Carbon Nanotube–Polyurethane\nComposite Sheets\nfor Flexible Thermoelectric Materials

Abstract

Integration of single-wall carbon nanotubes (SWCNTs)\nin the form\nof fabriclike sheets or other preformed assemblies (films, fibers,\netc.) simplifies their handling and allows for composites with higher\nnanotube contents, which is needed to better exploit their outstanding\nproperties and achieve multifunctional materials with improved performance.\nHere, we show the development of p-type SWCNT–thermoplastic\npolyurethane (TPU) fabric materials with a wide range of SWCNT contents\n(from 5 to 90 wt %) by employing a one-step filtration method using\na suspension of SWCNTs in a TPU solvent/nonsolvent mixture. The mechanical\nand thermoelectric (TE) properties of these SWCNT–TPU nanocomposites\nwere tailored by varying the SWCNT/TPU wt % ratio, achieving significant\nadvantages relative to the pristine SWCNT buckypaper (BP) sheets in\nterms of strength and stretchability. In particular, the SWCNT–TPU\nnanocomposite with a 50/50 wt % ratio composition (equivalent to 15\nvol % of SWCNTs) shows a power factor (PF) of 57 μW m^–1 K^–2, slightly higher compared to the PF of the\nSWCNT BP prepared under the same conditions (54 μW m^–1 K^–2), while its mechanical properties significantly\nincreased (e.g., ∼7-, 25-, and 250-fold improvements in stiffness,\nstrength, and tensile toughness, respectively). These results represent\na significant step toward the development of easy-to-process self-supporting\nand stretchable materials with robust mechanical properties for flexible\nthermoelectric devices.