▎ 摘　　要

Lightweight, superelastic foams that resist creep and fatigue over a broad temperature range are being developed as structural and functional materials for use in numerous diverse applications. Unfortunately, conventional foams display superelasticity degradation, undergo considerable creep, show fatigue under repeated usage, or fracture over large strains, particularly under significant temperature variations. We report that graphene-coated single-walled carbon nanotube (SWCNT) aerogels remain superelastic, and resist fatigue and creep over a broad temperature range of -100-500 degrees C. The microstructure of these ultralow density (approximate to 14 mg/mL; corresponding volume fraction approximate to 9 x 10(-3)) aerogels is composed of a three-dimensional network of randomly oriented SWCNTs with junctions between SWCNTs coated with 2-5 layers of approximate to 3 nm long graphene nanoplatelets. Compressive stress (sigma) versus compressive strain (epsilon) curves show that the aerogels fully recover their shapes even when strained by at least 80% over -100-300 degrees C and 20% at 500 degrees C, whereas the Young's modulus remains similar over the temperature (-100-500 degrees C) and strain rate e (0.01-0.16 1/s) ranges. We suggest that under compression, the graphene layers hinder free rotation and irreversible sliding of the SWCNTS about the junctions, leading to bending of the graphene layers, while the struts form new junctions stabilized via van der Waals interactions. When the compressive load is removed, the bent graphene layers provide a restoring force that breaks the junctions created during compression, accounting for full aerogel shape recovery, albeit with hysteresis. The storage (E') and loss (E '') moduli measured in the linear regime show ultralow damping ratio (tan delta = E ''/E') approximate to 0.02, and these viscoelastic properties remain constant over three decades of frequencies (0.628-628 rad/s) and across -100-500 C. The low loss in these aerogels is corroborated by exceptional fatigue resistance for 2000 (5 X 10(5)) cycles at e = 60% (1%) from-100-300 degrees C (-100-500 degrees C) and creep resistance at least under sigma = 20 kPa, for a minimum of 1 min from -100-500 degrees C. Furthermore, these aerogels retain their exceptional creep resistance under the same creep test conditions but for much longer time of 30 min at all tested temperatures except at 500 degrees C where they show small creep epsilon of approximate to 0.7% with approximate to 0.8% residual 8. The emergent thermomechanical stability of these aerogels that arises from, in part, microscopic deformations of the graphene-coated junctions, motivate junction modification as a means to control the mechanical properties of CNT foams in general. Furthermore, the temperature-invariant mechanical properties of these aerogels combined with their facile fabrication method, which is readily applicable to other nanotube foams, make this class of aerogels a strong alternative to conventional foams, particularly in environments with large temperature variations.