Mechanical characterization and modeling of three-dimensional carbon nanotube structures

The exceptionally mechanical properties reported for carbon nanotubes (CNTs) has stimulated the research in the development of three-dimensional (3D) CNT based architectures (i.e. sponges, foams and aerogels). The production of engineered 3D CNT structures, with controlled architecture, are predicted to be one of the most desirable steps for building next-generation carbon-based functional materials. Before these predicted extraordinary properties at the nanoscale are realized in macroscale, considerable characterization and modeling research is necessary. This research work seeks to obtain a fundamental understanding of the mechanical properties and ultrastructure-property relations in 3D CNT materials and their composite through integrated mechanical characterization as well as development of constitutive model for the elastic properties of 3D CNTs. Ultimately, the characterization results and the establishment of structure-property relationships will guide the future design of 3D CNT materials. In this work, systematical mechanical characterization, especially for the viscoelastic properties, was performed on the three types of 3D multiwalled CNTs (MWNT) sponge. The as-fabricated materials includes 3D boron doped MWNT (CBxMWNT), nitrogen doped MWNT (N-MWNT) and undoped-MWNT sponge. The doping strategy during the fabrication of CBxMWNT and N-MWNT generates the covalent junctions between CNTs and differentiate their ultrastructure from that of undoped-MWNT. Based on mechanical and microscopic characterization results, a microstructure informed continuum constitutive modeling was developed to describe the hyperelastic behavior of 3D CNTs with covalent junctions and their structure-property relationships. To further reveal the application of 3D CNT sponge, 3D CNT reinforced polydimethylsiloxane composites were synthesized and fabricated. The effective reinforcement modulus of 3D CNT inside the composite was estimated.