Surfactant-modified multiscale composites for improved tensile fatigue and impact damage sensing

This paper documents the mechanical and electrical performance of self-sensing conductive polymer composites prepared with a low-cost technique and small hardware, able to considerably improve the dispersion and the surface adhesion of multi-walled carbon nanotubes (CNTs) in epoxy resin with respect to amine-modified CNTs and as-received CNTs. Surface treatment of the CNTs is performed using hexamethylene diamine, or a mix of sulfuric and nitric acid, and one of two surfactants (for the diamine treatment only): Triton X-100 (non-ionic) and cetyl pyridinium chloride, CPC (cationic). The effects of the treatments are shown in terms of the changes in mechanical properties and interpreted with the use of SEM, FTIR and XRD analyses. Moreover, a key and novel aspect of this work is that the improvements in dispersion and surface adhesion cause improvements of damage sensing capability under fatigue and impact. This was demonstrated on fiberglass-reinforced panels prepared with treated CNT/epoxy through hand lay-up. This study reveals that the diamine/CPC- based configuration is superior, due to improved mechanical performance, higher resistance to fatigue and impact damage (over 30 J) and increased damage sensitivity.