Multifunctional Free-Standing Thermoelectric Nanocomposite Foams with Acoustic Properties

The thermoelectric effect (TE) represents a remarkable physical process that facilitates the direct conversion of thermal and electrical energies. This effect is notable for its inherent reversibility, and it has been extensively utilized in various technological applications, such as solid-state refrigeration/heating devices and temperature sensors. The efficacy of thermoelectric materials is fundamentally influenced by a constellation of material-dependent parameters, including electrical conductivity, thermal conductivity, and the Seebeck coefficient. The pursuit of optimal thermoelectric materials is driven by the need to achieve high electrical conductivity and Seebeck coefficient while maintaining minimal thermal conductivity. In recent times, the focus of thermoelectric research has undergone a significant shift, gravitating towards polymer-based nanocomposites as opposed to traditional semiconductor-based formulations. This trend is propelled by the inherent versatility of polymeric materials in customizing and manipulating their electrical and thermal conductivities. Furthermore, advantages such as enhanced mechanical pliability, lower fabrication costs, and improved manufacturability have been instrumental in directing the development of polymeric thermoelectric nanocomposites. The domain of engineered nanocomposites offers a platform for further refinement of material characteristics and thermoelectric efficiency. This is accomplished through the strategic integration of various micro- or nanostructures and secondary nanoparticles. Importantly, the incorporation of highly conductive fillers such as carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) is central to enhancing electrical conductivity. Utilizing their high aspect ratios, a small concentration of these fillers can significantly alter the overall conductivity at the macroscale, predicated on the formation of a strong interconnective conductive network within the nanocomposite matrix. Additionally, the incorporation of microstructures into the nanocomposite framework provides avenues for modulating thermal conductivity. For example, introducing cellular structures can substantially hinder thermal transfer, thereby enhancing thermoelectric performance. This research is at the vanguard of innovation, presenting a novel fabrication methodology for thermoelectric nanocomposite foams. This technique employs thermally responsive expandable microspheres integrated with thermoplastic polyurethane (TPU)-coated CNT structures. Empirical results from this study highlight the effectiveness of this approach, showcasing the production of nanocomposites with exceptional electrical conductivity. Notably, the thermal conductivity of these nanocomposites is on par with that observed in aerogel-based nanocomposites, indicating a promising pathway for developing highly efficient polymer-based thermoelectric materials with broad technological ramifications. We also evaluated the compressive stiffness, mechanical stability, and potential for sound absorption of the nanocomposite foam. With this unique combination of thermoelectric, sound absorption, and mechanical properties, the engineered thermoelectric foams show great potential for aerospace applications, where high-temperature gradients and mechanical vibration/noise are prevalent simultaneously. This research is at the vanguard of innovation, presenting a promising pathway for developing highly efficient polymer-based thermoelectric materials with broad technological ramifications.