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Directed-assembly of carbon structures in a nonpolar dielectric liquid under the influence of DC-generated electric fields

Oliveira, Luciana, Saini, Deepika, Gaillard, Jay B., Podila, Ramakrishna, Rao, Apparao M., Serkiz, Steven M.
Carbon 2015 v.93 pp. 32-38
carbon nanotubes, electric field, electrical conductivity, graphene, light scattering, mathematical theory, models, particle size, perfluorocarbons, solvents
Externally applied direct current (DC) electric fields have been examined as a means of controllable organization of carbon structures (one-dimensional multi-walled carbon nanotubes of three sizes, quasi two-dimensional exfoliated graphene platelets, and three-dimensional bulk graphite) suspended in a high dielectric strength (i.e., highly resistive) solvent (perfluorocarbon FC-40). The net particle charge of the carbon structures in FC-40 was negligible. This eliminates non-dielectrophoretic (DEP) kinetic motions and allows for examination of isolated DEP forces on the assembly process. At a sufficiently high DC field strength and carbon structure concentration, DEP directed assembly and subsequent formation of electrically conductive networks were observed. The influences of particle size, aspect ratio, concentration, and structure on the assembly and electrical conduction in this system were investigated. Threshold voltage, an operationally defined measure of the applied voltage where current flow first occurred, was used as a characteristic measure of the assembly process. Consistent with charge percolation theory, the threshold voltage was found to be inversely related to the particle concentration and directly proportional to particle size as measured by light scattering. Accordingly, we developed an agglomeration model that accounts for the influence of particle size on the threshold voltage.