The growing interest in the fabrication of flexible nanocomposite sensors, along with the limitation of current technologies, prompted us to develop new types of nanocomposite foam structures that possess high sensitivity, repeatable piezoresistive behavior, ultra-flexibility, high compressibility, and high mechanical properties. In this context, a comprehensive study that investigates the effect of various polymer matrices, conductive filler contents, foam porosity, foam morphology, and different manufacturing methods on the piezoresistivity, sensitivity, and mechanical properties of nanocomposite foams was conducted. Moreover, for a better understanding of porous and nonporous nanocomposites’ mechanical behavior, micromechanical modeling approaches were used to predict their elastic modulus.

The first phase of this research work was focused on the fabrication and characterization of mechanical and electrical properties of polydimethylsiloxane (PDMS)/multi-walled carbon nanotube (MWCNT) nanocomposite foams. Eshelby-Mori-Tanaka (EMT) and Halpin-Tsai (HT) micromechanical approaches and extended Gibson and Ashby’s approach were applied to theoretically predict the elastic modulus of nonporous and porous PDMS/MWCNT. The results indicated that optimal porosity (60%) and MWCNT content (0.5 wt.%) could guarantee improvement in pressure sensitivity and Young’s modulus of PDMS/MWCNT nanocomposite foams.

In the second phase, we focused on the fabrication of thermoplastic polyurethane (TPU) based closed-cell nanocomposite foams through different cost-effective scalable manufacturing methods. Porous TPU/MWCNT nanocomposites foamed by implementing a chemical blowing agent (CBA) into the nanocomposite matrix through combined compounding-compression molding methods, demonstrated high elastic modulus (up to 6.2 ± 0.6 MPa) and compressibility (up to 68.5% compressive strain). According to the theoretical approaches, different modifications of HT employed in solid TPU/MWCNT, and Gibson and Ashby’s method employed in foam TPU/MWCNT were in good agreement with experimental results in predicting elastic modulus. To improve MWCNT dispersion, TPU/MWCNT nanocomposite foams were fabricated by solvent casting method using thermo-expandable blowing agents. The cyclic mechanical testing showed a repeatable piezoresistive behavior and deformation in each cycle with constant hysteresis for these materials. Results indicated that higher MWCNT and blowing agent contents reduced the electrical resistance of nanocomposite foams;​ however, in response to the compression deformation and formation of new conductive pathways, an optimum level of both parameters was necessary to meet higher pressure sensitivity.