ELECTROMECHANICAL PROPERTIES OF POLYMER NANOCOMPOSITES CONTAINING PERCOLATED CARBON NANOMATERIAL NETWORK WITH CONTROLLED NANOSTRUCTURE AND INTERFACE

Abstract

Strain-induced resistance change, known as piezoresistivity, is one of the unique characteristics of carbon-nanomaterial-filled polymer composites and makes them a potential candidate for strain sensors. This electromechanics-based strain sensing mechanism has received much attention recently due to the distinct combined advantages provided by polymers and the percolated network formed by carbon nanomaterials. Despite the merit of distributed sensing behavior, most of the previous studies have focused on small-area, one-dimensional strain sensing. In order to overcome these limitations, we conducted our research on the aims at studying and developing a multi-faceted approach to enable distributed, large-area, multi-directional strain sensing and to “tailor” the sensing performance by controlling the following factors: (1) carbon nanomaterial geometry and hybridization; (2) carbon nanomaterial-polymer interface; and (3) microstructures including porosity, alignment and micro-domain. The effects of carbon nanomaterial geometry on piezoresistivity could be best captured by studying the electromechanical behavior of carbon nanotube buckypapers, graphene sheets, and carbon nanotubes-graphene hybrids, as they enable “isolation” of the percolated carbon nanomaterial network. The strain sensing behavior of polymer-impregnated carbon nanomaterial sheets were also studied, which provided additional advantages of highly loaded nanocomposites and easy material handling. Reduced graphene oxide was selected and coated on a polymer substrate, which enabled 2D distributed conductive network and allowed tailored sensitivity based on the interfacial strength controlled by the reduction method. A further study about interfacial bonding discussed on the effects of polydopamine-functionalized reduced graphene oxide dispersed in poly(vinyl alcohol), which served as a conductometric humidity sensor. At the same time, polydopamine functionalization resulted in remarkable simultaneous improvements in tensile modulus, strength, and percent elongation, which suggests enhanced interfacial strength as well as matrix reinforcement. Finally, the piezoresistivity of highly porous nanocomposites were investigated using graphene oxide hydrogels with controlled pore size and distribution. This self-assembled 3D architectures allowed tailoring of strain sensitivity and served as a potential alternative solution that can replace conventional pressure, vibration sensors commonly used for structural health monitoring. The conducted study covered a comprehensive approach to develop carbon-nanomaterial-enabled smart sensors, encompassing materials design and processing, understanding of the underlying physics, and applications for wide-area sensing. This is unique and significant research that bridges the gap between the exceptional properties of nano-scale materials and macro-scale sensing systems. It is anticipated that the outcome of the proposed research will make inroads into application areas where large-area strain sensing and intelligent structural health monitoring, enabled by distributed sensor network with tailored accuracy and sensitivity, are required, including aerospace, automotive, civil structures, wind turbines, and nuclear power plants.