Fabrication and characterization of nickel oxide functionalized graphene oxide-polyacrylamide nanocomposites

Graphene oxide (GO) and its functionalized - modified - reduced derivatives take important place in a variety of technological applications because of their unique electrical conductivity properties and excellent mechanical properties which intrinsically come from two dimensional, sp2 bonded carbon honeycomb crystal structure of graphene and its high specific surface area (~2600 m2 g-1). Having this large surface area allow graphene to be homogenously dispersed in polymer matrix, thus it can be used to fabricate advanced nanocomposites which can be integrated in energy storage systems, physical and biological sensors, flexible electronics and many other applications. Generally, graphene oxide is produced using main three methods known as Hummer method, Brodie method or Staudenmaier method. All these three methods contain a familiar, incredibly cost-effective route; an oxidation reaction of graphite and then followed by exfoliation step to form graphene oxide. Widely accepted, oxygen functional groups on surface graphite oxide allow it to be exfoliated to form graphene oxide. However, oxygen based groups distort intrinsic graphene properties, thus reduction step is needed to yield much accurate graphene form. Several reduction routes have been studied and reported, including chemical treatment, thermal treatment, electrochemical treatment. Some of oxygen groups can be removed, but a portion will remain that can be eliminated by several reduction steps. Besides, the certain functional groups can be chemically anchored on graphene oxide surface in reduction steps. This process is described as functionalization of graphene oxide with like inorganic molecules(e.g., metal oxides) or organic molecules (e.g., polymers). Polymers have been used in many application and product because of being relatively cheaper and easily processed. However, their low mechanical and electrical properties limit their applications in some areas. Most of publication in literature has reported remarkable improvements in mechanical and electrical properties, compared to the bare polymers with a small portion of graphene filler, as crosslinker. But, an important point, the improvements intensely depend on distribution of graphene in polymer matrix and forming interfacial bondings between the graphene and host matrices. Hydrophilic polymer lead the graphene sheets to aggregate owing to interactions between the hydrophilic polymer chains and graphene layers. In contrast, graphene oxide, having oxygen based functional groups anchored on the surface, is more suitable with hydrophilic - organic polymers. However, oxygen based groups hinder intrinsic electrical properties of graphene. Hereby, grafting or intercalating of reduced - functionalized graphene oxide into polymer matrix is the most compatible option among all routes to improve its mechanical and electrical properties, simultaneously. This work has focused on fabrication of nickel oxide functionalized graphene oxide - polyacrylamide nanocomposites, (NiO/GO)n/PAAM, and investigation of their structural, mechanical, electrical properties and self-healing ability. The aim of this study is to observe the effect of nickel oxide functionalized graphene oxide (NiO/GO) amount on structural, mechanical, electrical properties and self-healing ability of nanocomposite samples and compare them with that of (BIS) crosslinked (PAAM) samples to determine the difference between (NiO/GO) and (BIS). In the first step, (NiO/GO)n/PAAM and (BIS)n/PAAM samples were fabricated by using in-situ polymerization of polyacrylamide in presence of (NiO/GO) and (BIS), seperately. Secondly, structural characterization of (NiO/GO)n/PAAM nanocomposite samples were investigated by FTIR analysis and XRD to confirm the nanocomposition and crystal structure occured. After structural correction, mechanical properties, electrical properties and self-healing abilities of (NiO/GO)n/PAAM nanocomposite samples were determined and discussed.