Graphene-Coated Carbon Nanotube Aerogels Remain Superelastic while Resisting Fatigue and Creep over −100 to +500 °C

Abstract

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 °C. The microstructure of these ultralow density (≈14 mg/mL; corresponding volume fraction ≈9 × 10 −3 ) aerogels is composed of a three-dimensional network of randomly oriented SWCNTs with junctions between SWCNTs coated with 2−5 layers of ≈3 nm long graphene nanoplatelets. Compressive stress (σ) versus compressive strain (ε) curves show that the aerogels fully recover their shapes even when strained by at least 80% over −100−300 °C and 20% at 500 °C, whereas the Young's modulus remains similar over the temperature (−100−500 °C) and strain rate ε̇(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 δ = E″/E′) ≈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 × 10 5 ) cycles at ε = 60% (1%) from −100−300 °C (−100−500 °C) and creep resistance at least under σ = 20 kPa, for a minimum of 1 min from −100−500 °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 °C where they show small creep ε of ≈0.7% with ≈0.8% residual ε. 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.

Wood‐Derived Lightweight and Elastic Carbon Aerogel for Pressure Sensing and Energy Storage

“…Lightweight and elastic carbon material is one of the most important candidates for developing high‐performance flexible and wearable energy storage and sensing devices owing to its various advantages, including thermal and chemical stability, low density, and high electrical conductivity 3,4. In recent years, a series of elastic carbon aerogels with low density and high porosity has been synthesized from nanocarbons such as graphene,5–7 graphene oxide (GO),8,9 carbon nanotube (CNT)10–12 or their composites 13–15. These carbon aerogels show good mechanical robustness, elasticity, and high conductivity, demonstrating their important applications in wearable sensors, electronic skins, and flexible energy storage devices.…”

Vibration Damping of Carbon Nanotube Assembly Materials

“…For example, by infiltrating pre‐formed CNT gels with a low molecular‐weight polyacrylonitrile (PAN) polymer and then critical‐point drying, a PAN/CNT composite gel can be obtained. After degassing at 140 °C, stabilizing at 210 °C, and pyrolyzing at 1010 °C, these gels can be converted into graphene‐coated gels, with the mass density increased from 8.8 to 14.0 mg cm −3 . The pure CNT gels usually collapse upon high compression ratio, for example, >90%, while the graphene‐coated gels can well recover their original shape (Figure a).…”

“…For these CNT gels, temperature‐invariant viscoelasticity has become a common feature, different from traditional viscoelastic polymers, which degrade in performance at elevated temperatures. This is because CNTs can withstand high temperatures without any significant degradation .…”

Reduced graphene oxide-based highly sensitive pressure sensor for wearable electronics via an ordered structure and enhanced interlayer interaction mechanism

“…Carbon aerogels have been fabricated via various methods including solvent thermal 8 or hydrothermal treatments, 9,10 chemical vapor deposition (CVD), 11 templating, 12 and freezecasting. 13 Rational design of microstructure is an attractive research approach for improving the mechanical properties of carbon aerogels.…”