Alignment of nano and micron diameter carbon fillers in epoxy via electric field

This paper presents an experimental investigation on the in-situ alignment of carbon fillers spanning dual length scales via the application of an external electric field to improve the electrical and mechanical properties of filled epoxy polymers. When subjecting the fillers to an applied alternating current electric field within the un-cured, liquid epoxy resin, it was found that the carbon nanofibers (CNFs) and micron diameter, short, carbon fibres (SCFs) would align along the field direction. These epoxy composites containing the nano and micron diameter scale fibrous fillers exposed to an applied electric field exhibited an increased mode I fracture toughness, G_Ic, and DC electrical conductivity along the direction of the field. In comparison to the epoxy composites containing the randomly oriented fillers, the alignment of the SCFs and CNFs, when used separately, resulted in an improvements in the G_Ic value of 30% and 27%, respectively. However, the multi-scale reinforced epoxy composites, containing the aligned fillers, exhibited a 16-fold increase in the the G_Ic compared to the unmodified epoxy and a 39% improvement over the composite containing the randomly oriented fillers. Several key toughening mechanisms through fractographic analysis were identified. The study reveals that aligning the carbon fillers ranging from the nano and the micron length scale offers a promising route in creating multi-scale reinforced composites with greatly enhanced properties.