Mechanical-electrical characterization of carbon-nanotube thin films for structural monitoring applications

To measure component-level structural responses due to external loading, strain sensors can provide detailed information pertaining to localized structural behavior. Although current metal foil strain sensors are capable of measuring strain deformations, they suffer from disadvantages including long-term performance issues when deployed in the field environment. This paper presents a novel carbon-nanotube polymer composite thin film that can be tailored for specific strain sensing properties. Beginning at the nano-scale, molecular manipulation of single-walled carbon nanotubes (SWNT) is performed to control chemical fabrication parameters as a means of establishing a relationship with macroscale bulk sensor properties. This novel strain sensor is fabricated using the Layer-by-Layer (LbL) self-assembly process. A rigorous experimental methodology is laid out to subject a variety of thin films to tensile-compressive cyclic loading. In particular, SWNT concentration, polyelectrolyte concentration, and film thickness are varied during the fabrication process to produce a variety of strain sensors. This study correlates fabrication parameters with bulk strain sensor properties; sensor properties including sensitivity (gauge factor), linearity, and hysteresis, are explored.