Tough and stretchable ionic polyurethane foam for use in wearable devices

Developing tough and conductive materials is crucial for the fields of wearable devices. However, soft materials like polyurethane (PU) are usually non-conductive, whereas conductive materials like carbon nanotubes (CNTs) are usually brittle. Besides, their composites usually face poor interfacial interactions, leading to a decline in performance in practical use. Here, we develop a stretchable PU/CNTs composite foam for use as a strain sensor. A cationic chain extender is incorporated to afford PU cationic groups and to regulate its mechanical properties, whose tensile strength is up to 12.30 MPa and breaking strain exceeds 1000%, and which shows considerable adhesion capability. Furthermore, porous PU foam is prepared via a salt-templating method and carboxylic CNTs with negative groups are loaded to afford the foam conductivity. The obtained foam shows high sensitivity to small strain (GF = 5.2) and exhibits outstanding long-term cycling performance, which is then used for diverse motion detection. The strategy illustrated here should provide new insights into the design of highly efficient PU-based sensors.