Multifunctional polydimethylsiloxane foam with multi-walled carbon nanotube and thermo-expandable microsphere for temperature sensing, microwave shielding and piezoresistive sensor

[Display omitted] •Multifunctional elastomer foams were achieved by thermos-expandable microspheres.•Piezoresistivity of foams was improved by adding thermos-expandable microspheres.•The foams showed distinguishing signal response, reliability and stability.•The unfoamed composites showed NTC first and then PTC, finally NTC again.•Microwave shielding was greatly improved by adding thermos-expandable microspheres. In this work, the multifunctional elastomer foam with robust mechanical properties, highly piezoresistive sensitivity, special temperature-sensitive characteristic and excellent EMI shielding property was successfully fabricated by directly introducing thermo-expandable microspheres (EM) into polydimethylsiloxane/multi-walled carbon nanotube (PDMS/CNT). It was found that the addition of EM enhanced the piezoresistivity, integrating the properties of quick response (60 ms), excellent reliability and extraordinary stability. For example, the value of I/I0 in the PDMS/EM/CNT composites with 30 wt% EM and 1.0 wt% CNT achieved 1800% enhancement compared to the composites without EM. Besides, the self-reinforced PDMS/EM/CNT elastomer with unique softening behavior showed great potential in strain alerting device. Moreover, the special temperature-sensitive sensing in the unfoamed PDMS/EM/CNT sample was studied in detail, exhibiting the NTC effect first, and then PTC effect, finally NTC again. Furthermore, the EMI shielding performance got incredible improvement due to the introduction of multiple interfaces and the enhancement of conductivity. For example, by incorporating 10, 30 and 50 vol% EM into the PDMS/CNT composites, the improved EMI SE of ~32, ~36 and ~43 dB were gained, respectively.