Modeling the effect of agglomeration and segregation of carbon nanotubes on the piezoresistive response of polymer nanocomposite architected materials

Polymers filled with carbon nanotubes (CNTs) are nanocomposites used for strain sensing applications as they exhibit piezoresistivity. Architected materials possess unusual behavior that can be exploited for multifunctionality. Architected materials have been fabricated using nancomposite materials to develop multifunctional sensors. However, CNT dispersion may affect positively or negatively the electrical properties of the composite. Agglomeration typically reduces electrical conductivity, and segregation usually results in increased conductivity. This in turn affects the piezoresistive response. Because of this, a micromechanics model for the piezoresistivity of CNT nanocomposites is developed. This model is used to study the effects of CNT agglomeration and segregation on the piezoresistive response of architected materials, where high aspect ratio CNTs in a polylactic acid matrix are considered as a test case. Re-entrant (auxetic) and hexagonal (non-auxetic) two-dimensional lattices were studied. Finite element simulations are performed using the micromechanics model to obtain the piezoresistive response and gauge factor of the lattices. Hexagonal lattices were found to be more sensitive to strain changes than re-entrant lattices. In the case of segregation, higher sensitivity was found for lattices with higher CNT content. For agglomeration, it was found that lattices with lower CNT content exhibited higher sensitivity to strain.