The experimental measurement of effective compressive modulus of carbon nanotube forests and the nature of deformation

Measurement of the effective compressive modulus of vertically aligned carbon nanotube (CNT) forests/turfs is evaluated with two different experimental methods. The first experimental method uses a high force nanoindentation system to uniformly compress CNT forests grown on rigid silicon substrates with a second silicon substrate on the top surface of the CNTs. This is performed for CNTs with heights of 61, 315, and 683 μm. Using this nanoindentation-based method, the measured effective compressive modulus values ranged from 0.12 to 1.2 MPa. Additionally, the effect of end constraints is investigated by testing the CNT forests with and without attaching the second rigid substrate to the CNT forest tips with an adhesive. It was found that attaching the second substrate to the CNT tips with an adhesive increases the measured effective compressive modulus by 10–30%. The second experimental method in this study is semi in situ and uses a scanning electron microscope and a compressive fixture with load cell. This method shows that under uniform compressive loading, the CNT forests demonstrate a local folding form of deformation with initial folding occurring near the growth substrate. The effective compressive modulus measured using this method was 0.11 MPa for 133 μm tall CNT forests.