Surface Modifications of Graphene-based Polymer Nanocomposites by Different Synthesis Techniques
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Surface Modifications of Graphene-based Polymer Nanocomposites by Different Synthesis Techniques Burcu Saner Okan1, Selmiye Alkan Gürsel2 and Yuda Yürüm2 1 Nanotechnology Research and Application Center, Sabanci University, Orhanli, Tuzla, Istanbul 34956, Turkey 2 Faculty of Engineering and Natural Sciences, Materials Science and Engineering, Sabanci University, Orhanli, Tuzla, Istanbul 34956, Turkey ABSTRACT With the appropriate surface treatments, graphene sheets can be separated from graphite material and the layer-to-layer distance can be extended. In the present work, graphene nanosheets (GNS) were separated from graphite by an improved, safer and mild method including the steps of oxidation, thermal expansion, ultrasonic treatment and chemical reduction. For the production of advanced polymer nanocomposites, the distinguished properties of GNS were combined with the structural properties of conducting polypyrrole by the proposed simple and low-cost fabrication technique. The changes in surface morphologies and surface functional groups were estimated by controlling the polymer coating on graphite oxide (GO) sheets, expanded GO and GNS. INTRODUCTION Graphene, the world’s thinnest sheet – only a single atom thick – has a great potential to provide a new way in energy, computing and medical research [1]. The first graphene sheets were obtained by extracting monolayer sheets from the three-dimensional graphite using a technique called micromechanical cleavage in 2004 [2]. One of the applicable methods is the graphite oxidation in order to reduce the strong bonding between sheets in graphite and to receive monolayer graphene sheet. Potassium chlorate, potassium permanganate, nitric acid, and sulfuric acid are mostly used as oxidizing agents in order to destruct the graphite structure in exfoliation process [3-5]. There have been numerous attempts in the literature to produce graphene sheets by exfoliation or expansion of graphite starting with GO or graphite intercalation compounds. Single graphene sheets are exfoliated from graphite with the thermal expansion and chemical reduction processes [6]. After heat treatment of GO sheets, the crystal lattice planes of graphite flakes are extended and this leads to the formation of expanded graphite called “worm-like” or accordion structure [7]. Graphene sheets have been used as fillers in polymer matrix to improve the characteristic properties of nanocomposites. Researchers have found new methods to enhance the dispersion of graphite nanosheets in a polymer matrix. Chen et. al. demonstrated that sonication process is more applicable to disperse graphite sheets in polymer matrix [8]. This method provides much higher conductive composites than the other composites obtained by conventional methods. In this work, graphene sheets were separated from graphite flakes with an improved, safer and mild exfoliation technique. GO sheets, expanded GO and GNS, the products obtained after each step in the exfoliation process, were used as filler in conducting polypyrrole matrix in order
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