In the long evolutionary process, nature uses its ingenious and magical ways to produce lightweight, strong, and tough materials with complex, hierarchical architecture. The current natural materials such as cellulose tissues, mineralized tissues, and nacre (mother-of-pearl), have aroused special interest in material science. A popular biological model is “bricks-and-mortar” arrangement of nacre (mother-of-pearl) that consists of inorganic and organic constituents. The precise arrangement constituted of well-aligned inorganic 2D platelets surrounded by an elastic biopolymer matrix which serves as a glue by the nanoscale hydrogen-bonding (H-bonding) networks, friction, chain straightening of biopolymer and mineral bridges between the platelets, plays a critical role in a unique combination of excellent strength and toughness in nacre.
Through analyzing the advantages for outstanding mechanical performance of nacre, we attempt to design nacre-like composites both with high strength and excellent toughness. Individual GO sheets have been verified as an ideal reinforcing filler because of their light weightness, outstanding mechanical properties (Young’s modulus up to 250 GPa), high aspect ratio (~1 nm-thick-by-2.5-to-5-μm-diameter sheets), high flexibility, good ductility, and superior processability. What’s more, GO sheets consist of a hexagonal carbon network, having both sp2 and sp3-hybridized carbons, possessing a multitude of oxygen-containing functional groups on its “basal” surface, interfacial interactions with polymer matrix have been improved by numerous H-bonding networks. Sodium alginate (SA), a linear anionic polysaccharide co-polymer, which consists of two sterically different repeating units, (1→4)-α-L-guluronate (G unit) and (1→4)-β-D-mannuronate (M uint) in varying proportions Owing to its unique tissue compatibility and applications in tissue engineering, Sodium alginate has been widely investigated.
Here, we fabricated a kind of artificial nacre-like composite paper with GO/SA hybrid building blocks by vacuum-assisted flocculation (VAF). The mechanical properties obtained in natural environment (25 °C, 15 % relative humidity (RH)) are many-fold higher than the published data to date (such as several types of natural materials, composites containing SA biopolymer with different fillers and different polymeric materials with GO sheets), which achieve a unique combination of high ultimate stress (272.3 ± 13.9 MPa) and high toughness (12.5 MJ m-3, up to 18.1 ± 0.6 MJ m-3 in some cases) for the nacre-like composite paper. We suggest that the binary synergistic strengthening/toughening enhancement from both components with complementary heterogeneous nature of abundant oxygen-containing functional groups on their interfaces is promoted by the strong cooperative/H-bonding interactions. Besides, through further testing the mechanical properties under wet environment/thermal annealing of different temperature, we confirm that this nacre-like composite paper is much more suitable for application in natural environment or below 70 °C holding relative low RH. Such successful fabricated composites will have potential applications in many fields such as structural, tissue engineering, protection, aerospace, and permeable membranes for separation and delivery.
Ke Chen, Bin Shi, Yonghai Yu, Juanjuan Qi, Lin Guo
Key Laboratory of Bio-inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing 100191, People’s Republic of China
A crucial requirement for most of the engineering materials is the excellent balance of strength and toughness. By mimicking the hybrid hierarchical structure in nacre, a kind of nacre-like paper based on binary hybrid graphene oxide (GO)/sodium alginate (SA) building blocks has been successfully fabricated. Systematic evaluation for the mechanical property in different (dry/wet) environment/after thermal annealing shows a perfect combination of high strength and toughness. Both of the parameters are nearly many-times higher than those of similar materials because of the synergistic strengthening/toughening enhancement from the binary GO/SA hybrids. The successful fabrication route offers an excellent approach to design advanced strong integrated nacre-like composite materials, which can be applied in tissue engineering, protection, aerospace and permeable membranes for separation and delivery.
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Inspired by the hybrid hierarchical/bricks-and-mortar structure in natural nacre from abalone shell with excellent mechanical property, graphene oxide (GO) sheets were selected as hard “bricks” and sodium alginate (SA) was served as “mortar”, a new artificial nacre-like graphene oxide/sodium alginate composite paper was designed and fabricated by using vacuum-assisted flocculation (VAF) assembly of GO/SA hybrid building blocks. The strong cooperative/H-bonding interactions between both components are attributed to abundant oxygen-containing functional groups on their interfaces. Our composite paper has the nacre-like layered microstructure and possesses unique combination of high ultimate stress (272.3 ± 13.9 MPa) and high toughness (12.5 MJ m-3, up to 18.1 ± 0.6 MJ m-3 in some cases).