Super‐Compressibility of Ultralow‐Density Nanoporous Silica

Ultralight, ultrastiff mechanical metamaterials

“…However, the degradation in mechanical properties can be drastic as density decreases (17,18). A number of examples among recently reported low-density materials include graphene elastomers (19), metallic micro-lattices (20), carbon nanotube foams (21), and silica aerogels (22,23). For instance, the Young's modulus of low-density silica aerogels (22, 23) decreases to 10 kPa (10 -5 % of bulk ) at a density of less than 10 mg/cm 3 (< 0.5% of bulk).…”

“…For instance, the Young's modulus of low-density silica aerogels (22,23) decreases to 10 kPa (10 -5 % of bulk ) at a density of less than 10 mg/cm 3 (< 0.5% of bulk). This loss of mechanical performance is because most natural and engineered cellular solids with random porosity, particularly at relative densities less than 0.1%, exhibit a quadratic or stronger scaling relationship between Young's modulus and density as well as between strength and density.…”

Heavy-ion-induced modification of structural and mechanical properties of carbon-nanotube aerogels

“…[26][27][28][29] This apparent inconsistency could be reconciled by noting that, in addition to the properties of the material forming aerogel nanoligaments (i.e., CNT bundles decorated and cross-linked by graphitic nanoparticles in the the case of CNT-CAs), mechanical properties of aerogels are determined by the monolith density as well as by the geometry, size, and network connectivity of nanoligaments. [11][12][13][14][15]25 The irradiation-induced improvement in E revealed by Figs. 1 and 2(a) could be related to the formation of new crosslinks between adjacent ligaments as a result of irradiation.…”

“…12 Assumptions of such an analysis include (i) a frictionless contact and (ii) that Hertzian cracks form at the contact radius. Note that ε f sphere should be considered as a useful fracture parameter (that scales linearly with R crack ), 25 without any implicit correlation of such ε f sphere with components of the strain tensor distributions under the indenter tip. Indeed, the Hertzian analysis is valid only in the regime of small elastic deformations, while the CNTCAs studied here develop Hertzian cracks for contact radii comparable or even larger than the radius of the indenter.…”

“…25 Shown in the inset in Fig. 2(e) is a SEM image illustrating typical Hertzian ring cracks on a sample bombarded with Xe ions to a fluence of 5×10 15 cm −2 and then indented with a spherical tip (with a radius of 496 µm) to a maximum load of 500 mN.…”