Nacre (mother-of-pearl), made of inorganic and organic constituents (95 vol% aragonite calcium carbonate (CaCO(3)) platelets and 5 vol% elastic biopolymers), possesses a unique combination of remarkable strength and toughness, which is compatible for conventional high performance materials. The excellent mechanical properties are related to its hierarchical structure and precisely designed organic-inorganic interface. The rational design of aragonite platelet strength, aspect ratio of aragonite platelets, and interface strength ensures that the strength of nacre is maximized under platelet pull-out failure mode. At the same time, the synergy of strain hardening mechanisms acting over multiple scales results in platelets sliding on one another, and thus maximizes the energy dissipation of viscoplastic biopolymers. The excellent integrated mechanical properties with hierarchical structure have inspired chemists and materials scientists to develop biomimetic strategies for artificial nacre materials. This critical review presents a broad overview of the state-of-the-art work on the preparation of layered organic-inorganic nanocomposites inspired by nacre, in particular, the advantages and disadvantages of various biomimetic strategies. Discussion is focused on the effect of the layered structure, interface, and component loading on strength and toughness of nacre-mimic layered nanocomposites (148 references).

Inspired by the layered aragonite platelet/nanofibrillar chitin/protein ternary structure and integration of extraordinary strength and toughness of natural nacre, artificial nacre based on clay platelet/nanofibrillar cellulose/poly(vinyl alcohol) is constructed through an evaporation-induced self-assembly technique. The synergistic toughening effect from clay platelets and nanofibrillar cellulose is successfully demonstrated. The artificial nacre achieves an excellent balance of strength and toughness and a fatigue-resistant property, superior to natural nacre and other conventional layered clay/polymer binary composites.

Due to low density, extremely high electrical and thermal conductivities, graphene has great potential to construct lightweight thermal conductive paper for high-power electric devices. However, the remarkable properties of graphene are on a molecular level and difficult to achieve when processed into macroscopic paper. Here, an effective route to construct ultrahigh conductive graphene paper is developed. First, large-volume, high-concentration, planedefect-free, few-layer graphene dispersion is fast produced from graphite at high yield through ball milling. The exfoliated graphene dispersion is further processed into graphene paper through fast filtration, thermal treatment, and mechanical compression. The electrical and thermal conductivities of the resultant graphene paper are as high as 2231 S cm −1 and 1529 W m −1 K −1 , superior to previously reported graphene papers. Structural analyses confirm that the ultrahigh conductivities are attributed to high quality of graphene sheets, their compact ordered stacking, and large graphitic crystalline domain size, which improve electron and phonon transport within basal plane of graphene sheet and between graphene sheets.

The demand for robust hydrogels in pharmaceutical, biomedical, and industrial applications has motivated intense research efforts in these wet polymeric materials. [1] Recent advances have resulted in different strategies for creating highly stretchable polymeric hydrogels, including sliding-ring gels (SR gels), [2] nanocomposite gels (NC gels), [3] doublenetwork gels (DN gels), [4] macromolecular microsphere composite gels, [5] and tetra-poly(ethylene glycol) gels. [6] Among them, NC gels have attracted significant interest because of the simplicity of synthesis, high transparency, impressive mechanical properties, large reversible deformation, and excellent swelling and stimuli sensitivities. [7] The high mechanical properties of NC gels are desirable for practical application in many fields. However, it remains a great technical challenge to improve mechanical properties by enhancing the content of inorganic composition. Only a few percent of inorganic clay can be incorporated into NC gels (< 12 wt % at most), even though special mixing or modification of clay are adopted. [8] Further incorporation of clay leads to opacity and lower mechanical properties than the expected theoretical values resulting from the insufficiency of the nanoplatelet dispersion at high viscosity.As natural inorganic-organic nanocomposites, nacre finds its way around this problem by developing a well-ordered brick-and-mortar microstructure and robust interface. [9] Although mostly made of mineral platelets, nacre possesses an excellent combination of elastic modulus, strength, and toughness [10] and it provides a prime microstructural design model for the development of new materials. Recently, the layered microstructure of nacre has been successfully mim-icked and nacrelike hard structure materials with high mechanical performance were fabricated. [11] As for soft, wet inorganic-organic composites, NC gels can also benefit from duplication of the micro-/nanoscale structures of nacre. Herein, inspired by the ordered brick-and-mortar arrangement of inorganic and organic layers in nacre, we first demonstrate layered nanocomposite hydrogel (L-NC gel) films with a high clay content. The perfect micro-/nanoscale layered structure results in excellent mechanical properties higher than that of other reported NC hydrogels. We believe that it could offer innovative insights into the design of robust polymeric hydrogels for practical application.In our experiment, we prepared layered poly(N-isopropylacrylamide)-nanoclay (i.e. PNIPAM-nanoclay) hydrogel films with a nacrelike structure (Scheme 1). In a first step, clay platelets with a diameter of 28.4 nm and a thickness of 1.11 nm, the NIPAM monomer and the initiator were assembled into a lamellar structure by vacuum filtration (Scheme 1 b). [12] Then, L-NC gels were synthesized easily by in situ radical polymerization of NIPAM initiated through UV light. After polymerization, none of the hydrogel films dissolved when kept in water for a long time or sonicated, implying that PNIPAM and clay s...

Montmorillonite/poly(vinyl alcohol) (MMT/PVA) nanocomposites spanning the complete range of MMT content (0-100 wt%) are prepared by simple evaporation-induced assembly. Effects of MMT content on the structure and mechanical properties of nanocomposites are systematically investigated and exhibit two important transitions at MMT contents of 30 wt% and 70 wt%. In the range of 0-30 wt%, the nanocomposites show a random structure. With the content of PVA increasing, the mechanical properties of the resultant nanocomposites were dramatically enhanced and were higher than that by prediction according to the conventional composite model. In the range of 30-70 wt%, the nanocomposites show a nacre-like layered structure with alternating MMT platelets and PVA layers, and all PVA is completely restricted by MMT platelets. The mechanical properties of nanocomposites were further improved by increasing the content of MMT, and reached the maximum value at the MMT content of 70 wt%. The 70 wt% MMT/PVA nanocomposite has a tensile strength of 219 ± 19 MPa, which is 5.5 times higher than that of a pure PVA film and surpasses nacre and reported biomimetic layered clay/PVA composites. When the MMT content is higher than 70 wt%, the layered structure is transformed to tactoids, which deteriorate mechanical properties. These results offer comprehensive understanding for developing high-performance biomimetic layered nanocomposite materials with high nanofiller loading.