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.