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Self-Assembled Polymer Membranes

Final Report Summary - SELFMEM (Self-Assembled Polymer Membranes)

The Seventh Framework Programme (FP7) European Union (EU)-cofunded project SELFMEM aims at generation of isoporous membranes based on block copolymer self-assembly and understanding the mechanisms of their formation.

Different routes for their production are investigated:
1) membranes composed of a thin top layer having isoporous channels on top of a spongy support of the same block copolymer on a nonwoven substrate resulting from the so-called phase inversion process;
2) block copolymer thin films are used as an etching mask on silicon substrates, which are then transformed into isoporous membranes.
The block copolymers are synthesised by controlled polymerisation techniques (anionic, group transfer, and different controlled radical polymerisations), depending on the chosen monomers. The aim of the broad synthetic strategy is to find promising candidate materials rather fast. The morphological characterisation is carried out during and after formation of the membranes and is basically performed by different electron microscopic techniques and atomic force microscopy, as well as by various X-ray scattering techniques. Post-functionalisation reactions are applied in order to tailor the properties of the final membranes in a later stage of the project. The membranes have potential applications in different fields. Feasibility studies to separate gases (like H2 / CO2) and proteins as well as water filtration are addressed mainly in the second period of this project. Modelling and theory are in progress and are used to support the understanding of the structure formation of these membranes and to optimise membrane design. Due to the participation of both academic and industrial partners, the close collaborations within the project should accelerate the development of promising membrane concepts for the mentioned applications.

Organisation of SELFMEM

The consortium of the project consists of 8 academic and 4 industrial partners from 10 countries under the coordination of Helmholtz-Zentrum Geesthacht. The project is spanning a bridge between research and development of the isoporous polymeric and inorganic membranes on one side to the demonstration of the developed results on the other side. The achievements will be disseminated by publications in scientific and technical journals, oral and poster contributions at conferences and fairs, as well as by this homepage. These activities are distributed in several, inter-linked work packages (WPs).

Project context and objectives:

The SELFMEM aims to develop new generations of ultrathin nanoporous membranes using the concept of block copolymer self-assembly for the creation of nanopores. This project will generate radical innovation in the membrane community with the production of both organic (polymeric) and inorganic (silicon-based) membranes of controlled porosity and thickness in the nanometer range. Efforts will also be focused on the characterisation and performance evaluation of the nanoporous membranes using the wide range of expertise of the consortium partners. Moreover, in order to demonstrate industrial relevance and high added-value of the membranes developed in SELFMEM, they will be tested under industrially relevant conditions for their potential applications in gas separation, water treatment, and filtration of biological entities. The ultimate goal is to achieve transfer of prototypes or laboratory processes to industrial partners.

Self-assembly is an intrinsic property of matter which occurs on different length scales, ranging from atomic length scales, found in crystals of inorganic salts or low-molecular organic compounds, to larger length scales found in amphiphiles building the structures within living cells (i.e. bilayers, vesicles, liposomes, and tubules). The latter often function as membranes, and therefore are of fundamental importance for life. As an important example from synthetic polymer chemistry, amphiphilic block copolymers should be mentioned, which self-assemble into superstructures such as micelles in solutions, or into crystal-like superstructures in the bulk phase. The driving forces for this self-assembly are non-covalent forces, e.g. van der Waals interactions, ionic forces, hydrogen bonds, and entropic interactions, or their combinations. The formed superstructures often display special functionalities, not present in the individual building blocks. Prominent examples in macromolecules of biological origin are the double-helix of DNA storing the genetic code or the secondary, tertiary and quaternary structures of proteins, in which the spatially directed hydrogen bonds are very important for the self-organisation and their function as enzymes or structural building blocks (e.g. silk, collagen). Thus, it is not surprising that the generation of novel materials with special functionalities via self-assembly of designed molecules has become a cornerstone in nanotechnology.

In this project, our goal is to understand the self-assembly in block copolymer membranes in order to generate isoporous membranes with high pore density for gas separation, the separation of biomolecules and water treatment, based on block copolymer self-assembly using several concepts. Our objective is to develop radically new approaches for the preparation of both organic and inorganic ultrathin membranes (thickness < 100 nm) with high pore density. Preparation methods are based on the use of block copolymer self-assembly to generate nanopores of tunable dimensions (a few nm up to 50 nm) and narrow size distribution. For this purpose, we intend to understand the self-assembly of block copolymers from solution into thin films and on top of different substrates, which are meaningful for the membrane preparation process. We will study the (micro) phase separation and morphology generation processes of different systems by experimental methods, and relate this information to theory and computer simulations. Moreover, we will use the outcome of theoretical calculations and computer simulations to optimise the preparation methods and take maximum advantage of the self-assembly ability in block copolymers for nanoporous membrane applications.

Due to their controlled dimensions on the nanometer scale, these nanoporous membranes are expected to provide much higher separation rate, and enhance selectivity towards the filtration of small molecules, and thus overcome today's technology barriers. To demonstrate the added value of nanoporous membranes developed in SELFMEM, they will be optimised, evaluated and compared to existing technologies of gas filtration, water treatment and purification and separation of biological entities. An important feature of the SELFMEM project is the two distinct approaches to be considered for the preparation of nanoporous membranes. Both methods are based on the use of block copolymers to achieve the formation of nanopores, but fabrication techniques lead in one case to polymeric membranes and in the other case to silicon-based membranes. Both types of membranes can be further modified by post-functionalisation. It is a real strength of the proposal to provide complementary technologies for production of both ductile organic and high temperature and pressure resistant inorganic nanoporous membranes, leading to a wide range of potential applications. The development of these membranes will be based on the understanding of the morphology generation processes, the key part of the research in this project. The different routes are described in more detail below.

Concept 1: Isoporous membranes by phase inversion of block copolymer solutions
Before initiating this project, it has been shown by HZG that isoporous membranes can be obtained by a solution casting process, followed by immersion of the cast film into a precipitant for a diblock copolymer, which involves exchange of solvent by non-solvent in the solution film. This procedure leads to a thin isoporous layer on top of a sponge-like porous support made of the same material. This so-called integral asymmetric membrane is most likely the result of a complex interplay between equilibrium and non-equilibrium processes, i.e. microphase separation between the different blocks (ordered top layer) and macrophase separation from the non-solvent (sponge-like bottom area), leading to a frozen-in demixed structure. From permeation studies, it was concluded that the cylindrical domains of this sample have an effective free pore diameter of circa 8 nm, which should be applicable for filtration of biopolymers such as proteins.

In principle, this opens a way to the fabrication of larger scale membranes by a rather simple procedure. However, the described process involves many parameters, such as the thermodynamic properties of the multicomponent system of block copolymer, solvent(s) and nonsolvent(s), the evaporation time of the solution film before immersion into the non-solvent, and even the structural evolution of the block copolymer in the solvent prior to casting. Thus, variation of these parameters leads to different structures. For example, structures with cylinders, oriented in parallel rather than perpendicular to the surface in the top layer, may be obtained. Therefore, a systematic study of structure formation is required. We propose to systematically vary the chemistry and topology of the block copolymers, taking advantage of different controlled polymerisation techniques, such as anionic polymerisation, group-transfer polymerisation (GTP), atom transfer radical polymerisation (ATRP), nitroxide mediated radical polymerisation (NMP), and reversible addition fragmentation chain-transfer polymerisation (RAFT). Besides the cylindrical morphology, also bicontinuous morphologies, such as the gyroid, are of interest, since in the latter case there is no problem with the orientation of the channels in the top layer. An experimental disadvantage of the gyroid phase relative to the cylindrical phase is its much smaller stability region in the compositional phase diagram of diblock copolymers. Fortunately, it has been shown recently via various theoretical approaches that this disadvantage is peculiar for the simple AB diblock copolymers, while in more complex systems, such as linear ABC triblock terpolymers with a comparatively long non-selective middle block, the gyroid and other bicontinuous morphologies (single gyroid and orthorhombic network phase) are stable in a much larger composition range of the phase diagram. This theoretical prediction indicates the necessity of more intense dialog between experiment and theory.

The structural evolution of these polymers will be studied in solution prior to film casting and during the film formation by a number of complementary techniques such as static and dynamic light scattering, X-ray scattering and cryogenic electron microscopy. Modelling results of the structure formation will be compared with experiment.

Concept 2: Silicon-based free-standing nanoporous membranes

Recently, CSEM has developed a clean-room compatible approach for wafer-scale fabrication of silicon-based free-standing nanoporous membranes with thickness < 100 nm and pore size of about 35 nm. These membranes were produced by a proprietary process combining block copolymer lithography and standard microfabrication techniques. Here, the use of responsive block copolymers allows precise control of the size and size-distribution of the nanopores (typically from a few nm to a few tens of nm), as well as the final thickness of the membrane. The porosity of such membrane is > 20 % (i.e. 1010-1011 pores/cm2), a value superior by two orders of magnitude to commercially available track-etched membranes (108-109 pores/cm2). Moreover, due to their large lateral dimensions (supported structure), these membranes are easy to handle, and are accessible without special equipment for their integration into different macroscopic devices. They also show remarkable mechanical properties, since they withstand a differential pressure of several bars.

Within this project, we will aim to further improve the control of pore size, size distribution and periodic arrangement of the nanopores by adjusting the composition and molecular weight of the block copolymer that are used to define the pore nanostructure. Here, we will highly benefit from the competence of the partners involved in simulation and block copolymer chemistry. We will also optimise fabrication processes to be able to produce a series of membranes (Si, SiN, SiO2) at low cost, covering a large range of pore size, porosity and thickness, to cover the entire spectrum of potential applications in ultrafiltration.

Concept 3: Functionalisation of nanoporous membranes

As indicated before, an additional aim of the project is the introduction of new functionalities to the aforementioned membranes by chemical post-treatment. Indeed, selective functionalisation can be achieved either by covering the top of the membrane, or by decorating the interior of nanopores with functional films or (bio)molecules. For instance, such treatments will include the grafting of stimuli-responsive polymers into the membrane nanopores to provide controlled permeability, depending on external environmental conditions (temperature, pH, salinity), or cleavage of the bonds between different blocks after structure formation, as was demonstrated successfully on thin block copolymers layers before. Especially, the control of the pore size down to a nanometre by pyrolysis of polymeric fillers inside the pores of an inorganic membrane will allow the generation of gas separation membranes with inverse selectivity. Decoration of membrane nanopores with biomolecules such as antibodies, enzymes and DNA, or catalytic coatings will also be considered, because it was shown that nanoconfinement drastically increases the probability of recognition events. The expertise of SELFMEM partners in surface (bio)chemistry is definitively an asset for the successful design of new functional nanoporous membranes.

Using this combined approach, we should gain deeper insight into the factors controlling the formation of functional nanoporous membranes of controlled design, leading to the production of both organic and inorganic isoporous membranes with unsurpassed selectivity.

The objectives of SELFMEM are the following:
- 1. Understanding self-assembly of block copolymers into cylindrical and gyroidal morphologies on top of different substrates, by definition of the involved parameters and study of the thermodynamic and kinetic processes occurring from the polymeric solution to the thin film.
2. In-depth investigation of the formation of integral asymmetric isoporous block copolymer membranes.
3. Investigation of thickness and pore size control in the formation of silicon-based membranes.
4. (Bio)functionalisation of both asymmetric block copolymer and Si-based nanoporous membranes, using several approaches such as selective degradation of a block or cleavage of the junction between blocks, polymer analogous reactions on a block, grafting of responsive polymers, immobilisation of biomolecules, functionalisation with catalytic molecules.
5. Extensive characterisation of the membranes in terms of mechanical properties, porosity, liquid/air flow rate and selectivity.
6. Demonstration of the performances of the nanoporous membranes for key industrial applications: i) gas separation with special focus on CO2, ii) water purification for medical purposes, and iii) biomolecule filtration / fractionation.
7. Optimisation of fabrication methods to offer cost-effective solutions (in relation to the level of performance).

Potential impact:

The research carried out within SELFMEM led to a number of new isoporous membranes based on block copolymers using the phase inversion technique or using block copolymers as templating masks to generate isoporous inorganic membranes.

The block copolymer membranes showed very promising filtration properties and strategies to postfunctionalise the membrane structures were developed, which open the way to different applications starting from a given isoporous block copolymer membrane.

Concerning ultrathin nanoporous silicon membranes NSiMs, the SELFMEM project has allowed the optimisation and up-scaling of the successive micro- and nano-fabrication processes for the wafer scale production of NSiMs. It results therefore a strong consolidation of the membrane manufacturability and process reliability that are both requested for a successful transfer and industrialisation of the membrane technology. In addition, through the integration of NSiMs into functional fluidic and filtration modules, the SELFMEM project has allowed us to demonstrate the membrane performances and to evaluate their applicability for (bio)molecules separation, ultrafiltration or sensing.

Although none of the developed systems led to a breakthrough in the specific applications envisioned by the industrial partners of this consortium, the obtained results are of potential interest for the scientific community. In addition, complementary investigations are currently carried out with the main goal to evaluate the potential of isoporous membranes in other fields of applications such as nanotoxicology, drug delivery, sensing or diagnostics.

Besides a number of publications also four patents were submitted, underlying the technological potential of some of the results obtained in SELFMEM.

Submitted patents:

- 'Membran mit isopöroser trennakiver Schicht und Verfahren zur Herstellung einer Membran (Salz)', Abetz, Filiz, Gallei, Rangou, DE 102012207338.8 03.05.2012
- 'Membran mit isoporöser trennaktiver Schicht und Verfahren zur Herstellung einer Membran (Phaseninversion)', Abetz, Filiz, Hahn, Rangou, DE 102012207344.2 03.05.2012
- 'Thermoresponsive Filtrationsmembran (Membranmodifizierung durch pNIPAM', Abetz, Clodt, Filiz, Rangou, EP 12179780.7 09.08.2012
- 'Herstellung einer Blockcopolymermembran durch Zusatz von Zucker', Abetz, Clodt, Filiz, Buhr, EP 12179792.2 09.08.2012.

A number of oral and poster contributions were given on various international conferences, also a SELFMEM session was held within the World Filtration Congress WFC 11, held in Graz on 16-20 April 2012.

In the following, we just list the written publications in peer-reviewed journals and also PhD thesis which emerged from the SELFMEM project.

Publications in peer-reviewed journals

Janina Hahn, Volkan Filiz, Sofia Rangou, Juliana Clodt, Adina Jung, Kristian Buhr, Clarissa Abetz , Volker Abetz
'Structure Formation of Integral-Asymmetric Membranes of Poly(styrene-block-ethylene oxide)'
Journal of Polymer Science, Part B: Polymer Physics, in print
DOI: 10.1002/polb.23209

Anna Glagoleva, Igor Erukhimovich, Valentina Vasilevskaya
'Voids' microstructuring in lamellar phase of amphiphilic macromolecules'
Macromolecular Theory and Simulations, accepted.
Kyriaki S. Pafiti, Costas S. Patrickios, Volkan Filiz, Sofia Rangou, Clarissa Abetz, Volker Abetz
'Styrene - Vinyl Pyridine Diblock Copolymers: Achieving High Molecular Weights by the Combination of Living Anionic and Reversible Addition-Fragmentation Chain Transfer Polymerizations'
Journal of Polymer Science, Part A: Polymer Chemistry, in print
DOI: 10.1002/pola.26369

Cé Guinto Gamys, Alexandru Vlad, Olivier Bertrand, Jean-François Gohy
'Functionalized Nanoporous Thin Films From Blends of Block Copolymers and Homopolymers Interacting via Hydrogen Bonding'
Macromolecular Chemistry and Physics, accepted
DOI: 10.1002/macp.201200255.

Marios Elladiou, Costas S. Patrickios
'2-(Pyridin-2-yl)ethanol as Protecting Group for Carboxylic Acids: Chemical and Thermal Cleavage, and Conversion of Poly[2-(Pyridin-2-yl)ethyl Methacrylate] to Poly(methacrylic Acid)'
Polymer Chemistry (RSC) 2012, accepted as a Communication
DOI: 10.1039/C2PY20601C

Juliana Isabel Clodt, Volkan Filiz, Sofia Rangou, Kristian Buhr, Clarissa Abetz, Daniel Höche, Janina Hahn, Adina Jung, Volker Abetz
'Double stimuli-responsive isoporous membranes via post-modification of pH-sensitive self-assembled diblock copolymer membranes with pNIPAM-NH2 using polydopamine as a coating'
Advanced Functional Materials 2012, in print
DOI 10.1002/adfm.201202015

Adina Jung, Sofia Rangou, Clarissa Abetz, Volkan Filiz, Volker Abetz
'Structure formation of integral asymmetric composite membranes of polystyrene-block-poly(2-vinylpyridine) on a nonwoven'
Macromolecular Materials and Engineering 2012, 729(8), 790-798
DOI: 10.1002/mame.201100359

Igor Erukhimovich, Yury Kriksin, Gerrit ten Brinke
'The diamond and other non-conventional morphologies in multi-block two-scale AB copolymers'
Soft Matter, accepted
DOI:10.1039/C1SM06688A

Mirela Zamfir, Costas S. Patrickios, Franck Montagne, Clarissa Abetz, Volker Abetz, Liat Ronen, Yeshayahu Talmon
'Styrene - Vinyl Pyridine Diblock Copolymers: Synthesis by RAFT Polymerization and Self-assembly in Solution and in the Bulk'
Joural of Polymer Science, Part A: Polymer Chemistry 2012, 50, 1636-1644
DOI : 10.1002/pola.25935

Cé Guinto Gamys, Jean-Marc Schumers, Alexandru Vlad, Charles-André Fustin, Jean-François Gohy
'Amine-functionalized nanoporous thin films from a poly(ethylene oxide)-block-polystyrene diblock copolymer bearing a photocleavableo-nitrobenzylcarbamate junction'
Soft Matter 2012, 8, 4486-4493

Jean-Marc Schumers, Olivier Bertrand, Charles-André Fustin, Jean-François Gohy
'Synthesis and self-assembly of diblock copolymers bearing 2-nitrobenzyl photocleavable side groups'
Journal of Polymer Science Part A: Polymer Chemistry 2012, 50, 599-608

Jean-Marc Schumers, AlexandruVlad, Isabelle Huynen, Jean-François Gohy, Charles-Andre Fustin
'Functionalized nanoporous thin ?lms from photocleavable block copolymers'
Macromolecular Rapid Communication 2012, 33, 199-205

Haizhou Yu, François Stoffelbach, Christophe Detrembleur, Charles-André Fustin, Jean-François Gohy
'Nanoporous thin films from ionically connected diblock copolymers'
European Polymer Journal 2012, 48, 940-944

Clement Mugemana, Jean-François Gohy, Charles-André Fustin
'Functionalized Nanoporous Thin Films from Metallo-Supramolecular Diblock'
Langmuir 2012, 28, 3018-3023

Franck Montagne, Nicolas Blondiaux, Alexandre Bojko, Raphael Pugin
'Molecular transport through nanoporous silicon nitride membranes produced from self-assembling block copolymers'
Nanoscale 2012, 4, 5880-5886

M. J. K. Klein, F. Montagne, N. Blondiaux, O. Vazquez-Mena, H. Heinzelmann, R. Pugin, J. Brugger, V. Savu
'SiN membranes with submicrometer hole arrays patterned by wafer-scale nanosphere lithography'
Journal of Vacuum Science and Technology B 2011, 29(2), 021012-1 - 021012-5

Manuscripts submitted to peer-reviewed journals being presently under review:

Juliana Isabel Clodt, Volkan Filiz, Sofia Rangou, Anne Schröder, Kristian Buhr, Janina Hahn, Adina Jung, Volker Abetz
'Carbohydrates as additives for the formation of isoporous PS-b-P4VP diblock copolymer membranes'
Macromolecular Rapid Communications

Liat Oss-Ronen, Judith Schmidt, Volker Abetz, Aurel Radulescu, Yachin Cohen, Yeshayahu Talmon
'Characterization of Block Copolymer Self-Assembly: From Solution to Nanoporous Membranes'
Macromolecules

PhD theses:

Jean-Marc Schumers
'Development of photocleavable block copolymers as precursors for functional nanomaterials'
Université catholique de Louvain, 2010

Clément Mugemana
'Use of metal-ligand complexes to control the self-assembly of block copolymers'
Université catholique de Louvain, 2011

PhD thesis which will be finished after the end of SELFMEM:

Adina Jung
'Integral asymmetric membranes made of diblock and triblock copolymers: Synthesis, Membrane Formation and Characterisation'
Universität Hamburg, 2013

Janina Hahn
'Integral asymmetric membranes of diblock copolymers containing 4-vinyl pyridine or ethylene oxide as the hydrophilic block component'
Universität Hamburg, 2014

Marios Elladiou
'Pyridine-containing polymethacrylates: Synthesis and stability'
University of Cyprus, 2016

Corinna Stegelmeier
'Herstellung und Strukturbildungsprozess von mesoporösen Blockcopolymer-Membranen'
Universität Bayreuth, 2013

List of websites: http://www.selfmem.eu and http://www.selfmem-dissemination.org

Contacts of the teams from Academia:

Prof. Dr. Volker Abetz
Helmholtz-Zentrum Geesthacht
Institut für Polymerforschung / Institute of Polymer Research
Max-Planck-Straße 1
D-21502 Geesthacht, Germany

Prof. Dr Yeshayahu (Ishi) Talmon
Prof. Dr Yachin Cohen
Department of Chemical Engineering
Technion-Israel Institute of Technology
IL-Haifa 32000, Israel

Prof. Dr Jean-Francois Gohy
Université catholique de Louvain - IMCN BSMA
Place Louis Pasteur 1 bte L4.01.01
B-1348 Louvain-la-Neuve, Belgium

Prof. Dr Stephan Förster
Universität Bayreuth
Lehrstuhl für Physikalische Chemie I
Universitätsstrasse 50
D-95447 Bayreuth, Germany

Prof. Dr Costas S. Patrickios
University of Cyprus
Department of Chemistry
75 Kallipoleos Avenue
P.O. Box 20537
CY-1678 Nicosia, Cyprus

Dr Raphaël Pugin
Swiss Center for Electronics and Microtechnology (CSEM)
Division of Nanotechnology and Life Science
JaquetDroz 1
CH-2002 Neuchâtel, Switzerland

Prof. Dr Guojun Liu
Department of Chemistry
Queen's University
90 Bader Lane
Chernoff Hall, Room 411
Kingston, Ontario
Canada, K7L 3N6

Prof. Dr Igor Erukhimovich
A. N. Nesmeyanov Institute of Organoelement Compounds
Russian Academy of Sciences
Vavilova str. 28
RU-119991 Moscow, Russia

Contacts of the teams from industry:

Dr Jan-Willem Handgraaf
Culgi B. V.
P.O. Box 252
NL-2300 AG Leiden, the Netherlands

Dr Pluton Pullumbi
Air Liquide, Centre de Recherche Claude Delorme
B.P. 126, Les Loges-en-Josas
F-78354 Jouy-en-Josas, France

Michel Faupel
Rhenovia Pharma
Technopole - Mer Rouge Plaza
20C rue de Chemnitz
F-68200 Mulhouse Cedex, France

Dr Peter Levison
Pall Europe Limited
5 Harbourgate Business Park
Southampton Road
UK-Portsmouth PO6 4BQ, United Kingdom

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