Development of Advanced Elastomeric Conductive Nanocomposites by Selective Chemical Affinity of Modified Graphene

Abstract

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...

Structural Behavior of Cylindrical Polystyrene‐block‐Poly(ethylene‐butylene)‐block‐Polystyrene (SEBS) Triblock Copolymer Containing MWCNTs: On the Influence of Nanoparticle Surface Modification

“…The complex microstructure of BCP materials does not only render them interesting for purely academic purposes, but also because of their wide range of applications such as photolithography, medicine, electronics, and gas separation . In order to further improve their properties, various studies have investigated the incorporation of nanoparticles into block copolymers as a highly promising method to tailor the material's properties and enhance their mechanical, electrical, and thermal properties …”

“…[5][6][7][8] In order to further improve their properties, various studies have investigated the incorporation of nanopar ticles into block copolymers as a highly promising method to tailor the material's properties and enhance their mechanical, electrical, and thermal properties. [9][10][11][12][13][14][15][16][17] Carbon nanotubes (CNTs) are very promising nanomaterials due to the com bination of their superlative thermal, mechanical, and electrical properties. [18][19][20][21] CNTs tend to agglomerate and form strongly entangled bundles, driven by van der Waals forces.…”

New Perspectives on Graphene/Polymer Fibers and Fabrics for Smart Textiles: The Relevance of the Polymer/Graphene Interphase

“…In the last few years, we have focused our investigation on the design of specific synthetic protocols for graphene functionalization, where the chosen chemical modification is designed around the target polymer where graphene is to be incorporated. These approaches have progressed from functionalization with discrete molecules (Salavagione et al, 2009b;Coşkun et al, 2012;Castelaín et al, 2013c), to the covalent bonding of graphene to polymers (Salavagione et al, 2009a;Salavagione and Martínez, 2011;Castelaín et al, 2012) and the functionalization of graphene with short polymer brushes (Castelaín et al, 2013a,b;Salavagione, 2014;Quiles-Diaz et al, 2016;Salavagione et al, 2016;Enrique-Jimenez et al, 2017;Quiles-Díaz et al, 2017). The former method uses simple chemical reactions and can lead to good functionalization levels.…”

Polystyrene Chain Growth from Di-End-Functional Polyolefins for Polystyrene-Polyolefin-Polystyrene Block Copolymers

“…Following the commercialization of OBCs by the Dow Chemical Company [6][7][8], Coates et al recently reported the preparation of PE/iPP (iPP = isotactic polypropylene) multiblock copolymers to enhance capabilities of plastic recycling [1]. In addition, connection of PO chains with other polymers such as polystyrene (PS) or polar monomer-based polymers to prepare diverse PO-based block copolymers has also been reported [9][10][11][12][13][14][15][16][17], with a typical example being PO-PS block copolymers, e.g., PS-block-poly(ethylene-co-1-butene)-block-PS (SEBS), which are commercially thermoplastic elastomer properties, SEBS is commonly employed in commodities such as rubbers and plastics [18][19][20][21][22], and its use in new specialized areas is also receiving growing interest [23][24][25][26][27][28][29]. In industry, SEBS is not produced directly from olefin and styrene monomers, but instead by a two-step process that involves the costly hydrogenation of the PS-block-polybutadiene-block-PS (SBS) copolymer produced by the living anionic polymerization of styrene and butadiene [30,31].…”

“…Thus, we herein report an alternative method for the construction of PS-block-PO-block-PS copolymers (Scheme 2), which is expected to provide a number of advantages over previously reported methods. thermoplastic elastomer properties, SEBS is commonly employed in commodities such as rubbers and plastics [18][19][20][21][22], and its use in new specialized areas is also receiving growing interest [23][24][25][26][27][28][29]. In industry, SEBS is not produced directly from olefin and styrene monomers, but instead by a two-step process that involves the costly hydrogenation of the PS-block-polybutadiene-block-PS (SBS) copolymer produced by the living anionic polymerization of styrene and butadiene [30,31].…”