Wednesday  |  Frick  |  10:50 AM–11:10 AM

#13843, In Situ Measurement of AC Conductivity to Quantify Unidirectional Alignment of Graphene Nanoplatelets (GNPs) In Epoxy

Graphene nanoplatelets (GNPs) are widely used as conductive fillers for various polymer nanocomposites. However, the actual performance of these materials is much lower than theoretical predictions due to the natural tendency of GNPs to agglomerate. Contemporary techniques for random dispersion do not offer modulation of the orientation of graphene and thereby limit its capabilities, promoting the usage of higher concentrations that can lead to undesirable effects. Electric field alignment is a promising way to obtain significantly improved directional properties with low concentrations of GNPs. This paper presents the use of real time AC conductivity measurements to characterize the unidirectional alignment process of GNPs in a thermoset epoxy polymer. Theoretical modeling of the effects of alternating electric field on a single transversely isotropic GNP reveals the key parameters that influence the alignment process, namely, the size of the platelet, viscosity of the epoxy and the content of GNPs. Considering these parameters, an experimental setup is devised to create an alternating electric field in an aluminum mold separated by epoxy/GNP mixture. Time required for alignment is calculated based on the chain-formation and rotation time obtained from above parameters. Preliminary research shows a two to three-fold increase in electrical conductivity in aligned direction compared to randomly dispersed epoxy/GNP samples. The effects of alignment also reveal an increase in the mechanical strength, resulting in a (10-15%) increase in Young’s modulus in the aligned direction. These significant property improvements also decrease the percolation threshold of randomly dispersed epoxy/GNP sample from 1 wt% to 0.5 wt%. Dielectric spectroscopy of randomly oriented and aligned samples shows a 100% increase in dielectric constant at a frequency of 1000 Hz in the aligned direction.

Sai Tharun Kotikalapudi   Oklahoma State University
Raman Singh   Oklahoma State University