Nanocomposites of polypropylene were prepared with different loadings of both commercially-available graphene and graphene that had been modified with low molecular weight polypropylene brushes. The dependence of the thermal stability, electrical conductivity and mechanical properties of the composites on the type and loading of the graphene filler have been investigated. The mechanical properties were studied using several techniques, including nanoindentation, four-point bending coupled to Raman spectroscopy and tensile testing. Significant differences on the mechanical performance, due to the influence of graphene content and modification, have been observed; i.e. t ¡ ¢ £ ¤ ¥ ¦ § ¨ © values up to 30% higher for nanocomposites with modified graphene, compared to those with pristine graphene. Different trends on the variation of mechanical properties have been encountered at the local and macro scales and a discussion of the respective results from the different techniques is offered. Finally, the behavioral changes on the electrical conductivity are also discussed.

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...

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Nanoindentation provides clear evidence that spherulite banding can be associated with a continuous modulation of mechanical properties from the more compliant peaks to the stiffer valleys. The structural arrangement in polymer-banded spherulites has intrigued scientists for many decades, and the debate has been recently intensified with the advent of new experimental evidence. The present paper approaches this issue by exploring the local mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-ringed spherulites via nanoindentation and discussing the confidence of the results. It was found that storage modulus and hardness across the banding morphology can be described as a sequence of regular oscillations with a periodicity that exactly matches the one observed using optical and atomic force microscopy. Results are consistent with the model of regular twisting of the lamellae, with flat-on arrangement in the low regions and edge-on lamellae in the crests.

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PEEK appears as an excellent candidate to substitute epoxy resins in carbon fibre laminates for high-performance aeronautical applications. The optimization of the properties and, in particular, of the transition region between the fibres and the matrix appear as a major issue prior to serial production. Graphene, modified with two compatibilizers, has been incorporated in the polymer layer with the purpose of imparting additional functionalities and enhancing the matrix-fibre interaction. It is found that both carbon fibres and modified graphene significantly influence the crystallization behaviour and smaller, and/or more imperfect crystals appear while the degree of crystallinity decreases. Despite this, nanoindentation studies show that the PEEK layer exhibits significant modulus improvements (≈30%) for 5 wt.% of graphene. Most importantly, the study of the local mechanical properties by nanoindentation mapping allows the identification of remarkably high modulus values close to the carbon fibre front. Such a relevant mechanical enhancement can be associated with the accumulation of graphene platelets at the polymer–fibre boundary, as revealed by electron microscopy studies. The results offer a feasible route for interlaminar mechanical improvement based on the higher density of graphene platelets at the fibre front that should promote interfacial interactions. Concerning electrical conductivity, a large anisotropy was found for all laminates, and values in the range ~10−4 S/cm were found for the through-thickness arrangement as a consequence of the good consolidation of the laminates.