The Membrane Surface Science group participates actively in the teaching of the Chemical Engineering curriculum, both in the BSc and the MSc phase. The following are the courses offered and their details:
- 193735000 - C.S. Membrane Technology
- 201200117 - Membranes for Gas Separation
- 201300049 – Advanced Molecular Separations
Many different BSc and MSc project are possible within the MSuS group. Projects can involve making or coating membranes (Material Science), but can also be more focused on characterizing membranes and optimizing their performance for a specific application (Process Technology). For a most up-to-date overview of possible projects please contact firstname.lastname@example.org.
Some examples of possible projects are given below:
- Switching the odd-even effect in polyelectrolyte multilayer membranes
Esra te Brinke (1), Wiebe de Vos (1)
(1)Membrane Surface Science (MSuS), Membrane Science and Technology Cluster
Polyelectrolyte multilayer (PEM) membranes, formed by alternate adsorption of polycation and polyanion nanolayers on a membrane support, are recently becoming more and more important in membrane applications. One intrinsic feature of PEM membranes is that they have different properties depending on the terminating layer, the so-called odd-even effect. Not only the polarity of the membrane surface is determined by the terminating layer, but typically also the total charge density and therefore the swelling of the layer . Therefore, besides ion retention also water permeability of the membrane is influenced by this odd-even effect, as well as the molecular weight cut-off of neutral molecules. This effect is very well visible as a zig-zag pattern in membrane permeability as a function of the number of coated polyelectrolyte layers (figure 1). In our lab, we have observed that the odd-even effect can switch depending on coating conditions, i.e. that the coating conditions can determine which of the two polyelectrolytes of a given polyelectrolyte pair will induce most swelling as the terminating layer. However, we do not understand yet what exactly causes this switching. For a better fundamental understanding of PEM membrane production and properties, we want to investigate this.
Figure 1. Odd-even effect on the water permeability when alternatingly coating poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) layers .
The aim of this student project is to find out which parameters determine which polyelectrolyte of a polyelectrolyte pair induces most swelling as a terminating layer. Examples of parameters that might influence the odd-even effect are salt type and concentration in the coating solution, or polyelectrolyte molecular weight. Permeability and molecular weight cut-off will be determined by crossflow experiments and GPC. Additionally, we want to investigate how these parameters affect the odd-even effect. To this extent, PEM buildup will be studied by reflectrometry and if necessary ellipsometry. Initially single polyelectrolyte pair will be investigated, but depending on the duration of the project this can be done for additional polyelectrolyte pairs or for example asymmetric PEM layers to further optimize organic micropollutant retention . Micropollutant retention can be determined by crossflow experiments in combination with HPLC or HPLC-MS.
 J. de Grooth; A tale of two charges: Zwitterionic Polyelectrolyte Multilayer Membranes; doctoral thesis, Ipskamp printing Enschede, 2015
 E. te Brinke, D. M. Reurink, I. Achterhuis, J. de Grooth and W. M. de Vos; Asymmetric polyelectrolyte multilayer membranes with ultrathin separation layers for highly efficient micropollutant removal; Applied Ma
- Crosslinking for further improvement of asymmetric polyelectrolyte multilayer membranes
Esra te Brinke (1), Wiebe de Vos (1)
(1)Membrane Surface Science (MSuS), Membrane Science and Technology Cluster
Membrane performance is not only determined by selectivity but also permeability, which determines the efficiency of the membrane. Permeability can be increased by decreasing the thickness of the selective layer. This idea led to the development of membranes that consist of a porous support for mechanical stability with a thin separation layer coated on top of the support. Layer-by-layer coating of oppositely charged polyelectrolytes, to form a polyelectrolyte multilayer (PEM) membrane, is one of the techniques that can be used for this purpose. However, in practice the coating will also partly fill the support pores which makes the separation layer still much thicker than necessary (figure 1). Recently, this problem was largely circumvented by coating asymmetric PEM membranes with a very permeable bottom layer (poly(styrene sulfonate) + poly(allylamine hydrochloride)) to close the pores, and a 4 nm thin, very dense PEM (poly(acrylic acid) + poly(allylamine hydrochloride)) on top of this as the separation layer . This led to much higher water permeabilities compared with PEM membranes that are completely coated with the dense PEM, and 98% retention of organic micropollutants such as medicines and pesticides. However, further investigation showed that the bottom and top layer are mixed to some extent . This probably leads to a decrease in top layer density, such that the separation properties of the top layer are not yet fully exploited in these asymmetric membranes.
Figure 1. Dense vs. asymmetric PEM coating on a porous support membrane.
The aim of this student project is to covalently crosslink the bottom PEM of the asymmetric membranes with glutaraldehyde before coating the top layer, to inhibit mixing of the bottom and top layer. Crosslinking, however, also has its drawbacks: it densifies the PEM such that overall permeability will decrease, and it reduces the charge of the bottom layer which can affect the properties of the top layer. Therefore, the glutaraldehyde concentration and the crosslinking time need to be finetuned. The effect of crosslinking on the coating process of the top layer will be monitored by reflectometry and ellipsometry. Membrane performance will be determined by crossflow experiments, in combination with analytical techniques such as conductivity measurements, HPLC, HPLC-MS and GPC. Depending on the duration of the project it is also possible to investigate different bottom layer types or different crosslinking agents, or to perform additional crosslinking of the top layer to make it even thinner and denser.
 E. te Brinke, D. M. Reurink, I. Achterhuis, J. de Grooth and W. M. de Vos; Asymmetric polyelectrolyte multilayer membranes with ultrathin separation layers for highly efficient micropollutant removal; Applied Materials Today, 2020, 18:100471
 I. J. Gresham, D. M. Reurink, S. W. Prescott, A. R. J. Nelson, W. M. de Vos and J. D. Willott; Structure and Hydration of Asymmetric Polyelectrolyte Multilayers as Studied by Neutron Reflectometry: Connecting Multilayer Structure to Superior Membrane Performance; Macromolecules, 2020, 53: 10644-54
- Polyelectrolyte based gas barrier coatings for flexible packaging
Jiaying Li (1), Wiebe M. de Vos (1)
(1) Membrane Surface Science (MSuS)
Solvent-borne coatings with a relatively high content of Volatile Organic Compounds (VOCs) have traditionally dominated the coating industry, however, there are increasing health and safety concerns. A transition from solvent-borne coatings to more environmentally friendly coatings has been realized for consumer coatings in the late 1990s.1 Waterborne coating is one of the solutions and has gained enormous research attention in the modern coating industry. Key components of a waterborne coating are water, co-solvent, polymer binder, pigment, and various additives.2 Among all these ingredients, the primary properties of the coating film are determined by the binder.
To explore new possibilities, a new film formation system based on polyelectrolyte (PE) complexation is investigated. PEs are polymers with charged functional groups and usually have good water solubility. With a pH and salt control, the direct complexation is prevented and a homogenous solution mixture can be obtained. The mixture can then be cast onto a substrate with controlled thickness. Upon drying, complexation may occur due to a change in pH by an aqueous bath or evaporation. The possible routes are shown in Figure 1. A strong ionic network among PEs can be formed. Barrier properties and sufficient mechanical strength are expected to be achieved with cross-linking.
Figure 1: Two different routes of complexation
Project details and outcome
In this master project, the main goal is to study different ratios of polycation: polyanion as gas barrier materials. You will start to prepare high concentration of polycation: polyanion solutions in different ratios to understand how that influences the complexation. Different ratios lead to different degrees of ionic cross linking that define the final gas barrier performance. To better understand the microstructure, you will study the intrinsic complex properties by several techniques such as DSC and ellipsometry. During the film preparation, you will also get hands-on experience of different film characterization techniques, for example, SEM and AFM. Moreover you will learn how to perform gas permeation tests. Throughout the whole project, you will learn about water-based coating, polyelectrolyte complexation and gas permeation. Meanwhile, a link between academic research and industrial application is also made, as this project is in collaboration with BASF and AkzoNobel.
In this project, your main tasks are:
1. Preparation of PE solutions
2. Preparation of PE films on substrates
3. Characterizations of the PE films
4. Gas permeation measurements of the PE films
For more details and questions, please contact J. (Lily )Li, email@example.com.
 K. D. Weiss, Paint and coatings: A mature industry in transition. Progress in Polymer Science 22, 203-245 (1997).
 E. Mehravar, J. Leswin, B. Reck, J. R. Leiza, J. M. Asua, Waterborne paints containing nano-sized crystalline domains formed by comb-like polymers. Progress in Organic Coatings 106, 11-19 (2017).
- Membranes by Aqueous Phase Separation (APS): Effect of polyelectrolyte molecular weights on the membrane properties
Muhammad Irshad Baig(1), Wiebe M. de Vos(1)
(1)Membrane Surface Science, Membrane Science and Technology Cluster, MESA+ Institute for Nanotechnology, University of Twente, Faculty of Science and Technology, P.O. Box 217, 7500 AE, Enschede, The Netherlands.
A membrane is a barrier that regulates the flow of species in a selective way. The most commonly used membranes in water purification and gas separation applications are made from polymers that are only soluble in organic solvents. Ask anyone who works in the field of polymeric membranes about its fabrication procedure, and you will mostly hear one answer i.e. NIPS. It stands for Non-solvent Induced Phase Separation. Simply put, you take a polymer (Polysulfone, Polyimides for example) and dissolve it in an organic solvent such as N-methyl-2-pyrrolidone (NMP). When the solution is homogeneously mixed, it is then cast on a flat surface and put in a water bath. The solvent (NMP) is highly miscible in water and so it diffuses out of the polymer solution and mixes with water. The polymer, at this point becomes insoluble due to all the water that is around it, forming a solid porous membrane. The membranes prepared in this way are also known as ‘Loeb-Sourirajan Membranes (L-S membranes)’, named after the researchers who first made asymmetric cellulose acetate membranes for sea water desalination.
Figure 1. Schematic illustration of the polyelectrolyte complex membrane formation.
This simple procedure of making commercial polymer membranes has remained the same since the 1970’s. NMP is by far the most widely used solvent to prepare membranes and the multi-billion dollars membrane industry uses this solvent in immense amounts.
However, NMP is not a friendly chemical by any means. It is partly flammable, and most importantly, it has been proven to be repro-toxic to humans and harmful for the environment.1 Therefore, it has to be recycled and/or removed from waste streams plus it has to be removed from the membranes before they can be utilized for water production. The EU has introduced a law that restricts the use of such chemicals throughout the Union.2
aving discussed the nature of aprotic, polar organic solvents and their harmful effects, we have an alternative solution which uses only water as a solvent. It is extremely difficult and mostly impossible to dissolve conventional polymers in water. This leaves us with a special class of polymers called ‘Polyelectrolytes’ which can be easily dissolved in water. These polyelectrolytes are charged polymers with a unique property that their charge can be manipulated by a pH switch. Some polyelectrolytes are only charged below a particular pH. They are called weak polyelectrolytes. On the other hand, certain polyelectrolytes remain charged in almost all the pH range. These are called strong polyelectrolytes. When the two oppositely charged polyelectrolytes come across each other, they instantly form a ‘Polyelectrolyte Complex’. So if we make a homogeneous solution of these two polyelectrolytes such that they are uncharged in the solution and then cast it in a water bath with a pH where both become charged, we get a polyelectrolyte complex membrane (Figure 1). This novel approach to making membranes is termed ‘Aqueous Phase Separation’ (APS).
Project Details and Outcome
Project Details and Outcome
In this project, Poly(sodium 4-styrenesulfonate) and Polyethyleneimine will be used the polyelectrolytes, respectively. The aim of this project is to develop free-standing membranes using the two polyelectrolytes mentioned above. During the course of the project, Monomer mixing ratio, effect of coagulation bath pH, cross-linking conditions, and type of salt in coagulation bath would be investigated in detail.
The membranes prepared in this study will be used for water treatment and purification applications. The applications are as diverse as the new APS field itself. From oil/water separation (Microfiltration) to sea water desalination (nanofiltration and reverse osmosis), the outcomes of this study are diverse. It is noteworthy that one of the inventors of L-S membranes, Loeb Sidney, was a MSc. student at UCLA when he got the breakthrough in membrane science and technology. Similarly, this project, part of a larger research goal, will play an important role in shaping the next generation of polyelectrolyte membranes.
- D. Prat, J. Hayler and A. Wells, Green Chem., 2014, 16, 4546–4551.
- The European Commission, Off. J. Eur. Union, 2018, 99, 3
- Influence of Ion Concentration on Polyelectrolyte Multilayer based Nanofiltration Membrane Performance
Influence of Ion Concentration on Polyelectrolyte Multilayer based Nanofiltration Membrane Performance (MSc assignment)
In recent years a variety of micropollutants have been detected in ground- and surface water . Micropollutants are small organic molecules with variable chemical properties that originate among others from industrial, medical and agricultural waste. Many of these molecules are highly toxic, carcinogenic or endocrine-disrupting compounds . Even though the observed concentrations are still below drinking water guidelines, these micropollutants are potentially harmful to humans, organisms and the environment, as there is very little knowledge on longtime exposure and possible synergetic effects . Traditional water treatment methods are not able to sufficiently remove these, therefore advanced separation technologies need to be developed to prevent them from accumulating in our water cycle .
Dense membranes used in pressure-driven filtration processes such as reverse osmosis (RO) or nanofiltration (NF) are promising techniques that have been shown to retain most micropollutants . The advantage of nanofiltration membranes over reverse osmosis membranes is the reduced energy cost due to lower pressures at very comparable separation performances. A relatively young and promising method to make nanofiltration membranes is to coat a very thin and selective separation layer on top of an open porous support structure using the Layer-by-Layer (LBL) method, developed by Decher in 1997 . In this method polyelectrolytes of different charged are alternately coated on top of a charged substrate. The layer formation is driven by electrostatic interactions between the polyelectrolyte chains and the entropic gain of counterion release.
Project details and outcome
In the cluster of Membrane Science and Technology these so-called Polyelectrolyte Multilayer (PEM) membranes are developed and investigated. Depending on the membrane coating conditions the structure and with that the membrane performance, solute selectivity and solvent permeability can be changed. At the same time, it is hypothesized, that the membrane performance directly depends on the type and concentration of ions present during filtration. In addition to ion adsorption and charge screening effects, commonly observed phenomena for nanofiltration, the PEM structure might change significantly for different ions and ion concentrations, which has been recently observed in QCM-D studies of PEM swelling behavior .
The aim of this research is to investigate the influence of ion concentration on PEM performance related to structural changes. The focus will be on macroscopic transport measurements conducted with coated ultrafiltration membranes. Simultaneously structural characteristics of the multilayer, coated on a model surface, will be investigated. Following these detailed experimental studies, the applicability of a nanofiltration model based on the extended Nernst-Planck equation for the prediction of membrane retention accounting for ion adsorption, charge screening and structural changes shall be investigated.
· prepare and characterize PEM hollow fiber membranes
· conduct macroscopic transport measurements
· investigate swelling properties for different salts and salt concentrations
· apply a transport model to describe membrane performance
For more information please contact Moritz Junker (firstname.lastname@example.org)
1.Aa, N. G. F. M. v. d.; Dijkman, E.; Bijlsma, L.; Emke, E.; Ven, B. M. v. d.; Nuijs, A. L. N. v.; Voogt, P. d., Drugs of Abuse and Tranquilizers in Dutch Surface Waters, Drinking Water and Wastewater - Results of Screening Monitoring 2009. National Institute for Public Health and the Environment 2010.
2.Trapido, M.; Epold, I.; Bolobajev, J.; Dulova, N., Emerging micropollutants in water/wastewater: growing demand on removal technologies. Environmental science and pollution research international 2014, 21 (21), 12217–12222.
3.Verliefde, A.; Cornelissen, E.; Amy, G.; van der Bruggen, B.; van Dijk, H., Priority organic micropollutants in water sources in Flanders and the Netherlands and assessment of removal possibilities with nanofiltration. Environmental pollution (Barking, Essex : 1987) 2007, 146 (1), 281–289.
4.Tröger, R.; Klöckner, P.; Ahrens, L.; Wiberg, K., Micropollutants in drinking water from source to tap - Method development and application of a multiresidue screening method. Science of The Total Environment 2018, 627, 1404–1432.
5.Yangali-Quintanilla, V.; Maeng, S. K.; Fujioka, T.; Kennedy, M.; Amy, G., Proposing nanofiltration as acceptable barrier for organic contaminants in water reuse. Journal of Membrane Science 2010, 362 (1), 334-345.
6.Decher, G., Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites. Science 1997, 277 (5330), 1232–1237.
7.O’Neal, J. T.; Dai, E. Y.; Zhang, Y.; Clark, K. B.; Wilcox, K. G.; George, I. M.; Ramasamy, N. E.; Enriquez, D.; Batys, P.; Sammalkorpi, M.; Lutkenhaus, J. L., QCM-D Investigation of Swelling Behavior of Layer-by-Layer Thin Films upon Exposure to Monovalent Ions. Langmuir 2018, 34 (3), 999-1009.