A supramolecular approach toward organo-dispersible graphene and its straightforward polymer nanocomposites† Sunil P. Lonkar, * a Alexis Bobenrieth, a Julien De Winter, ab Pascal Gerbaux, b Jean-Marie Raquez * a and Philippe Dubois a Received 29th June 2012, Accepted 24th July 2012 DOI: 10.1039/c2jm34234k Highly dispersible graphene nanosheets were straightforwardly synthesized by in situ reduction in the presence of hydroxyl-func- tionalized imidazolium ionic liquids as a supramolecular template. Therefrom, a biodegradable poly(3-caprolactone) (PCL)/graphene nanocomposite was prepared via a ‘‘grafting-from’’ approach based on the hydroxyl functionalities available from as-modified graphene nanosheets. The work opens up a path for a wide range of strategies in the fabrication of graphene/polymer nanocomposites. The unique structure of graphene, including its single-atom thickness, two-dimensionality and extensive conjugation, endows it with exceptional properties which hold great promise for potential appli- cations, ranging from various electronic devices to novel nano- composite materials. 1 One of the most promising applications of this material is in the realm of polymer nanocomposites, which are polymer matrix composites that incorporate nanoscale filler mate- rials. 2 When dispersed uniformly, graphene nanosheets may amend the structure–property features of polymers to a great extent. 3 The prerequisite for realizing the excellent performance of graphene layers in polymer nanocomposites is to disperse graphene at the nanoscale. Nonetheless, poor dispersability and strong aggregation of graphene layers into an organic medium challenge their processability in the fabrication of graphene-based organic and polymer composite materials. Therefore, the stabilization and modification of graphene have attracted extensive research interest. 4 An effective approach in this regard is based on the in situ reduction of graphene oxide into graphene sheets in organic media, since most monomers and poly- mers are merely soluble in organic solvents. But the critical bottleneck for the widespread use of single-layer graphene is the absence of a facile method for chemical modifications, which does not diminish the outstanding properties of the two-dimensional sp 2 network. In this regard, several recent reports have commented on the function- alization of graphenes by both covalent and non-covalent approaches. 5 Interestingly, the non-covalent pathway, i.e. the supra- molecular approach, brings out a simple and cost-effective process supplemented by the entire preservation of the electronic structure of such p-conjugated systems. Recently, ionic liquids have seemed well positioned to address this challenge. 6 Due to their wide solubility, functionality, and high surface charge density, modification with such organic ionic species is expected to enable the preparation of long- term stable graphene sheets that can be readily dispersed in various polymeric matrices without any structural defects. In this work, we report a method to produce organo-dispersible- stabilized graphene sheets via non-covalent functionalization of graphene by a functional amphiphilic ionic liquid, namely, 1-(11- hydroxy-undecyl)-3-methyl-imidazolium-N-N-bis(trifluoromethane) sulphonamide (ImOH/TFSI). It is expected that the imidazolium moieties can interact with graphene oxide (GO) through elec- trostatic interactions in aqueous GO-based suspensions, and that post-reduction will occur through p-cation stacking between imidazolium and graphitic structure. Moreover, the hydroxyl functionalities present at the surface of graphene via the presence of Im–OH/TFSI were employed to initiate in situ ring-opening polymerization (ROP) of 3-caprolactone (CL), illustrating the ‘‘grafting-from’’ method as an efficient way to achieve finely dispersed graphene nanosheets within the resulting poly(3-cap- rolactone) (PCL) matrix (Scheme S1†). In addition to its biodegradability and mechanical properties, PCL provides eclectic miscibility characteristics in a variety of polymers that would make the resulting materials exciting in terms of master- batches to produce finely dispersed graphene/polymer nanocomposites. The resulting nanohybrids, Im–OH/TFSI/RGO, present remark- able miscibility (ca. 1 mg mL 1 ) in different organic solvents, forming long-term stable and homogeneous dispersions after a mild ultrasonic treatment. Individual nanolayers can be readily observed after spraying them on a TEM grid as well (Fig. 1). This is mainly due to the strong p–p stacking between the backbones of Im–OH/TFSI and the graphene basal planes, and cation–pi electrostatic interactions between the resulting Im–OH/TFSI/RGO sheets. 7 Such compatibility with several organic solvents would make graphene sheets an ideal candidate for various applications. a Laboratory of Polymeric and Composite Materials (LPCM), Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons, Place du Parc 23, B-7000 Mons, Belgium. E-mail: Sunil.Lonkar@umons.ac.be; jean-marie.raquez@umons.ac.be b Organic Chemistry Laboratory, Mass Spectrometry Center, University of Mons, Place du Parc 23, B-7000 Mons, Belgium † Electronic supplementary information (ESI) available: Experimental details, scheme, Raman and TGA analysis of GO, RGO and Im–OH/TFSI/RGO, images of graphene dispersion in CL. See DOI: 10.1039/c2jm34234k 18124 | J. Mater. Chem., 2012, 22, 18124–18126 This journal is ª The Royal Society of Chemistry 2012 Dynamic Article Links C < Journal of Materials Chemistry Cite this: J. Mater. Chem., 2012, 22, 18124 www.rsc.org/materials COMMUNICATION