A Proof-of-Concept Study of Auxetic Composite Foams with Negative Poisson’s Ratio for Enhanced Strain-Stable Performance of Electromagnetic Shielding

Stretching of conductive polymer composite (CPC) foams always results in a severe reduction in electromagnetic interference shielding effectiveness (EMI SE) mainly due to the destruction of conductive networks and the decrement of sample thickness. Therefore, it is desirable to develop a novel strategy for preparing CPC foams with strain-stable EMI SE under moderate stretching. Herein, a strategy of constructing an auxetic structure to stabilize the EMI SE of CPC foams during stretching is proposed for the first time. Lightweight auxetic polyurethane/carbon nanotube (APU/CNT) composite foams were prepared by a solution dip-coating approach and triaxial volumetric compression. Compared with nonauxetic PU/CNT foam, the APU/CNT foam with similar filler loading and density of around 0.035 g/cm 3 showed more stable SE values with the increase of tensile strain (especially within the first 20% strain, the SE/SE 0 reduction of the APU/CNT foam is less than ∼5%), exhibiting enhanced strain-stable EMI-shielding behavior in the stretching process. The underlying reason is that the presence of auxetic structure with a negative Poisson’s ratio could not only slightly increase the thickness of the foam but also avoid the serious destruction of the conductive networks under stretching, which is beneficial to attenuate EM waves more stably. Moreover, the outstanding and more stable Joule-heating performance could also be observed in the stretched APU/CNT foam. This work reveals the potential of auxetic structures to solve the challenging problem of how to stabilize the EMI-shielding (or Joule-heating) performance of CPC foams during moderate stretching.