Lessons from Nature for Carbon‐Based Nanoarchitected Metamaterials

Abstract

Graphene, the classic one-atom-thick two-dimensional (2D) material with hexagonal lattice of sp 2 -bonded carbon atoms (a carbon atom bound to three atoms is sp 2 hybridized. When carbon is bonded to four other atoms, the hybridization is sp 3 ), was first theoretically discovered by Wallace [1] in 1947 and then was experimentally realized around 1970s. [2,3] Another form of carbon atoms, known as onedimensional (1D) carbon nanotube (CNT), was uncovered later in 1991 [4] and reported to be made out of a single graphene layer later in 1993. [5,6] Since being discovered, these carbon-based materials have attracted intensive research interest due to their outstanding thermo-electromechanical properties. [7][8][9][10][11] For instance, the monolayer graphene exhibits a unique combination of ultrahigh mechanical properties (Young's modulus of %1 TPa and tensile strength of %130 GPa [10] ), high thermal conductivity (3000-5000 W m À1 K À1 for suspended monolayer graphene), [8,12] and high electrical conductivity (10 4 to 10 5 S m À1 ). [13,14] The unique properties of graphene and CNT make them exciting candidates in flexible electronic devices, [15,16] nanosensors, [17] complementary metal-oxidesemiconductor, [11] and nanoelectromechanical systems (NEMS). [18] Nevertheless, some of CNT's and graphene's intrinsic properties, such as the limited stretchability (%0.2) [19,20] and low dimensional (1D and 2D) features, [21] can hamper their applications.By introducing rationally designed underlying architectures as the constitutive unit cell, architected materials, so-called metamaterials, with unparalleled multiphysical properties can be developed at multiple scales, from nano to macro. [22][23][24][25][26][27][28][29] For example, 3D nanoarchitected pyrolytic carbon exhibits extreme energy dissipation, which is %70% superior to that of Kevlar composites and nanoscale polystyrene films, owing to its material architecture and nanoscale material size effects. [23] Recent advances in additive manufacturing (AM) have emerged as a frontrunner for the fabrication of architected metamaterials to construct arbitrary complex architectures in a wide range of length scales. For instance, the feature resolutions of the architectures can be below 100 nm by utilizing photolithography. [30] Hence, to fully leverage these new manufacturing techniques, it is essential to design and computationally optimize materials architectures at different length scales, especially nano-and atomic scales, to achieve desired properties. Two main strategies to date have been utilized to construct nanoarchitected metamaterials based on graphene sheets and CNTs by computational simulations.

Origami Metamaterials Enable Low-Stress-Driven Giant Elastocaloric Effect

“…The high thermal conductivity ensures high heat transfer efficiency, which is a crucial indicator of caloric material performance. Previous research has indicated that surface-functionalization-induced creases can hinder the heat transport in graphene origami due to the phonon scattering. , However, thanks to the ultrahigh thermal conductivity of pristine graphene, the thermal conductivities of GMO characterized by w = 5 × c Å are around 28.94 and 96.47 W m –1 K –1 in the two in-plane directions, which are higher than those of previously reported mC materials that are typically below 10 W m –1 K –1 …”

“…Previous research has indicated that surfacefunctionalization-induced creases can hinder the heat transport in graphene origami due to the phonon scattering. 29,30 However, thanks to the ultrahigh thermal conductivity of pristine graphene, the thermal conductivities of GMO characterized by w = 5 × c Å are around 28.94 and 96.47 W m −1 K −1 in the two in-plane directions, 32 which are higher than those of previously reported mC materials that are typically below 10 W m −1 K −1 . 6 Origami engineering introduces a versatile platform for designing multifunctional and multiscale metamaterials with exceptional eC effects.…”

“…For example, the adiabatic temperature change of CNT nanotubes can be up to 30 and 65 K for applied tensile strains ε = 0.03 and 0.09, respectively . Importantly, the eC effects observed in these nanomaterials do not rely on phase transitions, thereby eliminating the hysteretic losses. , Progress in synthesis, characterization, and manipulation of low-dimensional materials has led to the identification of alternative nanomaterials, such as transition metal dichalcogenides, hexagonal boron nitride, noble metal dichalcogenides, MXenes, and metal–organic frameworks. ,, Advancements in synthesis techniques (e.g., oxygen plasma mechanical exfoliation, salt-assisted chemical vapor deposition, and pulsed laser deposition) along with computational simulation techniques (e.g., molecular dynamics (MD) , and first-principles calculations) have significantly propelled forward the studies in this cutting-edge research topic. However, persisting challenges associated with their chemical stabilities, scalability, processability, and durability have hindered their practical applications and the transition from the laboratory to market. − For example, graphene and CNT that exhibit excellent mechanical and thermal properties at the nanoscale have found to have difficulty in retaining their properties at larger scales. , Despite computational studies predicting excellent mechanical, thermal, , and electrical characteristics ,, for the low-dimensional materials, their fabrication process remains onerous.…”

“…Hence, further experimental and theoretical efforts are crucial to resolve these challenges. Concerning the eC properties, the low-dimensional materials also face intrinsic challenges, such as their brittleness (limited elasticity leads to a failure strain smaller than 0.3) ,,, and low-dimensional nature, which impede the application of their caloric characteristic in cooling systems . For instance, stretchability limitation can restrict the intrinsic caloric response, particularly in the case of materials where caloric effects are stimulated by applying mechanical strains .…”

Dragonfly‐Inspired Wing Design Enabled by Machine Learning and Maxwell's Reciprocal Diagrams

“…Engineers, scientists, and designers have long been inspired by the morphological and mechanical properties of natural/biological structures and used them in the design of next generation of advanced materials and structures in various scales. [2,3] The dragonfly wing is an example of a high-performance, lightweight structure, providing a repository of design inspirations. [4][5][6][7] Various properties of dragonfly wings have been studied previously that may fall into the following main categories: (i) the morphological properties including geometric descriptions and the microstructures of the materials of the veins and surface patches with a focus on the structural properties of the joints; [10][11][12][13][14][15]8,9] (ii) mechanical and aerodynamic performance of the wing including the assessment of the behavior of the wing under different loading conditions; [16][17][18][19][20][21][22]5] and, (iii) the biological and material properties of the wing particularly in terms of recording the structural parameters of artificial wings under specific loading conditions and the materialization of designs related to advanced materials inspired by the microstructures of the dragonfly wing.…”