Nanoparticle orientation distribution analysis and design for polymeric piezoresistive sensors

Abstract

Piezoresistive sensors, with polymer matrices and conductive nanoparticles, are a relatively new addition to the sensor class, with the potential to transform such fields as wearable sensors and the internet of things. The unusual inverse piezoresistive behavior of the sensors has been modeled using quantum tunneling and percolation theory. However, the impact of the distribution of conductive particles in the matrix, and specifically their relative orientation, has not been well studied. The initial and deformed distribution of orientations greatly influences the sensor behavior, since the quantum tunneling model is highly sensitive to the polymer gaps between nanoparticles; the evolution of these gaps under deformation is strongly dependent upon the relative orientation of neighboring particles, and determines electron transport properties, and overall sensor response. In this paper a simple analytical model for isotropic orientation distribution and subsequent Poisson-based gap evolution is compared with a more sophisticated finite element and random resistor network analysis. The new numerical model was able to explain previously unexplained physical behavior and is used to design sensors with specific desired characteristics. The appropriateness of the previously assumed percolation behavior is also examined via the model and generalized effective medium theory.