Nanopore size tuning of polymeric membranes using the RAFT-mediated radical polymerization Murat Barsbay a , Olgun Güven a,n , Haad Bessbousse b , Travis L. Wade b , François Beuneu b , Marie-Claude Clochard b,nn a Department of Chemistry, Hacettepe University, 06800 Beytepe, Ankara, Turkey b Laboratoire des Solides Irradiés, CEA-CNRS-Ecole Polytechnique UMR7642, 91128 Palaiseau, France article info Article history: Received 3 December 2012 Received in revised form 28 March 2013 Accepted 11 May 2013 Available online 11 June 2013 Keywords: Synthetic nanopores Membrane Functionalisation Controlled radical polymerization Swift heavy ions Anodic stripping voltammetry abstract Poly(acrylic acid) (PAA) was grafted into the nanochannel walls of track-etched β-PVDF membranes in a controlled manner by RAFT polymerization. PAA-g-PVDF copolymers with various degrees of grafting from 5% to 63% were characterized by ATR-FTIR, X-ray photoelectron spectroscopy and atomic force microscopy (AFM). The controlled fashion of RAFT mediated grafting was demonstrated by size exclusion chromatography (SEC) and AFM. It was observed that the pore diameter decreases steadily with the degree of grafting (DOG) and pores start to be filled by the grafted PAA beyond 40 wt% DOG, based on AFM measurements and 15 wt% DOG, based on electrochemical analysis. The synthesized nanoporous membranes were later transformed into highly sensitive functionalized membrane electrodes (FMEs) by deposition of a thin gold ( 50 nm) layer onto the membrane surfaces without blocking the nanochan- nels. The synthesized FMEs have been found to be sensitive to sub-ppb concentrations of Pb 2+ in square- wave anodic stripping voltammetry (SW-ASV) measurements. The sensitivities of RAFT mediated FMEs compared to those synthesized by conventional free-radical polymerization were found to be almost three times higher at sub-ppb concentrations of Pb 2+ in SW-ASV analysis. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Membrane technology has had a high impact in the chemical and biotechnology industries in the last 30 years. Its main features and advantages came from the low energy consumption and develop- ment of sustainable process. Today the most important industrial market segments are ‘medical devices’ and ‘water treatment’ [1]. In addition novel applications are emerging such as affinity adsorptive membranes, catalytic or sensor systems in addition to classical solute separation by molecular weight discrimination [2]. Track-etched membranes are a special kind of membrane where pores are built ‘one by one’ by swift-heavy ion bombard- ment of polymeric films. Latent tracks made by particle bombard- ment are subsequently etched with specific chemical reagents according to the chemical structure of the trunk polymer. Fabri- cating micro-/nano-structures on solid-state substrates by using heavy ion irradiation and track-etching technique opens a reliable and cost-effective route to micro- and nano-technology. Synthetic nanopores are widely used in many fields, such as ionic transport rectification in nanofluidic diodes [3], DNA detection [4], molecu- lar separation [5], responsive gating [6], and energy conversion [7]. Poly(vinylidene fluoride) (PVDF) has found wide-spread indus- trial applications since the 1960s, because of its excellent mechan- ical and physicochemical properties [8]. PVDF films with etched latent tracks induced by swift heavy ions promise new applica- tions especially for separation and filtration purposes. However, PVDF is highly hydrophobic and a chemical treatment of the pore surfaces is required for the filtration of aqueous solution. The radicals produced by the heavy ion irradiation in the damaged tracks are very stable in β-PVDF due to the crystallinity of the polymer [9]. When the damaged tracks are chemically etched to reveal nanopore channels, the channel diameters change propor- tionally with the etching time and there are still active radicals within the pores. These remaining radicals initiate polymerization under thermal activation with different vinyl monomers to impart chemical functionalization to the nanopore interior without block- ing the pores [8–11]. However, when dealing with acrylate mono- mers, the grafted polymer chains grew anarchically due to many transfer reactions. This conventional method suffers from one simple flaw: the molecular weight and the polydispersity of the grafted chains cannot be controlled. To solve this problem and to tune accurately the nanopores size, many methods can be carried out [12–16]. Controlled radical Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science 0376-7388/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.memsci.2013.05.029 n Corresponding author. Tel.: +90 312 297 7977; fax: +90 312 297 7973. nn Corresponding author. Tel.: +33 1 69 33 45 26; +33 1 69 33 45 54. E-mail addresses: mbarsbay@hacettepe.edu.tr (M. Barsbay), guven@hacettepe.edu.tr (O. Güven), haad.bessbousse@polytechnique.edu (H. Bessbousse), travis.wade@polytechnique.edu (T.L. Wade), francois.beuneu@polytechnique.edu (F. Beuneu), marie-claude.clochard@polytechnique.edu (M.-C. Clochard). Journal of Membrane Science 445 (2013) 135–145