Lightweight, porous, stretchable nanocomposite foams with sandwich-like and bimodal cell structure by supercritical fluids-assisted processing for flexible strain sensor

Developing strain sensors with wide detection range and high sensitivity at a low conductive nanofillers content still faces challenges. Herein, thermoplastic polyurethane (TPU)/multi-walled carbon nanotubes (MWCNTs) nanocomposite foams with a multilayer alternating and bimodal cell structure is prepared by stacking hot pressing and supercritical carbon dioxide batch foaming process. Consequently, the synergistic effect of sandwich-like and bimodal cell structure endows the foam sensor of FTPU-C3-L10 T80P10 (TPU/3 wt%MWCNTs nanocomposite foams with ten layers alternating structure foamed at 80 ℃ and 10 MPa) 0.34 vol% MWCNTs loading, broad response range of 0–150 %, high sensitivity with a gauge factor (GF) of 101, fast response speed of 180 ms, as well as cyclic reproducibility and durability of 1000 cycles. Furthermore, the fabricated foam sensor can effectively monitor basic human motion from tiny to large. This work provides a facile strategy for designing and producing strain sensors applied in various fields, including human motion detection, artificial intelligence devices, and medical diagnosis.