Full elastic constitutive relation of non-isotropic aligned-CNT/PDMS flexible nanocomposites

Abstract

The elastic response of vertically aligned-carbon nanotubes/polydimethylsiloxane (A-CNTs/PDMS) nanocomposites are presented in this study and related to the underlying aligned-CNT morphology. Multiwall carbon nanotubes (MWCNTs) at 1% Vf are embedded in a flexible substrate of PDMS to create a flexible polymer nanocomposite (PNC). The PNC properties are evaluated using scanning electron microscopy (SEM), differential scanning calorymetry (DSC), dynamic mechanical analysis (DMA) and tensile mechanical tests, and the full linearly-elastic constitutive relation established for such a PNC. The results suggest that the CNTs retain alignment after the wetting and curing of the PDMS. The PDMS is significantly modified by the reinforcing aligned-CNT fibers, demonstrating non-isotropic (as opposed to the isotropic neat PDMS) elastic properties all different than the PDMS (Young´s modulus of 0.8 MPa), including an anisotropy ratio of 4.8 and increases in the modulus of A-CNTS/PDMS over PDMS by more than 900% and 100%, in the CNTs longitudinal and transverse directions, respectively. This study reports the first full constitutive relation that may be useful in modeling PNCs as composites or as elements of hierarchical nanoengineered composites, particularly PDMS-CNTs PNCs envisioned as elements in biomedical devices such as pressure transducers and energy harvesters.