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

Electrophoretic deposition (EPD) using aqueous dispersionshasbeen widely utilized to incorporate nanomaterials into fiber-reinforcedcomposites to modify interfacial properties and introduce multifunctionality.The use of direct current EPD (DC EPD) allows deposition at a higherrate and with lower energy consumption but has limited ability tomodify the intra-bundle regions of fabric substrates due to the sideeffects caused by vigorous water electrolysis, including gas evolutionand high pH gradients that can destabilize the dispersion. Alternatingcurrent EPD (AC EPD), with sufficiently high frequency, is capableof suppressing the water electrolysis and altering the film formationmechanisms and morphology within the reinforcing fabric. In this research,an asymmetric triangular AC waveform with a zero net DC componentis applied to EPD to achieve unique carbon nanotube (CNT) structuresby 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 electricalconductivity is also investigated as the open pores provide the pathsto dissipate evolved gas. The in-plane and through-thickness electricalconductivities of hierarchically structured CNT/glass/epoxy compositelaminates are strongly affected by the as-deposited CNT morphology,as the CNTs are the only conductive constituent in the multiscalecomposite. AC EPD results in substantially increased CNT integrationwithin the intra-bundle regions of the fibers. Multiscale compositesfabricated by AC EPD combined with porous electrodes exhibit up toa 2300-fold increase in through-thickness electrical conductivity,while providing similar in-plane conductivity to DC EPD. The capabilityof tailoring the microstructure and through-thickness physical propertiesmakes the multiscale nanocomposites fabricated by AC EPD promisingfor multifunctional applications such as anisotropic heat dissipation,de-icing, lightning strike protection, and in situ sensing of strain and damage.