The preparation of conductive nanocomposites of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymers with chemically modified graphene is reported. Graphene has been functionalized with short polyethylene brushes by thiol−ene click chemistry in order to enhance the interactions of the filler with the ethylenic phase of the block copolymer. The presence of graphene modifies the morphology of the SEBS domains, reducing their size and promoting an isotropic distribution of cylinders arranged in hexagonal packing, as shown by SAXS, AFM, and TEM. The elastomeric character of SEBS persists in the nanocomposites with filler content below 1 vol %, retaining high elongation at break. In addition, the percolation threshold for electrical conductivity is found to be slightly above 0.7 vol %, reaching conductivity values of ∼10 −3 S cm −1 for ∼2.5 vol % of filler. These materials represent a new class of flexible conductors that open promising opportunities for applications like actuators or bodily motion sensors.
■ INTRODUCTIONAmong the wide pool of applications of graphene-based materials, polymeric nanocomposites constitute one of the areas of major growth and short-term impact on real applications. 1−5 The nature of the polymeric matrices that can be reinforced with graphene and the strategies used to incorporate this filler are numerous and diverse. 1−5 The key to obtain superior materials lies in the efficient functionalization of graphene to achieve good dispersion and strong interphases between the components, the covalent graphene−polymer coupling being one of the most successful routes. 4,6−8 Alternatively, the functionalization of graphene with short polymer brushes to improve its dispersion on similar polymeric matrices represents another useful strategy. 9−12 Although to a lesser extent, this approach has also been employed with copolymers very different in nature. 13−22 The combination of elastomeric matrices with graphene is very exciting since electromechanical materials find niche applications in crucial fields like flexible electronics, 23 actuators, 24,25 body motion sensing, 26,27 and monitoring structural deterioration in materials. 28 Thermoplastic elastomers like poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymers constitute a special family since they display the physical properties of rubbers but can also be processed as thermoplastics. In spite of their potential, investigation on the incorporation of graphene into a SEBS matrix is limited to a handful of examples, and advances to date are rather modest. 21,29−31 In particular, to the best of our knowledge, conductivity values in the range required for practical applications have not been achieved. The styrenic phase has been commonly used as the target to incorporate graphene in SEBS, aiming at the establishment of π−π graphene/styrene interactions. 21,28,31 However, this route has only yielded improvements in mechanical properties. 21,29,32 These studies have shown that the conductive material (graphene...