Graphene-MWNTs composite coatings with enhanced electrical conductivity

The large-scale production of graphene with minimal defects and high electrical conductivity is one of the challenges of the field. Despite several methods available for graphene synthesis, new methods need to be investigated which are economically viable, are simple to implement and above all are environmentally friendly – key factors for enabling graphene production. This article demonstrates the production of high quality graphene through liquid exfoliation (a top-down method) under high shear forces using surfactant and water as the dispersive medium, making it a highly eco-friendly process. The exfoliated graphene flakes were functionalized using the amino siloxane derivative 3-(Aminopropyl)triethoxysilane (APTES) into which exfoliated and functionalized multi-walled carbon nanotubes (MWNTs; functionalized using an amino silane derivative) were added in order to prepare graphene-MWNT composites along with the binder i.e. Dynasylan® SIVO 110. The role of the MWNTs is to enhance the electrical conductivity of the resulting graphene films by bridging the adjacent graphene sheets that are oriented in a random fashion. Significantly, it is observed that the functionalization groups added to both the graphene and MWNTs serves multiple roles: (i) enhancing the adhesion strength of the prepared composite mixture to glass substrate and (ii) functionalizing the edges of the graphene to create a 3D cross-linked structure of graphene and MWNT. The composite films were prepared using the doctor blade method followed by sintering at two different temperatures, namely 120 °C and 400 °C, resulting in sheet resistance values of 3 ± 0.1 kΩ/sq and 34 ± 5 Ω/sq, respectively.