The effect of electrostatic and electrohydrodynamic forces on the chaining of carbon nanofibres in liquid epoxy

Abstract

The formation of chains of aligned carbon nanofibres (CNFs) in polymers is a subject of great interest in the field of multifunctional nanocomposites. The mechanism of CNF chain assembly and growth in a low viscosity epoxy is investigated by developing a finite element model of a chain attached to an electrode. The model examines the combined effects of electrostatic and electrohydrodynamic forces on chain morphology. The electrohydrodynamic forces are modelled using the theory of ac electro-osmosis. The predictions of the model are supported by experimental results. The experiments were conducted on a CNF/epoxy/amine mixture by applying an ac field at frequencies ranging from 100 to 100 000 Hz. The predictions of the model qualitatively capture the variations of chain morphology and growth rate as functions of ac frequency. Higher frequencies promote a more uniform and denser network of chains. The rate of growth of chains is highest at an intermediate frequency. A uniform network of chains was observed at frequencies of 1 kHz and greater in the experiments. The rate of growth of chains was maximized at a frequency of 1 kHz for a liquid viscosity of 0.03 Pa s.

Parallel integration of aligned carbon strings in polymer composite: Dielectrophoretic preparation, finite element simulation, and electrical characterization

“…Prasse et al and Schwarz et al were the first to align carbon black (CB) particles in an oligomer fluid followed by polymerization which locks the particles in place in a polymer matrix. In the following years the idea of aligned carbon was studied further and extended to graphite sheets , carbon nanotubes (CNTs) carbon fibres and carbon cones . Common for all these reports is the use of an initial particle fraction much below the percolation threshold of the isotropic mixture, and thus initially electrically insulating mixture, and a conductivity jump due to the aligned strings forming conductive pathways through the polymerized matrix.…”

Fabrication of a Large-Scale Conductive Composite Film Containing Electrically Aligned Carbon Nanotubes

“…A pair of parallel plate electrodes, in which the nanocomposite was sandwiched, has been widely employed for the electric field application. It has been reported that preferable electric field for CNT alignment in polymers had an intensity of 1 kV/cm in order of magnitude and a frequency as high as about 1 kHz [17,18]. Considering that the maximum output voltage of a commercially available high frequency (HF) voltage source is typically a few kilovolts, the size of nanocomposite, which is equal to the distance between parallel plate electrodes, has been limited to a few centimeters.…”