Conductive Nanocomposites for Multifunctional Sensing Applications

Abstract

Over the past 20 years there has been a tremendous expansion in the development of nanostructured composite systems with engineered material properties. Nanomaterials, such as carbon nanotubes (CNTs), graphite nanoplatelets, and graphene, have been utilized widely to improve mechanical properties of polymer matrices. Because these materials are both electrically and thermally conductive, they simultaneously alter the physical properties of the polymer matrix. These nanostructured materials can have high aspect ratios – length/diameter for nanotubes and length/thickness for graphite and graphene nanoplatelets – which facilitates the formation of electrically conducting pathways in the polymer matrix. The nanocomposite electrical conductivity is dominated by electrical contact resistance between reinforcements. As a result, the nanocomposite conductivity is sensitive to external stimuli such as applied stress or temperature. These electrically conductive networks enable the use of these nanostructured composites as sensors for detecting strain, damage, and thermal transitions in situ. In addition, nanoscale reinforcements are substantially smaller than traditional advanced fibers used in composites. For example, carbon fibers have diameters on the order of 10 µm, while multi-walled carbon nanotubes (MWCNT) have typical diameters around 10 nm – three orders of magnitude smaller. The electrically conductive pathways can be formed around the structural fiber reinforcement, enabling a nerve-like network for sensing of strain and microscale cracks. This chapter highlights the constituent materials, processing approaches, and emerging applications in nanocomposites for sensing and structural health monitoring (SHM).