Polyurethane/polydopamine/graphene auxetic composite foam with high-efficient and tunable electromagnetic interference shielding performance

In this work, two kinds of auxetic composite foams of polyurethane (PU) with polydopamine (PDA) and graphene (GR) (PU/PDA/GR) were prepared by dip-coating and ultrasonic immersing, then followed by triaxial compression-heating process. The electromagnetic interference (EMI) shielding effectiveness (SE) value of the PU/PDA/GR auxetic composite foam with a Poisson's ratio of -2.36 from PU foam with open cellular structure reaches 59.75 dB, which is 8.9 times of the positive Poisson's ratio composite foam with the same GR content. Furthermore, the relationship of the EMI shielding performance of auxetic foam with different forms of reentrant structure was studied for the first time, in which the absolute value of negative Poisson's ratio was used to quantitatively describe the difference of the reentrant structure in the obtained auxetic foam. The larger the absolute value of negative Poisson's ratio is, the better the EMI shielding performance of the composite foam is. The high absorption EMI SE and the existence of reentrant structure are the key factors for the high EMI shielding performance of the auxetic composite foam. In addition, it is found that the EMI SE of the auxetic foam can be adjusted via simple heating treatment, showing that the auxetic composite foam may be used as a temperature-regulated EMI shielding material in the future.