Experimental and theoretical study of the evolution of fluid-suspended graphene morphology driven by an applied electric field and the attainment of ultra-low percolation threshold in graphene-polymer nanocomposites
By Du, Han; Spratford, Shane; Shan, Jerry W.; Weng, George J.
Published in Composites Science and Technology
2020
Abstract
We report on a coordinated experimental and theoretical investigation into the evolution of the morphology of fluid-suspended graphene driven by an electric field, and the attainment of ultra-low percolation threshold in graphene-polymer nanocomposites. A remarkable outcome is that, due to the field-driven graphene rotation and agglomerate chaining, the percolation threshold can be as low as 0.03 vol%, as opposed to the 0.75 vol% without the application of the field. This is likely to be the lowest ever reported for a graphene-polymer nanocomposite. To quantify this and other measured conductivity data, a two-scale effective-medium theory with highly aligned, agglomerated nanofillers is developed. In this process Cauchy's cumulative probability function is introduced to describe the increased level of electron tunneling near the percolation threshold, and a statistical approach based on the projection length of graphene fillers is developed to characterize the agglomerate shape. We also built a kinetic equation from the torque of the applied electric field to calculate the time- and field-dependent rotation of graphene nanoplatelet. The study is highlighted with a direct comparison between the theory and the experiment. It is concluded that the measured ultralow percolation threshold can indeed be achieved through the concurrent graphene rotation and elongation of agglomerate shape toward the field direction.