A review of experimental techniques to produce a nacre-like structure

Facile and universal superhydrophobic modification to fabricate waterborne, multifunctional nacre-mimetic films with excellent stability

Although numerous kinds of waterborne, nacre-mimetic films with excellent properties have been fabricated via different assembly methods, it remains difficult to put those kinds of lightweight materials into practical applications because they are sensitive to water in the environment. Herein, a simple superhydrophobic modification method was used to enhance the repellency of film to water and/or corrosive liquids in the environment. Furthermore, it lowered the gas transmission rate of the films dramatically and improved the heat and flame shield capabilities. This approach could also be applied to other kinds of nacre-mimetic films, proving to be a versatile, low-cost, fast, and facile method to produce large-area and thick, waterborne, multifunctional films with excellent repellency to water and some corrosive liquids in the environment, which will pave the road for the practical applications of nacre-mimetic films.

Phase diagram of inverse patchy colloids assembling into an equilibrium laminar phase

We numerically study the phase behavior of colloidal particles with two charged patches at the poles and an oppositely charged equatorial belt. Interactions between particles are described using the inverse patchy colloid model, where the term inverse emphasizes the difference with respect to conventional patchy particles: as a consequence of the heterogeneous charge distribution, the patches on the particle surface repel each other, whereas the patches and non-patch regions mutually attract. For the model parameters considered in this work, the system exhibits an unusual equilibrium phase diagram characterized by a broad region where a novel structure composed of parallel colloidal monolayers is stable.

Urease-induced calcification of segmented polymer hydrogels - a step towards artificial biomineralization

Natural organic/inorganic composites, such as nacre, bones and teeth, are perfectly designed materials with exceptional mechanical properties. Numerous approaches have been taken to synthetically prepare such composites. The presented work describes a new way of mineralizing bulk materials on a large scale following the approach of bioinduced mineralization. To this end, a series of polymer conetworks with entrapped urease were prepared. After polymerization, the entrapped urease shows high enzymatic activity. The bioactive polymer conetworks were then treated with an aqueous mixture of urea and CaCl2. The urease-induced calcification indeed allows formation of carbonate crystals exclusively within the hydrogel even at room temperature. The influence of network composition, degree of cross-linking, immobilized urease concentration and temperature of calcification were investigated. By varying these parameters, spherical, monolithic clusters, as well as bar-like nanocrystals with different aspect ratios in spherical or dendritic arrays, are formed. The grown nanocrystals improve the stiffness of the starting material by up to 700-fold, provided that the microstructure shows a dense construction without pores and strong interaction between crystals and network. The process has the potential to generate a new class of hybrid materials that would be available on the macroscopic scale for use in lightweight design and medicine.

Mechanical reinforcement of epoxy with self-assembled synthetic clay in smectic order

Epoxy films containing self-assembled 2D colloidal α-zirconium phosphate nanoplatelets (ZrP) in smectic order were prepared using a simple, energy-efficient fabrication process suitable to industrial processing. The ZrP nanoplatelets form a chiral smectic mesophase with simultaneous lamellar order and helical arrangements in epoxy. The epoxy nanocomposite films are transparent and flexible and exhibit exceptionally high tensile modulus and strength. The findings have broad implications for development of multifunctional materials for engineering applications.

Unique impact behavior and toughening mechanism of the polypropylene and poly(ethylene-co-octene) alternating multilayered blends with superior toughness

In this study, the alternating multilayered PP/POE blends with different layers were successfully fabricated by micro-co-extrusion. The notable improvement of toughness in the alternating multilayered blends is ascribed to the synergetic effects of the interfaces delaminations, craze deflection, larger subcritical damage zone during the fracture process.

Mechanics of platelet-reinforced composites assembled using mechanical and magnetic stimuli

Current fabrication technologies of structural composites based on the infiltration of fiber weaves with a polymeric resin offer good control over the orientation of long reinforcing fibers but remain too cumbersome and slow to enable cost-effective manufacturing. The development of processing routes that allow for fine control of the reinforcement orientation and that are also compatible with fast polymer processing technologies remains a major challenge. In this paper, we show that bulk platelet-reinforced composites with tailored reinforcement architectures and mechanical properties can be fabricated through the directed-assembly of inorganic platelets using combined magnetic and mechanical stimuli. The mechanical performance and fracture behavior of the resulting composites under compression and bending can be deliberately tuned by assembling the platelets into designed microstructures. By combining high alignment degree and volume fractions of reinforcement up to 27 vol %, we fabricated platelet-reinforced composites that can potentially be made with cost-effective polymer processing routes while still exhibiting properties that are comparable to those of state-of-the-art glass-fiber composites.

Ionic supramolecular bonds preserve mechanical properties and enable synergetic performance at high humidity in water-borne, self-assembled nacre-mimetics

Although tremendous effort has been focused on enhancing the mechanical properties of nacre-mimetic materials, conservation of high stiffness and strength against hydration-induced decay of mechanical properties at high humidity remains a fundamental challenge in such water-borne high-performance materials. Herein, we demonstrate that ionic supramolecular bonds, introduced by infiltration of divalent Cu(2+) ions, allow efficient stabilization of the mechanical properties of self-assembled water-borne nacre-mimetics based on sustainable sodium carboxymethylcellulose (Na(+)CMC) and natural sodium montmorillonite nanoclay (Na(+)MTM) against high humidity (95% RH). The mechanical properties in the highly hydrated state (Young's modulus up to 13.5 GPa and tensile strength up to 125 MPa) are in fact comparable to a range of non-crosslinked nacre-mimetic materials in the dry state. Moreover, the Cu(2+)-treated nacre-inspired materials display synergetic mechanical properties as found in a simultaneous improvement of stiffness, strength and toughness, as compared to the pristine material. Significant inelastic deformation takes place considering the highly reinforced state. This contrasts the typical behaviour of tight, covalent crosslinks and is suggested to originate from a sacrificial, dynamic breakage and rebinding of transient supramolecular ionic bonds. Considering easy access to a large range of ionic interactions and alteration of counter-ion charge via external stimuli, we foresee responsive and adaptive mechanical properties in highly reinforced and stiff bio-inspired bulk nanocomposites and in other bio-inspired materials, e.g. nanocellulose papers and peptide-based materials.

Strong composite films with layered structures prepared by casting silk fibroin-graphene oxide hydrogels

Composite films of graphene oxide (GO) sheets and silk fibroin (SF) with layered structures have been prepared by facile solution casting of SF-GO hydrogels. The as-prepared composite film containing 15% (by weight, wt%) of SF shows a high tensile strength of 221 ± 16 MPa and a failure strain of 1.8 ± 0.4%, which partially surpass those of natural nacre. Particularly, this composite film also has a high modulus of 17.2 ± 1.9 GPa. The high mechanical properties of this composite film can be attributed to its high content of GO (85 wt%), compact layered structure and the strong hydrogen bonding interaction between SF chains and GO sheets.

Facile access to large-scale, self-assembled, nacre-inspired, high-performance materials with tunable nanoscale periodicities

Although advances have been reported to mimic the mechanically excellent structure of natural nacre, larger-scale applications are still limited due to time and energy-intensive preparation pathways. Herein, we demonstrate that simple high-shear homogenization of dispersions containing biobased high molecular weight sodium carboxymethyl cellulose (700 kg/mol, CMC) and natural sodium montmorillonite (MTM), serving as the soft energy-dissipating phase and reinforcing platelets, respectively, can be used to prepare large-area and thick films with well-aligned hard/soft nacre-mimetic mesostructure. During this process, core-shell nanoplatelets with intrinsic hard/soft structure form, which then self-assemble into a layered nanocomposite during water removal. The nanoscale periodicities of the alternating hard/soft layers can be precisely tuned by changing the ratio of CMC to MTM, which allows studying the evolution of mechanical properties as a function of the lamellar nanoscale periodicity and fractions of hard to soft material. Remarkable mechanical stiffness (25 GPa) and strength (320 MPa) can be obtained placing these materials among the top end of nacre-inspired materials reported so far. Mechanical homogenization also allows direct preparation of concentrated, yet homogeneous, gel-like dispersions of high nanoclay content, suited to doctor-blade large-area and thick films with essentially the same properties as films cast from dilute dispersions. In terms of functional properties, we report high-transparency, shape-persistent fire-blocking and the ability to surface-pattern via inkjet printing. Considering the simple, fully scalable, waterborne preparation pathway, and the use of nature-based components, we foresee applications as ecofriendly, bioinspired materials to promote sustainable engineering materials and novel types of functional barrier coatings and substrates.