Negative-Poisson-Ratio polyimide aerogel fabricated by tridirectional freezing for High- and Low-Temperature and Impact-Resistant applications

Although various developed materials with a negative Poisson’s ratio have been inspired by nature, the preparation of a negative-Poisson-ratio polyimide (PI) aerogel has been difficult because of its inherent structural limitations. These limitations have hindered the expansion of potential PI applications. We developed a tridirectional freezing method to prepare a superelastic PI aerogel with an ultranegative Poisson’s ratio. Through dynamic observation, the PI aerogel with a herringbone-tape frame structure exhibited an anisotropic negative Poisson’s ratio along three orthogonal axes. The maximum negative Poisson’s ratio was –0.79. Combined with a finite-element simulation, the formation mechanism of the large ultranegative Poisson’s ratio was investigated. The special internal structure provided the PI aerogels with high fatigue resistance under 10,000-cycle compression at 50% strain, and resilience under the strong impact of a metal ball. The intrinsic thermal stability of the PI provided the aerogel with a striking stability under cyclic compression at 130 °C or –100 °C ambient temperature. Our study provides a practical route for designing superelastic, ultranegative-Poisson-ratio polymer aerogels for applications in strong-impact and high- or low-temperature environments.