Depth sensing indentation of nanoscale graphene platelets in nanocomposite thin films
- PDF / 250,822 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 85 Downloads / 170 Views
Depth sensing indentation of nanoscale graphene platelets in nanocomposite thin films Ardavan Zandiatashbar, Catalin R. Picu and Nikhil Koratkar Department of Mechanical, Aeronautical and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY, 12180, U.S.A. ABSTRACT Significant improvement of mechanical properties was observed recently in graphene platelet-epoxy nanocomposites relative to unfilled epoxy, such as an increase of the fracture toughness by 50% and dramatic decrease of fatigue crack growth rate. In this work, thin films of 0.1 wt.% of graphene platelet (GPL) – epoxy nanocomposites were fabricated and the nanoscale mechanical properties of the nanocomposite were investigated by nanoindentation. This provides information about the presence of characteristic length scales induced by the microstructure and the strength of the filler-matrix interface. INTRODUCTION Carbon based nanoparticles attracted considerable attention recently as a result of their outstanding properties. Quasi-one dimensional carbon nanotubes and two dimensional graphene were used to enhance the mechanical properties of epoxy-based nanocomposites. In particular, significant toughening was observed in epoxy-based nanocomposites with graphene as nanoscale fillers [1-4]. The fracture toughness increases by approximately 20% and 50% upon the addition of only 0.1 wt% of carbon nanotubes and graphene platelets, respectively [5]. In cyclic loading the crack growth rate decreases by an order of magnitude relative to the unfilled epoxy [5,6]. The nanoindentation technique is widely used today to probe the local material behavior. As long as the film stiffness if smaller than that of the substrate and the indentation depth is kept smaller than a fraction of the film thickness (less than 10%), the measured response is considered to be characteristic for the properties of the film material [7-10]. In this article, results of nanoindentation tests performed on 0.1 wt. % GPL – epoxy nanocomposite and pure epoxy films are presented. The films are deposited on a silicon substrate by spin coating. Atomic force microscopy (AFM) is used to investigate the surface roughness of samples as well as to characterize the fillers located close to the upper surface. EXPERIMENT Samples preparation Nanocomposite films with 0.1% weight fraction of nanofillers were prepared in a sequential manner. The graphene platelets used in this work were prepared by thermal reduction of graphite oxide [3]. Nanofillers were dissolved in 100-200 ml acetone per 0.1 gr of nanofiller and dispersed using an ultrasonic probe sonicator (Sonics Vibracell VC 750, Sonics and Materials Inc., USA) for 45 minutes, followed by adding epoxy resin (System 2000 Epoxy Resin, Fibreglast Inc., USA) to this suspension while continuing sonication. The solution was heated at 70°C and stirred using a Teflon-coated magnetic bar on a magnetic stir plate for 3
379
hours in order to evaporate the solvent. The procedure was followed by keeping the mixture in vacuum (-30mmHg) at 70°C
Data Loading...
