Superior Performance of Artificial Nacre Based on Graphene Oxide Nanosheets

Preparation of photoluminescent nano-biocomposite nacre from graphene oxide and polylactic acid

Nano-biocomposites of inorganic and organic components wereprepared to produce long-persistent phosphorescent artificial nacre-like materials. Biodegradable polylactic acid (PLA), graphene oxide (GO), and nanoparticles (13-20 nm) of lanthanide-doped aluminate pigment (NLAP) were used in a simple production procedure of an organic/inorganic hybrid nano-biocomposite. Both polylactic acid and GO nanosheets were chemically modified to form covalent and hydrogen bonding. The high toughness, good tensile strength, and great endurance of those bonds were achieved by their interactions at the interfaces. Long-persistent and reversible photoluminescence was shown by the prepared nacre substrates. Upon excitation at 365 nm, the nacre substrates generated an emission peak at 517 nm. When ultraviolet light was shone on luminescent nacres, they displayed a bright green colour. The high superhydrophobicity of the generated nacres was obtained without altering their mechanical characteristics.

Research Progress in Preparation, Properties and Applications of Biomimetic Organic-Inorganic Composites with "Brick-and-Mortar" Structure

Inspired by nature, materials scientists have been exploring and designing various biomimetic materials. Among them, composite materials with brick-and-mortar-like structure synthesized from organic and inorganic materials (BMOIs) have attracted increasing attention from scholars. These materials have the advantages of high strength, excellent flame retardancy, and good designability, which can meet the requirements of various fields for materials and have extremely high research value. Despite the increasing interest in and applications of this type of structural material, there is still a dearth of comprehensive reviews, leaving the scientific community with a limited understanding of its properties and applications. In this paper, we review the preparation, interface interaction, and research progress of BMOIs, and propose possible future development directions for this class of materials.

Supramolecular temperature responsive assembly of polydopamine reduced graphene oxide

Graphene oxide (GO) and reduced graphene oxide (rGO) colloidal systems can directly respond to environmental stimuli such as pH, ionic strength, and light by themselves, but not to temperature. Here we show that surface modification of rGO with polydopamine (PDA) leads to a temperature-responsive composite material, even though neither rGO nor PDA have intrinsic temperature responsiveness. Reducing GO with dopamine results in rGO/PDA flakes with hydrophilic PDA clusters attached to hydrophobic rGO domains, which mimics the amphiphilic structure of temperature responsive poly(N-isopropylacrylamide) (PNIPAM). The rGO/PDA flakes self-assemble at temperature higher than 30 °C, causing flake aggregation and precipitation in suspensions with concentration of 0.05 g L^-1, which is reversible upon cooling, shaking, and re-heating. A solution-to-gelation transition occurs upon heating suspensions with concentration of 10 g L^-1. Nacre-like films and porous monoliths are obtained by drying rGO/PDA suspensions at different concentrations. Films and porous monoliths obtained by drying suspensions that are previously self-assembled through heat have more compact structures compared to those obtained with suspensions that are not heated. Overall, this work introduces the concept of supramolecular temperature responsive assembly of nanomaterials (STRAN), i.e., that temperature response can be introduced in nanomaterials by combining non-responsive components that function cooperatively in supramolecules, whose interactions with solvents can be modulated by temperature changes, mimicking what happens in macromolecular systems such as PNIPAM. STRAN could be applied to nanomaterials beyond GO to develop responsive systems whose self-assembly in suspension and architectural features realized upon drying can be controlled by temperature.

Review of Artificial Nacre for Oil–Water Separation

Due to their extraordinary prospective uses, particularly in the areas of oil–water separation, underwater superoleophobic materials have gained increasing attention. Thus, artificial nacre has become an attractive candidate for oil–water separation due to its superhydrophilicity and underwater superoleophobicity properties. Synthesized artificial nacre has successfully achieved a high mechanical strength that is close to or even surpasses the mechanical strength of natural nacre. This can be attributed to suitable synthesis methods, the selection of inorganic fillers and polymer matrices, and the enhancement of the mechanical properties through cross-linking, covalent group modification, or mineralization. The utilization of nacre-inspired composite membranes for emerging applications, i.e., is oily wastewater treatment, is highlighted in this review. The membranes show that full separation of oil and water can be achieved, which enables their applications in seawater environments. The self-cleaning mechanism’s basic functioning and antifouling tips are also concluded in this review.

Quaternary Artificial Nacre-Based Electronic Textiles with Enhanced Mechanical and Flame-Retardant Performance

Interest in wearable electronics has led to extensive studies on woven textiles that are mechanically robust and stretchable, have high electrical conductivities, and exhibit fire resistance properties even at high temperatures. We demonstrate a highly easy and scalable method for fabricating defect-free graphene (dfG) nacre-based woven electronic textiles (e-textiles) with enhanced flame-retardant properties and high electronic conductivities. The as-prepared graphene shows perfect preservation of its inherent properties without any crystal damage during subsequent exfoliation and noncovalent melamine functionalization. The defect-free graphene functionalized by melamine (m-dfG) is well dispersed in various polar solvents. To investigate the synergistic effect of m-dfG, quaternary artificial nacre composites are fabricated by adding manganese(II) chloride to a m-dfG/polymer (carboxymethyl cellulose (CMC)) composite. Their mechanical, electrical, and thermal characteristics are then evaluated. The quaternary m-dfG-Mn²⁺-CMC artificial nacre exhibits exceptionally enhanced mechanical properties (tensile strength: 613.9 MPa; toughness: 7.13 MJ m^-3) and the best flame retardancy (even at torch heating) as compared to those of graphene oxide/reduced graphene oxide (GO/rGO)-based nacres. In this context, our approach will be helpful to future wearable electronics and fire-retardant textiles with high strength, which can accelerate the commercial viability of e-textiles.

Insights on Shear Transfer Efficiency in "Brick-and-Mortar" Composites Made of 2D Carbon Nanoparticles

Achieving high mechanical performances in nanocomposites reinforced with lamellar fillers has been a great challenge in the last decade. Many efforts have been made to fabricate synthetic materials whose properties resemble those of the reinforcement. To achieve this, special architectures have been considered mimicking existing materials, such as nacre. However, achieving the desired performances is challenging since the mechanical response of the material is influenced by many factors, such as the filler content, the matrix molecular mobility and the compatibility between the two phases. Most importantly, the properties of a macroscopic bulk material strongly depend on the interaction at atomic levels and on their synergetic effect. In particular, the formation of highly-ordered brick-and-mortar structures depends on the interaction forces between the two phases. Consequently, poor mechanical performances of the material are associated with interface issues and low stress transfer from the matrix to the nanoparticles. Therefore, improvement of the interface at the chemical level enhances the mechanical response of the material. The purpose of this review is to give insight into the stress transfer mechanism in high filler content composites reinforced with 2D carbon nanoparticles and to describe the parameters that influence the efficiency of stress transfer and the strategies to improve it.

Pistachio-Inspired Bulk Graphene Oxide-Based Materials with Shapeability and Recyclability

Nowadays, despite the fact that recent progress has been reported to mimic natural structural materials (especially nacre), designing bioinspired ultrastrong composites in a universal, viable, and scalable manner still remains a long-standing challenge. In particular, pistachio shells show high tissue strength attributed to the cellulose sheet laminated microstructures. Compared with nacre, pistachio shells own interlocking mortise-tenon joints in their structure, which offer higher energy dissipation and deformability. Here we present a strategy to produce nanocomposites with pistachio-mimetic structures through repeated kneading of graphene oxide (GO) in a dynamic covalent and supramolecular poly(sodium thioctic) (pST) system. The dynamic nature of the polymeric backbones endows the resultant GO-based composite with full recyclability and three-dimensional shapeability. The superior mechanical properties of the pistachio-mimetic composite can be attributed to the mortise-tenon joints design in the structure, which has not been achieved in the nacre-mimetic composite. The resulting composite also exhibits high thermal conductivity (15.6 W/(m·K)), yielding an alternative approach to design in engineered and thermal management materials.

Wood-Derived Composites with High Performance for Thermal Management Applications

Fabricating advanced polymer composites with remarkable mechanical and thermal conductivity performances is desirable for developing advanced devices and equipment. In this study, a novel strategy to prepare anisotropic wood-based scaffolds with a naturally aligned microchannel structure from balsa wood is demonstrated. The wood microchannels were coated with polydopamine-surface-modified small graphene oxide (PGO) nanosheets via assembly. The highly aligned porous microstructures, with thin wood cell walls and large voids along the cellulose microchannels, allow polymers to enter, resulting in the fabrication of the wood-polymer nanocomposite. The tensile stiffness and strength of the resulting nanocomposite reach 8.10 GPa and 90.3 MPa with a toughness of 5.0 MJ m^-3. The thermal conductivity of the nanocomposite is improved significantly by coating a PGO layer onto the wood scaffolds. The nanocomposite exhibits not only ultrahigh thermal conductivity (in-plane about 5.5 W m^-1 K^-1 and through-plane about 2.1 W m^-1 K^-1) but also satisfactory electrical insulation (volume resistivity of about 10¹⁵ Ω·cm). Therefore, the results provide a strategy to fabricate thermal management materials with excellent mechanical properties.

Flexible core-shell Cs x WO3-based films with high UV/NIR filtration efficiency and stability

Cesium-doped tungsten bronze Cs _x WO₃ (CWO) is an ideal near infrared (NIR) shielding material for solar filters. However, the NIR shielding ability of CWO-dispersed films easily deteriorates in hot humid environments, which severely hinders the commercial application of CWO. In this paper, UV/NIR shielding nanocomposite films were prepared by dispersing core-shell structured CWO@polydopamine (CWO@PDA) in a poly(vinyl alcohol) matrix. Because of the strong ultraviolet light absorption ability of PDA, it can shield ultraviolet light, which is generally detrimental to our health. The prepared nanocomposite films can efficiently shield 88.3% UV and 85.5% NIR radiation even though they show relatively high transparency in the visible range. Importantly, the good protection of the continuous PDA shells played an important role in enhancing the stability of CWO nanoparticles. The nanocomposite films also exhibit excellent stability in hot humid environments. Therefore, core-shell structured CWO@PDA nanoparticles have great potential as a novel UV/NIR shielding material for the development of efficient energy-saving windows.

Structure-Function Relationships of Nanocarbon/Polymer Composites for Chemiresistive Sensing: A Review

Composites of organic compounds and inorganic nanomaterials provide novel sensing platforms for high-performance sensor applications. The combination of the attractive functionalities of nanomaterials with polymers as an organic matrix offers promising materials with tunable electrical, mechanical, and chemisensitive properties. This review mainly focuses on nanocarbon/polymer composites as chemiresistors. We first describe the structure and properties of carbon nanofillers as reinforcement agents used in the manufacture of polymer composites and the sensing mechanism of developed nanocomposites as chemiresistors. Then, the design and synthesizing methods of polymer composites based on carbon nanofillers are discussed. The electrical conductivity, mechanical properties, and the applications of different nanocarbon/polymer composites for the detection of different analytes are reviewed. Lastly, challenges and the future vision for applications of such nanocomposites are described.

Bioproduced Polymers Self-Assemble with Graphene Oxide into Nanocomposite Films with Enhanced Mechanical Performance

Graphene oxide (GO) has recently been highlighted as a promising multipurpose two-dimensional material. However, free-standing graphene oxide films suffer from poor strength and flexibility, which limits scaling-up of production and lifetime structural robustness in applications. Inspired by the relationship between the organic and inorganic components of the hierarchical structure of nacre found in mollusk shells, we have fabricated self-assembled, layered graphene-based composite films. The organic phase of our composite is produced via environmentally friendly and economical methods based on bacterial production of γ-poly(glutamic acid) (PGA). Composite films made of GO, PGA, and divalent cations (Ca²⁺) were prepared through a slow solvent evaporation method at ambient temperature, resulting in a nacre-like layered structure. These biobased nanocomposite films showed impressive mechanical properties, which resulted from a synergistic combination of hydrogen bonding with the bacterially produced PGA and ionic bonding with calcium ions (Ca²⁺). The GO/PGA/Ca²⁺ composite films possessed a high strength of 150 ± 51.9 MPa and a high Young's modulus of 21.4 ± 8.7 GPa, which represents an increase of 120% and over 70% with respect to pure GO films. We provide rational design strategies for the production of graphene-based films with improved mechanical performance, which can be applied in filtration purification of wastewater in the paper, food, beverage, pigment, and pharmaceuticals industries, as well as for manufacturing of functional membranes and surface coatings.

Artificial Nacre Epoxy Nanomaterials Based on Janus Graphene Oxide for Thermal Management Applications

Owing to the development of microelectronics, demands for excellent thermal dissipation materials have substantially increased. Learning from natural nacre, thermally conductive epoxy nanocomposites were prepared based on asymmetrically polydopamine-functionalized Janus graphene oxide (JPGO) scaffolds. The required highly oriented JPGO scaffolds were prepared via the bidirectional freeze-casting method. With the addition of epoxy resin, the resulting nanocomposite reveals anisotropic thermal properties. With the total content of the JPGO scaffold being 0.93 wt %, almost 35 times enhancement of in-plane thermal conductivity (perpendicular to the lamellar structure) (∼5.6 W m^-1 K^-1) has been obtained. The single-side-functionalized JPGO scaffolds play an important role in forming thermal conductive networks for the epoxy nanocomposites. Importantly, the nanocomposites present electrically insulating properties (>10¹⁴ Ω cm). Such high-performance nanocomposites have promising applications for thermal management in electronic devices.

Carbonization of Polydopamine-Coating Layers on Boron Nitride for Thermal Conductivity Enhancement in Hybrid Polyvinyl Alcohol (PVA) Composites

Inspired by mussel adhesion proteins, boron nitride (BN) particles coated with homogeneous polydopamine (BNPDA) were prepared, and through an annealing process, a carbonized PDA layer on the surface of BN was obtained, which exhibited a nanocrystalline graphite-like structure. The effect of carbonization of PDA coating layer on BN particles was characterized by various analytical techniques including SEM, TEM, Raman spectroscopy, and XPS. When the resulting particles were used as a thermally conductive filler for polyvinyl alcohol (PVA) composite films, enhanced thermal conductivity was observed compared to raw BN composite due to the ordered structure and improved solubility in water. Furthermore, the homogeneous dispersion of the filler and excellent flexibility of the modified composite film with 21 wt % filler may be attributed to compatibility with the PVA chain. As the whole fabrication process did not use toxic chemicals (mainly water was used as the solvent), it may contribute to green and sustainable chemistry.

Synergistic effects in Methylcellulose/Hydroxyethylcellulose blend: Influence of components ratio and graphene oxide

A specific feature of water-soluble polysaccharides is formation of organized structures in solutions. This study deals with an unexpected effect of 2-hydroxyethylcellulose (HEC) on structure and mechanical performance of methylcellulose (MC) films. The values of modulus with 5 and 10 % HEC content exceed those of the linear model, which indicates synergistic effect consisting in formation of ordered structures. However, higher content of HEC leads to worse properties corresponding to contribution of its lower parameters. The structural transformations are confirmed by XRD and polarized-light microscopy. Ability of HEC to support formation of ordered structures in MC solutions is indicated by rheology. Important fact is that low graphene oxide (GO) content has a high reinforcing effect on neat MC or HEC, but its presence in blends is accompanied by elimination of HEC-induced structural transformations. The results confirm complex effect of blending and GO on structure and properties of the MC/HEC system.

Photothermal-Responsive Graphene Oxide Membrane with Smart Gates for Water Purification

In this work, photothermal-responsive graphene oxide (GO)-based membranes intercalated by multiwalled carbon nanotubes (MWCNTs) were prepared by polydopamine (PDA) modification and 2-ureido-4[1H]-pyrimidinone (UPy) assembly process. Benefited from the high photothermal conversion ability of PDA and reversible UPy dimer, the permeation flux of the GO-based membrane can be easily modulated with a high gating ratio under near-infrared light switched off and on. Nanochannels created by the intercalation of MWCNTs into GO layers greatly increase water permeation without sacrificing the rejection of dye molecules in water (96.2% for methyl orange, 98.9% for rhodamine B, and 99.7% for Coomassie brilliant blue). The composite membranes also exhibit trade-off between rejection of heavy metal ions (Cu²⁺ and Fe³⁺). Moreover, such GO-based membranes show high pH stabilities, which show great potential in the water purification applications.

Fabrication of thermally conductive and electrically insulating polymer composites with isotropic thermal conductivity by constructing a three-dimensional interconnected network

Efficient heat removal via thermal management materials has become one of the most critical challenges in the development of modern microelectronic devices. However, the conventional polymer-based thermally conductive composites with randomly distributed filler particles usually yield an undesired value because of the lack of efficient heat transfer pathways. Therefore, constructing a three-dimensional interconnected filler structure is greatly desirable for realizing high thermal conductivity enhancement in composites. Herein, graphene oxide (GO) was used as a thermally conductive filler due to its excellent thermal conductivity and coated with polydopamine (PDA) to enhance its electric insulation performance. A unique "particle-constructing" method was adopted for fabricating highly ordered three-dimensional GO-based polymer composites, throughout which the GO-PDA formed an intact, uniform and well-defined network structure. The composite, even with a very low GO-PDA loading of 0.96 vol%, exhibited both high in-plane (4.13 W m^-1 K^-1) and through-plane (4.56 W m^-1 K^-1) thermal conductivities and also presented excellent electrically insulating properties (>10¹⁴Ω cm). These composites have promising applications in heat dissipation of next-generation portable and collapsible electronic devices.

Polymer nanocomposites having a high filler content: synthesis, structures, properties, and applications

The recent development of nanoscale fillers, such as carbon nanotubes, graphene, and nanocellulose, allows the functionality of polymer nanocomposites to be controlled and enhanced. However, conventional synthesis methods of polymer nanocomposites cannot maximise the reinforcement of these nanofillers at high filler content. Approaches for the synthesis of high content filler polymer nanocomposites are suggested to facilitate future applications. The fabrication methods address the design of the polymer nanocomposite architecture, which encompasses one, two, and three dimensional morphologies. Factors that hamper the reinforcement of nanostructures, such as alignment, dispersion of the filler and interfacial bonding between the filler and polymer, are outlined. Using suitable approaches, maximum potential reinforcement of nanoscale fillers can be anticipated without limitations in orientation, dispersion, and the integrity of the filler particle-matrix interface. High filler content polymer composites containing emerging materials such as 2D transition metal carbides, nitrides, and carbonitrides (MXenes) are expected in the future.

Strong, Conductive, Foldable Graphene Sheets by Sequential Ionic and π Bridging

The goal of this work is to develop an inexpensive low-temperature process that provides polymer-free, high-strength, high-toughness, electrically conducting sheets of reduced graphene oxide (rGO). To develop this process, we have evaluated the mechanical and electrical properties resulting from the application of an ionic bonding agent (Cr3+ ), a π-π bonding agent comprising pyrene end groups, and their combinations for enhancing the performance of rGO sheets. When only one bonding agent was used, the π-π bonding agent is much more effective than the ionic bonding agent for improving both the mechanical and electrical properties of rGO sheets. However, the successive application of ionic bonding and π-π bonding agents maximizes tensile strength, toughness, long-term electrical stability in various corrosive solutions, and resistance to mechanical abuse and ultrasonic dissolution. Using a combination of ionic bonding and π-π bonding agents, high tensile strength (821 MPa), high toughness (20 MJ m-3 ), and electrical conductivity (416 S cm-1 ) were obtained, as well as remarkable retention of mechanical and electrical properties during ultrasonication and mechanical cycling by both sheet stretch and sheet folding, suggesting high potential for applications in aerospace and flexible electronics.

Artificial Nacre from Supramolecular Assembly of Graphene Oxide

Inspired by the "brick-and-mortar" structure and remarkable mechanical performance of nacre, many efforts have been devoted to fabricating nacre-mimicking materials. Herein, a class of graphene oxide (GO) based artificial nacre material with quadruple hydrogen-bonding interactions was fabricated by functionalization of polydopamine-capped graphene oxide (PDG) with 2-ureido-4[1 H]-pyrimidinone (UPy) self-complementary quadruple hydrogen-bonding units followed by supramolecular assembly process. The artificial nacre displays a strict "brick-and-mortar" structure, with PDG nanosheets as the brick and UPy units as the mortar. The resultant nanocomposite shows an excellent balance of strength and toughness. Because of the strong strengthening via quadruple hydrogen bonding, the tensile strength and toughness can reach 325.6 ± 17.8 MPa and 11.1 ± 1.3 MJ m^-3, respectively, thus exceeding natural nacre, and reaching 3.6 and 10 times that of a pure GO artificial nacre. Furthermore, after further H₂O treatment, the resulting H₂O-treated PDG-UPy actuator displays significant bending actuations when driven by heat. This work provides a pathway for the development of artificial nacre for their potential applications in energy conversion, temperature sensor, and thermo-driven actuator.

Effects of Melanin on Optical Behavior of Polymer: From Natural Pigment to Materials Applications

Melanin is a kind of ubiquitous natural pigment, which serves a variety of protective functions in many organisms. In the present study, natural melanin and synthetic melanin nanoparticles (NPs) were systematically investigated for its potential application in polymeric optical materials. A significant short-wavelength shielding and high visible light transparency polymer nanocomposite was easily obtained via tuning the melanin particle size. In particular, the nanocomposite film with melanin NPs (diameter ≈ 15 nm) loading even as low as 1 wt % blocks most ultraviolet light below 340 nm and still keeps high visible light transparency (83%) in the visible spectrum. More importantly, because of the excellent photoprotection and radical scavenging capabilities of melanin, the resulting polymer nanocomposite exhibits outstanding photostability. In effect, such fantastic melanin NPs is promising for applications in various optical materials.

Graphene-assisted fabrication of poly(ε-caprolactone)-based nanocomposites with high mechanical properties and self-healing functionality

A fast NIR light-induced self-healing PCL nanocomposite with superior mechanical properties was achieved by tailoring the cyclic mechanical annealing process.

A Novel UV-Shielding and Transparent Polymer Film: When Bioinspired Dopamine-Melanin Hollow Nanoparticles Join Polymers

Ultraviolet (UV) light is known to be harmful to human health and cause organic materials to undergo photodegradation. In this Research Article, bioinspired dopamine-melanin solid nanoparticles (Dpa-s NPs) and hollow nanoparticles (Dpa-h NPs) as UV-absorbers were introduced to enhance the UV-shielding performance of polymer. First, Dpa-s NPs were synthesized through autoxidation of dopamine in alkaline aqueous solution. Dpa-h NPs were prepared by the spontaneous oxidative polymerization of dopamine solution onto polystyrene (PS) nanospheres template, followed by removal of the template. Poly(vinyl alcohol) (PVA)/Dpa nanocomposite films were subsequently fabricated by a simple casting solvent. UV irradiation protocols were set up, allowing selective study of the extra-shielding effects of Dpa-s versus Dpa-h NPs. In contrast to PVA/Dpa-s films, PVA/Dpa-h films exhibit stronger UV-shielding capabilities and can almost block the complete UV region (200-400 nm). The excellent UV-shielding performance of the PVA/Dpa-h films mainly arises from multiple absorption because of the hollow structure and large specific area of Dpa-h NPs. Moreover, the wall thickness of Dpa-h NPs can be simply controlled from 28 to 8 nm, depending on the ratio between PS and dopamine. The resulting films with Dpa-h NPs (wall thickness = ∼8 nm) maintained relatively high transparency to visible light because of the thinner wall thickness. The results indicate that the prepared Dpa-h NPs can be used as a novel UV absorber for next-generation transparent UV-shielding materials.

High rate performance SnO2based three-dimensional graphene composite electrode for lithium-ion battery applications

A composite of SnO₂and three-dimensional graphene (SnO₂/3DG) was fabricated using a hydrothermal method, with polystyrene balls (PS) as templates, and was found to have excellent electrochemical performance..