Bioinspired Hierarchical Alumina–Graphene Oxide–Poly(vinyl alcohol) Artificial Nacre with Optimized Strength and Toughness

Abstract

Due to hierarchical organization of micro- and nanostructures, natural nacre exhibits extraordinary strength and toughness, and thus provides a superior model for the design and fabrication of high-performance artificial composite materials. Although great progress has been made in constructing layered composites by alternately stacking hard inorganic platelets and soft polymers, the real issue is that the excellent strength of these composites was obtained at the sacrifice of toughness. In this work, inspired by the layered aragonite microplatelets/chitin nanofibers-protein structure of natural nacre, alumina microplatelets-graphene oxide nanosheets-poly(vinyl alcohol) (Al2O3/GO-PVA) artificial nacre is successfully constructed through layer-by-layer bottom-up assembly, in which Al2O3 and GO-PVA act as "bricks" and "mortar", respectively. The artificial nacre has hierarchical "brick-and-mortar" structure and exhibits excellent strength (143 ± 13 MPa) and toughness (9.2 ± 2.7 MJ/m(3)), which are superior to those of natural nacre (80-135 MPa, 1.8 MJ/m(3)). It was demonstrated that the multiscale hierarchical structure of ultrathin GO nanosheets and submicrometer-thick Al2O3 platelets can deal with the conflict between strength and toughness, thus leading to the excellent mechanical properties that cannot be obtained using only one size of platelet. We strongly believe that the work presented here provides a creative strategy for designing and developing new composites with excellent strength and toughness.

Strengthening of Ceramic-based Artificial Nacre via Synergistic Interactions of 1D Vanadium Pentoxide and 2D Graphene Oxide Building Blocks

“…In the resulting composites, smooth structural integration is expected due to GO’s 2D structure and the presence of oxygen-containing functional groups located on the basal planes. In contrast to previous reports242527, such a ternary system features an “inverse” composition with a small amount of soft component embedded into a comparatively harder matrix. The interaction between the different building blocks should lead to a unique combination of high tensile strength, good toughness, as well as excellent stiffness in a synergistic fashion.…”

“…The interaction between the 1D and 2D building blocks can lead to sliding effects, crack deflection and crack bridging, thereby enhancing the strength and toughness of such composite materials in a synergistic manner2122. Recently, several studies have addressed the design and mechanical characterization of ternary artificial nacre232425262728. For instance, Wang et al 24.…”

“…However, owing their comparably soft matrix material, they exhibit only a low Young’s modulus25262728. In order to achieve a ternary system that combines good tensile strength with high stiffness and form stability, designing a ceramic-based ternary system represents a promising approach.…”

Ternary Artificial Nacre Reinforced by Ultrathin Amorphous Alumina with Exceptional Mechanical Properties

“…Comparing the strength and toughness among the ternary artifi cial nacres with different AA contents, it becomes clear that a higher content of AA led to higher failure strength and higher toughness (Figure 3 b). To further verify the advantages of our novel ternary artifi cial nacres, the tensile strength and toughness of natural nacre and all GO/rGO-based nacre-inspired fi lms are summarized in Figure 3 c. [ 24,31,32,34,[38][39][40][41][42][43][44][45][46] It can be seen that the tensile strength and toughness of the ternary GO-AA-SCMC-III artifi cial nacre were 2.3-times and 4.3-times higher than that of natural nacre, [ 34 ] which only showed a tensile strength of 80-130 MPa and toughness of 1.8 MJ m −3 . On the contrary, in the binary GO/rGO-based artifi cial nacres, only one of the mechanical properties (strength or toughness) can be improved at the cost of the other.…”

“…Unfortunately, the properties of toughness and strength are mutually exclusive. Recently, researchers have demonstrated that ternary artifi cial nacres reinforced by a third reinforcement agent, such as nanofi brillar cellulose, [ 29 ] carbon nanotubes, [ 30 ] Al 2 O 3 , [ 31 ] or MoS 2 , [ 32 ] show a simultaneous increase in both strength and toughness, which makes them superior to natural nacre [ 2 ] and artifi cial binary nacre.[ 8 ] However, the random addition of a third component into the binary composites during the preparing process does not guarantee a perfect match of the third reinforcement agent with the original brick and mortar structure, thus this may lead to a limited improvement in strength and toughness.Herein, a new type of ternary artifi cial nacre (graphene oxide (GO)/ultrathin amorphous alumina (AA)/sodium carboxymethyl cellulose (SCMC)) has successfully been synthesized by a simple vacuum-assisted fi ltration method. In order to guarantee the uniform layered nacre-like structure of this new product for the fi rst time, the ultrathin amorphous alumina (AA) was grown in situ on the surface of GO with a thickness varying from around 1 nm to 10 nm before mixing this together with the polymer SCMC.…”