach tries to avoid.

    The preparation of membranes using the pH-responsive polymer poly(4‑vinyl pyridine) (P4VP) is discussed in Chapter 2. P4VP is a polybase and is dissolved at low pH where the polymer is charged and water-soluble, and subsequently casting the solution as a thin film. Switching to a high pH where the polymer becomes uncharged and insoluble results in controlled phase separation and solidification of the polymer into porous membrane structures. By tuning the pH of the coagulation bath and the polymer and acid concentration in the polymer casting solution a large control over the membrane structure is achieved. It was found that by using acetic acid instead of hydrochloric acid in the polymer casting solution the highest control over structure and reproducibility was achieved, most likely due to the weak acid acting as a buffer. By using these tuning parameters both symmetric porous microfiltration membranes and asymmetric dense nanofiltration membranes were prepared. In addition, the pH-responsive nature of P4VP automatically leads to a pH-responsive membrane where the degree of responsive behaviour can be tuned by the degree of crosslinking. This responsive behaviour makes it possible to easily clean the membrane, without using harsh chemicals.

    While good permeability and retentions were achieved with the P4VP membranes, the mechanical stability was found to be suboptimal, as failure of the membranes was observed at an applied pressure of more than 4 bar. To prepare membranes with high mechanical stability using the APS approach the copolymer polystyrene-alt-maleic acid (PSaMA) was used in Chapter 3. PSaMA combines the responsive monomer maleic acid, required for APS, with the unresponsive hydrophobic styrene which enhances the mechanical stability of the resultant membranes. The precipitation of PSaMA can be precisely controlled which allows the preparation of a wide range of membranes, from microfiltration membranes capable of treating oily waste water, to dense nanofiltration-type membrane with excellent micropollutant retentions. As with the P4VP system weak acids again are a key parameter in controlling the precipitation behavior of the polyelectrolyte. Acetic acid is used in the polymer casting solution, where it brings the polymer close to the point of precipitation, as well as in the coagulation bath where it controls the precipitation rate of PSaMA. By tuning the final pH of the coagulation bath MF and UF membranes are prepared and by using phosphoric acid instead of acetic acid in the coagulation bath dense NF membranes. The mechanical stability of the PSaMA membranes is significantly better than the P4VP membrane prepared in Chapter 2 as the membranes presented in this chapter demonstrate stable operation up to 20 bar of applied pressure.

    The phase behavior of polyelectrolytes can be determined by the pH and salinity, but also by the exact nature of the used counter-ions. In Chapter 4 it is investigated how salt type can affect, and thus be used to control, the phase separation of PSaMA. At equal ionic strengths, it is found that Na2SO4 and LiCl lead to the formation of more open structures compared to NaCl, NaNO3, NH4Cl, and MgCl2, while CaCl2 leads to densification of the top layer. These ion-specific effects appear to be caused by a combination of ion mobility and the interaction potential between the ion and the polymer. With increasing salt concentration similar effects are observed for all salt types, the formation of asymmetric membranes with denser top layers. Overall, it is shown that salt identity and concentration are key parameters in the APS process, and can be used to prepare both open microfiltration as well as dense nanofiltration membranes.

    While in Chapter 3 and 4 good membranes have been prepared, large amounts of acetic or phosphoric acid were used in the coagulation baths. To further improve the sustainability of the APS approach it is important to reduce the amounts of acid used and prepare membranes in milder conditions. In Chapter 5 it is demonstrated that it is possible to prepare membranes with PSaMA while only using low concentrations (0.1–0.3 M) of hydrochloric acid in the coagulation bath. Additionally, it is shown that polymer and acetic acid concentration in the polymer casting solution have significant effects on the membrane formation. Polymer concentration in APS behaves the same as in regular NIPS, where an increased concentration leads to denser structures and vice versa. In Chapter 5 this is employed to prevent defect formation in the selective layer of the nanofiltration membranes. Differences in the acetic acid concentration in the polymer casting solution appear to mostly affect the support structure of the membrane where a reduced concentration significantly reduces the formation of macrovoids. Understanding of how these parameters affect membrane preparation and performance is essential to optimizing membranes prepared with APS.

    The membranes prepared with PSaMA are typically chemically cross-linked to prevent the polymer from redissolving at neutral pH conditions. As crosslinking is a common method to make membrane resistant to organic solvents it is of interest to investigate if the standard crosslinking of PSaMA membranes also makes them solvent resistant. In Chapter 6, it is demonstrated that PSaMA membranes have stable performance in both isopropanol (IPA) and toluene, and a slightly reduced performance in N-methyl-2-pyrollidone (NMP). However, PSaMA does not perform well as a selective layer in these solvents, indicating that the real opportunity would be to use the UF type PSaMA membranes as solvent stable support membranes. Additionally, in Chapter 6 the pH stability and responsiveness of PSaMA membranes is also investigated. The membranes are shown to be stable in neutral and acid pH regimes (2–7) and the NF membranes demonstrate a pH dependent retention of Mg2+ and SO42− ions while the UF type membranes show a strong pH responsive behavior in regards to permeability. However, long term exposure to elevated pH conditions (pH 8–10), result in severe swelling of the NF membranes resulting in defect formation, and compaction of the UF membranes. For the UF membranes this compaction was found to be reversible for some but not all of the membrane samples measured. These results show that in aqueous systems membranes prepared with PSaMA have interesting responsive behavior, but perform best at neutral and acidic pH values. Moreover, the membranes exhibited excellent stability in the organic solvents IPA and toluene.

    While the single-polyelectrolyte APS approach is extensively investigated in Chapter 2–6 research is never finished and there is plenty of work left to be done. In Chapter 7 an overview of different avenues to continue the investigation into the single-polyelectrolyte APS approach is provided. This includes a selection of interesting polymers specifically designed for the APS approach which can lead to new and improved membranes. Another important step in development of APS is the preparation of hollow fiber membranes, which offers some distinct advantages over flat sheet membranes, such as reduced fouling and higher packing densities. Initial results are shown which demonstrate that it is possible to prepare hollow fibers using the single-polyelectrolyte APS approach. Additionally, some issues that were encountered concerning the polymer quality are discussed which can have a severe impact on the formation on (defect free) membranes.

    Overall, this thesis showcases the single-polyelectrolyte APS approach, a highly novel sustainable approach to prepare polymeric membranes. The approach offers distinct advantages over conventional membrane preparation methods as it does not rely on reprotoxic solvent. Moreover, it matches the versatility of the conventional methods as it allows for the preparation of both open and dense membranes. The prepared membranes can match commercial available membranes with retention in aqueous environments, have high mechanical stability and are resistant to various organic solvents, while especially the permeability still requires improvement. This thesis marks the beginning of a new method that has the potential to significantly improve the sustainability of the membrane industry.

Elif reviews polyelectrolyte membranes with advanced functionalities in her latest publication

Jiaying's fresh take on sustainable packaging using polyelectrolyte complexation as oxygen barrier coatings:

Want to know a fun way to make transparent saloplastics and use them as a membrane? Check out Ameya's paper:


Ettore Virga wins the Marcel Mulder award 2020. MSUS is proud!

Ettore's research is part of the Concentrates Theme at Wetsus. He has invented a new generation of membranes that can prevent fouling even in the most adverse conditions. A novel zwitterionic polymer has been successfully coated on membranes to make them less prone to fouling. In this way, the industry will use less energy and chemical consumption for water filtration. The coating can be applied to any surface where fouling needs to be avoided, creating an even bigger impact.  

Ettore Virga will graduate within the standard 4 years and already has published 6 papers on his new technology, all in high ranking journals. He is now in charge of coordinating the Concentrates Theme while finishing his Ph.D. research.

in her paper, Elif DURMAZ explains how she used SALINITY CHANGE to induce AQUEOUS PHASE SEPARATION, and in turn fabricate novel Polyelectrolyte Complex Membranes! 



Anna Marie's new review on the 'Recent Developments and Practical Feasibility of Polymer‐Based Antifouling Coatings' is online!

Irshad bags the first prize at NAMS 2020 for his poster!

Muhammad Irshad Baig presented a poster titled “Polyelectrolyte complexation induced Aqueous Phase Separation for the next generation of sustainable membranes” at the North American Membrane Society (NAMS 2020) conference for which he received the Best Poster Award in the ‘Processes’ category.  In this poster, Irshad highlights a new approach to prepare Aqueous  Phase Separation membranes using a combination of strong and weak polyelectrolytes.

HOT OFF THE PRESS! Check out Wouter Nielen's latest article

Wouter's work on 'Aqueous Phase Separation of Responsive Copolymers for Sustainable and Mechanically Stable Membranes' is up for viewing!


the LATEST article by Josh and Wouter is online!

Irshaid Baig's New publication in Advanced Functional materials!

And that's how we celebrated EsRa's Last day at work


Ameya Bysani wins 2nd prize of the David reinhoudt poster award!

David Reinhoudt Poster Award

News off the press! new Papers by Ettore Virga, Janneke Dickhout and Zamidi Ahmad

MSuS Day OUT! Activities, Lots of fun, and great food :)

MSuS Day Out 2019!
The group picture!
Treadmill bike experience :)
The virtual treasure hunt
The winners :)
The five-course dinner, Wiebe's warm words, and a feeling of togetherness!
So close, yet so far!

Golfing in the woods 

The ever-so-happy boss!
Celebrity of the day
  • 5 new masters in Membrane Engineering!

    The MST cluster is proud to announce that on the 12th of July, 5 students successfully defended their MSc thesis. These students are all part of the Erasmus Mundus Master in Membrane Engineering for a Sustainable World (EM3E-4SW), a European MSc program run by 6 universities from 5 European countries. Three of the five students performed their final MSc project within the MSuS group. We congratulate Micah, Fei, Fatima, Jomuel, and Sajjad with their degree and wish them well. In the picture, the five students are with their supervisors. 

Dr. Wiebe de Vos has featured in the crew of eye-openers! Eye-openers is an online stage for talented young scientists. Here they tell about their research, what's it about, what inspires them and what they're dreaming of. In clear language, visually stunning and in one minute only. Click the link below to watch what Wiebe has to say:

MSuS heartily welcomes three new Ph.D. candidates JurjenLily, and Tao to the group!  


  • PhD defense of Jannecke Dickhout


    Janneke Dickhout was a PhD student in the Soft Matter, Fluidics and Interfaces Group. Her supervisor was prof.dr. R.G.H. Lammertink from the Faculty of Science and Technology.

    Produced water (PW) is the largest waste stream from the petrochemical industry (about 3 barrels of PW per barrel of oil). PW is an oil-in-water emulsion containing dispersed and dissolved hydrocarbons, surface-active compounds, solid particles and usually has a high salinity. This complex mixture has to be treated before the water can be disposed or re-used, and membrane treatment is a viable method to achieve this. Membranes, however, suffer from fouling, but the extent to which this results from the many different components in PW and/or from interactions between these many components is poorly understood. This is worrying, as understanding of the causes and mechanisms of membrane fouling, is essential to develop the membrane materials and membrane processes that would allow successful PW treatment.

    The aim of this thesis is to create increased understanding regarding membrane fouling by oil-in-water emulsions.  The adhesion of oil droplets in an emulsion to a model surface was studied visually in a flow cell and compared to membrane filtration experiments using the same emulsion. It was found that the interaction between the salt concentration and surfactant type of the emulsion plays an important role in membrane fouling. Understanding this interaction is key to work towards new and improved membrane applications in challenging feed streams, such as PW.

  • PHD defense of Terica Sinclair

    Terica Sinclair, who worked on "Virus Control by Enhanced Physical Separation", received her Doctorate on the 31st of May, 2018. She was a Ph.D. student in MSuS, in collaboration with Wetsus, and was supervised by H.D.W. Roesink and prof.dr. A.M. de Roda Husman. 

    Her research involved the modification of MF membranes for enhanced pathogen removal for drinking water treatment. By using these modified membranes, drinking water purification processes can be simplified compared to UF based treatment systems, a significant advantage for decentralized water treatment systems. 

    She received the 'Best Ph.D. project' award in June 2017. Details regarding her Ph.D. research can be found here.

  • PhD defense of Timon Rijnaarts

    Timon Rijnaarts successfully defended his Ph.D. on the 3rd of May, 2018. His study which was titled "The role of membranes in the use of natural salinity gradients for Reverse Electrodialysis" was in the MSuS group, in collaboration with Wetsus in Leeuwarden. His research focused on addressing challenges in Reverse Electrodialysis with natural waters. He studied different chemistries and shapes of polymeric membranes and alternative process strategies for Electrodialysis. 

    Since March 2018, Timon is working as a researcher for the European Membrane Institute (EMI), on water-related research.