Session: 02-01: Multiferroics

Paper Number: 90591

90591 - Effect of Viscoelasticity on Tunneling Conduction of Piezoresistive Carbon Nanotube Polymer Composites 

Electrically conductive polymer nanocomposites, consisting of an engineering polymer and an electrically conductive nanofiller such as carbon nanotubes (CNT), offer vast design freedom for strain sensing applications. The underlying piezoresistivity of the nanocomposites that gives rise to strain sensing capability has been successfully utilized in various fields including health and motion monitoring. Piezoresistivity modeling of carbon nanotube polymer composites is critical for identifying the parameters acting their performance, but remains a challenging subject due to the complex CNT network microstructure and the contributing effects at the micro and nano scales. In this work, a computational piezoresistive model of CNT polymer composites that addresses several gaps in existing literature is put forward. First the prevailing assumptions on CNT network kinematics and tunneling conduction are examined, and their effects are studied by tracking the history of tunneling separation of each CNT junction and performing a statistical analysis of tunneling conduction evolution. Second, we investigate the role of polymer viscoelasticity on piezoresistive response. It has been observed that certain CNT polymer composite sensors suffer from hysteresis and drift under cyclic and long-term operation. Viscoelasticity of the polymer has been identified as one of the underlying causes for, but the mechanism is not well understood. The polymer is modeled as linear viscoelastic material without invoking the overly restrictive assumption of time-independent Poisson's ratio. A series of creep experiments at various temperatures has been conducted to provide multiaxial relaxation properties for the CNT polymer composites. The macroscopic piezoresistive behavior is simulated under constant strain and cyclic strain profiles to elucidate the microscopic mechanisms for drift and hysteresis in sensing performance. Results show that matrix viscoelasticity by itself causes an electrical resistance relaxation during an applied constant strain profile due to an increasing compaction of the CNT network in the transverse direction over time, leading to reduced tunneling resistance in the axial direction.  

Presenting Author: Kawai Kwok University of Central Florida