Innovative Alternating Current Electrophoretic Deposition for Micro/Nanoscale Structure Control of Composites

Electrophoretic deposition (EPD) using aqueous dispersions has been widely utilized to incorporate nanomaterials into fiber-reinforced composites to modify interfacial properties and introduce multifunctionality. The use of direct current EPD (DC EPD) allows deposition at a higher rate and with lower energy consumption but has limited ability to modify the intra-bundle regions of fabric substrates due to the side effects caused by vigorous water electrolysis, including gas evolution and high pH gradients that can destabilize the dispersion. Alternating current EPD (AC EPD), with sufficiently high frequency, is capable of suppressing the water electrolysis and altering the film formation mechanisms and morphology within the reinforcing fabric. In this research, an asymmetric triangular AC waveform with a zero net DC component is applied to EPD to achieve unique carbon nanotube (CNT) structures by controlling the thickness and distribution within the fabric structure. Distinctly different CNT morphologies are created by AC and DC EPD. The influence of porous electrodes on deposition kinetics and electrical conductivity is also investigated as the open pores provide the paths to dissipate evolved gas. The in-plane and through-thickness electrical conductivities of hierarchically structured CNT/glass/epoxy composite laminates are strongly affected by the as-deposited CNT morphology, as the CNTs are the only conductive constituent in the multiscale composite. AC EPD results in substantially increased CNT integration within the intra-bundle regions of the fibers. Multiscale composites fabricated by AC EPD combined with porous electrodes exhibit up to a 2300-fold increase in through-thickness electrical conductivity, while providing similar in-plane conductivity to DC EPD. The capability of tailoring the microstructure and through-thickness physical properties makes the multiscale nanocomposites fabricated by AC EPD promising for multifunctional applications such as anisotropic heat dissipation, de-icing, lightning strike protection, and in situ sensing of strain and damage.