Biomaterials such as bones, teeth, and mollusk shells are known for their excellent strength, modulus, and toughness. Such properties are usually attributed to the fact that inorganic ingredients enhance the layered microstructure of nanofibers, especially two-dimensional (2D) nanosheets with a tough organic matrix. Inspired by these biological structures, synthetic strategies including layer-by-layer assembly, casting, vacuum filtration and magnetic field assist have been used to develop layered nanocomposites. How to produce super-layered nanocomposites in a universal, feasible and scalable way is still an open question.
Recently, Professor Liu Mingjie of the School of Chemistry, Beijing University of Aeronautics and Astronautics proposed a two-dimensional nanosheet arrangement induced by shear force at the incompatible hydrogel / oil interface to produce nanocomposites with highly ordered layered structures Strategy. Related papers were published on Nature on April 8, 2020, entitled "Layered nanocomposites by shear-flow induced alignment of nanosheets".
The results of the study found that the nanocomposites based on graphene oxide and clay nanosheets showed a tensile strength of up to 1215 ± 80 MPa, and the Young's modulus was 198.8 ± 6.5 GPa, which is 9.0 times and 2.8 times that of natural pearls, respectively. When using clay nanosheets, the toughness of the resulting nanocomposites can reach 36.7 ± 3.0 MJ / m2, which is 20.4 times that of natural pearls. At the same time, the tensile strength is 1195 ± 60MPa. Quantitative analysis shows that the well-arranged nanosheets form a key interface phase, which results in nanocomposites exhibiting excellent mechanical properties. At the same time, such a strategy can easily expand various two-dimensional nanofillers and be applied to the preparation of various structural composite materials, thereby promoting the development of high-performance composite materials.
Liquid flow can promote the directional assembly of nanoparticles by controlling the movement of the three-phase contact line. Recently, the authors observed that droplets can spread rapidly and completely on the gel surface in oil / water / gel systems, which is called super spreading. Studies have shown that the droplets of the reaction solution containing graphene oxide (GO) nanosheets and sodium alginate (NaAlg) can achieve ultra-fast 358 ms on the surface of polyacrylamide (PAAm) hydrogel swelled under silicone oil. Spread to form a uniform liquid layer at the hydrogel / oil interface (Figure 1a). At the same time, by using a series of extruded reaction solutions, the author extended the super-spreading process to a continuous system to produce nanocomposite films with neatly arranged nanosheets over a large area.
In this study, in a reaction solution containing well-dispersed GO nanosheets and NaAlg, by selecting an appropriate flow rate, the distance between adjacent syringes and the moving speed of the hydrogel, the solution A from the syringe will rapidly diffuse And fused to form a uniform super-diffusion solution layer at the oil / hydrogel interface. At the same time, calcium ions (Ca2 +) in the hydrogel pre-immersed in the calcium chloride solution will diffuse from the surface of the hydrogel into the super-diffusion layer of solution A and cross-link with NaAlg, which will contain GO nanoparticles within 3 minutes. The super-layup of the tablet was converted into calcium alginate (CA) hydrogel film. Subsequently, the prepared CA hydrogel film is immersed in a water bath, and can be easily separated from the hydrogel surface and dried to obtain a continuous and uniform defect-free GO / CA nanocomposite film with a width of about 5 cm.
In summary, the authors propose a generalized and scalable layering method based on super-spreading shear flow-induced nanosheet arrangement at the immiscible hydrogel / oil interface, which consists of multiple polymers And 2D nanofiller directly manufacturing layered nanocomposite membrane method, at the same time has great potential in practical applications.