In this study, poly(methyl methacrylate) (PMMA)/graphene nanoplatelets (GNPs) conductive composite films with different morphologies were fabricated from the same constituent materials using four fabrication techniques, solution casting (SC), SC followed by hot pressing (SCP), melt mixing followed by SC (MSC), and melt mixing followed by hot pressing (MP). Morphologies of dispersed GNPs and electrical properties in both in-plane and perpendicular directions were investigated and compared systematically. The conductivities, which varied up to two orders of magnitude and decreased in the sequence of SC > MSC >SCP >MP, were described as a function of GNPs volume fraction by using a McLachlan equation to reveal the electrical percolation thresholds (Φc). The Φc of the composites varied from 0.42 ± 0.13 vol % (SC, perpendicular) to 3.26 ± 0.48 vol % (MP, in-plane). The difference in the conductivity and Φc between two measuring directions is ascribed to GNPs orientation, while that for different processing methods is explained in terms of GNPs size, GNPs distribution, and dispersion state. The contribution of the above factors in each procedure was discerned individually, the results were discussed and compared with other experimental studies and simulations as well. The comparative study shows that the SC method endows the composite with the optimum electrical properties in both directions due to the large size, good dispersion and exfoliation of GNPs, and bad distribution of segregation structures.
Xiaoling Luo is a Ph. D student at the Institute of Polymer Materials, Friedrich-Alexander-University Erlangen-Nuremberg, Germany. She received a B.S. (2014, Polymer Science and Engineering) and M.S. (2017, Polymer Science and Engineering) from Sichuan University, China. Her research is focused on the fabrication, characterization, modeling and application of conductive polymer composites containing carbon-based fillers under the supervision of Prof. Dirk W. Schubert.
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