Electrophoretic Deposition of Graphite Oxide on Additively Manufactured Porous Non-Conductive Thermoplastic Composites

Composite-based additive manufacturing (CBAM) is a novel sheet lamination-based additive manufacturing (AM) process that facilitates the rapid production of high-modulus, high-strength fiber-reinforced thermoplastic composites. However, CBAM-produced parts exhibit high porosity and a relatively rough surface, which limit their use in demanding engineering applications. While polymer powder coatings mitigate these effects, the conventional application method struggles to achieve uniform surface quality, underscoring the need for advanced surface treatment approaches. Electrophoretic deposition (EPD) is an advanced coating method to deposit conformal coating on such complex geometries. However, the traditional EPD methods are only suitable for electrically conductive substrates. Therefore, the non-conductive nature and non-connected porosity of CBAM-fabricated glass fiber/nylon-12 (GF/PA12) composites pose a challenge in adopting the established EPD method. This study aims to develop an anodic EPD system of graphite oxide (GO) flakes suspended in deionized water on CBAM-fabricated GF/PA12 composites by utilizing their inherent porosity. A field-assisted capillary trapping mechanism was demonstrated by employing a flush-mounted anode configuration, where the electric field concentrates within liquid-filled surface pores to drive the deposition of GO particles. A comprehensive parametric study was performed to identify appropriate EPD process parameters by varying suspension pH, concentration, applied voltage, and deposition time. The results reveal that suspension stability is the governing factor; adjusting the GO suspension to neutral pH (~7.1) and lower (0.5 g/L) concentrations reduced blockage at pore entry regions and enhanced electrophoretic migration into surface pores. This study, for the first time, demonstrated a viable pathway to apply EPD to porous, non-conductive fiber-reinforced composites in future engineering applications.