Mechanical testing and modelling of a vertically aligned carbon nanotube composite structure

Recent advances have shown effective reinforcement of a polymer matrix using vertically aligned carbon nanotube (VACNT) forests grown using chemical vapour deposition (CVD). Such structures are known to wet readily through capillary interactions to form fully wetted composites that retain the dispersion and alignment of the CNT within the matrix thus overcoming two major problems in CNT composite production. So far VACNT composite fabrication has been limited by available forest size and as a result mechanical characterisation of such materials has been restricted and has generally been conducted using nanoindentation techniques. In this work VACNT composite samples are produced that are of a sufficiently large size to conduct Dynamic Mechanical Thermal Analysis (DMTA) in single cantilever mode allowing macroscale testing of the complete composite sample. Results from experiments are compared to current VACNT composite modelling techniques that consider CNT waviness which is known to exist within such composite samples. Previously the effects of as grown VACNT waviness have been considered detrimental to the overall mechanical properties of these novel composites as analysis has typically been conducted in the axial direction where applied load and VACNT axis are parallel. In this work a positive effect on sample modulus resulting from VACNT waviness has been found in the transverse plane, perpendicular to the CNT axis. Specifically an increase in modulus of over 20% is observed with only a 2 vol.% CNT loading and is in agreement with wavy CNT composite modelling.