A Comparison of Mechanical and Electrical Properties in Hierarchical Composites Prepared using Electrophoretic or Chemical Vapor Deposition of Carbon Nanotubes

Two approaches have been employed in the preparation of hierarchical composite laminates with a carbon nanotube (CNT) phase. Glass fibers were coated with CNTs using electrophoretic deposition (EPD) prior to infusion with epoxy resin. The CNTs were functionalized using an ultrasonicated-ozone process followed by reaction with polyethyleneimine (PEI) to enhance CNT to fiber and matrix adhesion. Chemical vapor deposition (CVD) was also used to grow CNTs onto quartz fibers, prior to infusion with an epoxy resin modified with a thermoplastic nanophase. The mechanical performance of the two CNT laminates types were similar, however, the fracture surfaces indicated distinct differences. The EPD laminates showed fracture in the CNT-rich interphase region, whereas, the CVD laminates showed that strength was limited by adhesion failure at the CNT-fiber interface. The electrical conductivity of CVD laminates was 100 times higher than EPD laminates. For the EPD laminates the PEI functionalization increases the CNT-CNT distance resulting in reduced conductivity, while the high CNT packing density and residual iron catalyst on the fiber surface in the CVD laminates creates conducting pathways resulting in higher conductivities.