Layer-by-layer preparation of polyelectrolyte multilayer membranes for separation Nithya Joseph, a Pejman Ahmadiannamini, a Richard Hoogenboom * b and Ivo. F. J. Vankelecom * a Polymer membranes provide a highly promising platform for the development of an efficient and sustainable technique for separation. Ideally such membranes combine a high flux with a high selectivity requiring thin defect-free membranes. The layer by layer (LBL) assembly technique has proven to be a versatile and simple method for the fabrication of very thin polyelectrolyte multilayers making it highly suitable for the preparation of separation membranes. Recent developments in this field related to membrane preparation and their applications in separation processes are presented and discussed in this review. An overview of the different fabrication techniques of such membranes will be first provided. In addition, the formation mechanism and the parameters that can be varied to tune the properties of the membranes will be discussed. Finally, the potential applications of these membranes in different separation areas such as pervaporation, nanofiltration, solvent resistant nanofiltration, reverse osmosis, gas separation and forward osmosis will be addressed. 1. Introduction Membrane based separations have become more and more important in recent years since they can operate with very low energy consumption, high efficiency and are robust enough for long-term application. As such, membrane separations repre- sent sustainable and oen more cost-efficient alternatives to classical separation methods such as distillations, crystalliza- tions, extractions, preparative chromatography, etc. Ideal sepa- ration membranes should possess both high ux and high selectivity, while being stable during long-term operation. Nithya Joseph was born in Ker- ala, India. She did her Master’s in Polymer Engineering from Birla Institute of Technology, Mesra (India, 2007). She is now doing her PhD at Center for Surface Chemistry and Catal- ysis, KU Leuven (Belgium), under the supervision of Prof. Ivo Vankelecom. Her research focuses on synthesis and appli- cations of polyelectrolyte multi- layer membranes. Pejman Ahmadiannamini obtained his BSc (Chemical Engineering) at University of Isfahan (Iran, 2004). He received his MSc (Chemical Engineering) from Sahand University of Technology (Iran, 2007). In 2008, he moved to KU Leuven (Belgium) and started his PhD at the Center for Surface Chemistry and Catalysis. He is currently a research associate post-doctoral fellow at Dept. of Civil and Environmental Engineering, Michigan State University. His areas of expertise comprise membrane preparation and char- acterization, solvent resistant nanoltration and environmental application of nanotechnology. a Centre for Surface Chemistry and Catalysis, Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Kasteelpark, Arenberg-23, P.O Box 2461, 3001 Leuven, Belgium. E-mail: ivo.vankelecom@biw.kuleuven.be; Web: http://www.biw. kuleuven.be/m2s/cok/Groups/membrane-technology; Fax: +32 16321998; Tel: +32 16321594 b Supramolecular Chemistry Group, Department of Organic Chemistry, Faculty of Sciences, Ghent University, Krijgslaan 281 S4, B-9000, Ghent, Belgium. E-mail: Richard.Hoogenboom@ugent.be; Web: http://www.sc.ugent.be; Fax: +32 92644998; Tel: +32 92644482 Cite this: Polym. Chem. , 2014, 5, 1817 Received 10th September 2013 Accepted 16th September 2013 DOI: 10.1039/c3py01262j www.rsc.org/polymers This journal is © The Royal Society of Chemistry 2014 Polym. Chem. , 2014, 5, 1817–1831 | 1817 Polymer Chemistry REVIEW