Multifunctional Structural Materials Research Articles

Growing recyclable and healable piezoelectric composites in 3D printed bioinspired structure for protective wearable sensor

Bionic multifunctional structural materials that are lightweight, strong, and perceptible have shown great promise in sports, medicine, and aerospace applications. However, smart monitoring devices with integrated mechanical protection and piezoelectric induction are limited. Herein, we report a strategy to grow the recyclable and healable piezoelectric Rochelle salt crystals in 3D-printed cuttlebone-inspired structures to form a new composite for reinforcement smart monitoring devices. In addition to its remarkable mechanical and piezoelectric performance, the growth mechanisms, the recyclability, the sensitivity, and repairability of the 3D-printed Rochelle salt cuttlebone composite were studied. Furthermore, the versatility of composite has been explored and applied as smart sensor armor for football players and fall alarm knee pads, focusing on incorporated mechanical reinforcement and electrical self-sensing capabilities with data collection of the magnitude and distribution of impact forces, which offers new ideas for the design of next-generation smart monitoring electronics in sports, military, aerospace, and biomedical engineering.

Improved mechanical-physical performances of copper composites with reduced graphene oxide and carbonized polymer dots as multi-scale synergetic reinforcements

The development of high-performance (structure-function integration) Cu matrix composites have become a focus by introducing the novel hybrid carbon nanomaterials and giving full play to the synergistic effect. It is a great challenge to homogeneously disperse the ex-situ nano-filler within matrix for excellent performances. In this study, the two-dimensional reduced graphene oxide (RGO) and zero-dimensional carbonized polymer dots (CPD) were incorporated with Cu-based powders by the molecular level mixing (MLM) and high-energy ball milling (HBM) methods, respectively. Results revealed that RGO (MLM)/CPD (HBM)-Cu bulk composites sintered at 650 °C displayed higher ultimate tensile strength (367 MPa) and better failure strain (∼30%) as compared with pure Cu (MLM/HBM). Meanwhile, the electrical conductivity of RGO (MLM)/CPD (HBM)-Cu was almost equal to that of pure Cu (93.74% IACS), exhibiting a promising prospect in applications as advanced multifunctional structural materials. It was well proved that the interface strength of RGO-Cu and the dispersibility of hybrid reinforcements were improved by the incorporation of CPD, which further enhanced the synergistic effects of (CPD + RGO) and achieved better mechanical-physical performances.

Microstructure and properties of FeCoNiCrAl high-entropy alloy particle-reinforced Cu-matrix composites prepared via FSP

Although copper has excellent thermal conductivity, poor wear resistance seriously limits its development. In this paper, a Cu matrix surface composite material reinforced by FeCoNiCrAl high-entropy alloy particles was prepared by friction stir processing. The microstructure and properties of the composite were investigated. The results showed that both the FSP process and the addition of HEA particles contributed to the refinement of the Cu-matrix grains. A diffusion layer with a width of about 0.8 µm was formed at the interface between the HEA particles and the Cu matrix. Compared with received Cu, the microhardness of Cu matrix in the composites was increased by 69.8%, the wear rate was reduced by 29.7%, and the wear resistance was significantly improved. Mean while, the ductility of the composite was consistent with that of the received Cu, and the thermal conductivity reached 87% of the received Cu. Therefore, this paper provided a new possibility for developing multifunctional structural materials with high wear resistance, high ductility, and high thermal conductivity.

Dynamic behavior of structural beams made of innovative smart concrete

The monitoring of structures and infrastructures is nowadays a pivotal activity for guaranteeing the safety of their users. Environmental conditions and exceptional events could affect their performance and integrity, shorten their service lives and even produce unexpected failures. The development of multifunctional smart structural materials with enhanced or novel properties could help to prevent or reduce damages and collapses. Among other building materials, concrete is particularly suitable for such improvements due to its composite nature. The authors have developed a smart concrete doped with carbon microfibers capable to sense variations of applied strains/stresses. The investigation started from the analysis of the performances of small samples, up to the manufacture of two full-scale RC beams. These applications at realistic scales are crucial for a diffuse use of such smart materials in civil engineering. The paper describes the novel characteristics of full-scale smart concrete beams, investigating their main physical, electrical, and monitoring capabilities. For this purpose, dynamic tests are carried out and discussed.

Polymerization and Applications of Poly(methyl methacrylate)-Graphene Oxide Nanocomposites: A Review.

Graphene oxide (GO)-incorporated poly(methyl methacrylate) (PMMA) nanocomposites (PMMA-GO) have demonstrated a wide range of outstanding mechanical, electrical, and physical characteristics. It is of interest to review the synthesis of PMMA-GO nanocomposites and their applications as multifunctional structural materials. The attention of this review is to focus on the radical polymerization techniques, mainly bulk and emulsion polymerization, to prepare PMMA-GO polymeric nanocomposite materials. This review also discusses the effect of solvent polarity on the polymerization process and the types of surfactants (anionic, cationic, nonionic) and initiator used in the polymerization. PMMA-GO nanocomposite synthesis using radical polymerization-based techniques is an active topic of study with several prospects for considerable future improvement and a variety of possible emerging applications. The concentration and dispersity of GO used in the polymerization play critical roles to ensure the functionality and performance of the PMMA-GO nanocomposites.

Importance of radial line and circulus distributions to the protectoflexibility of scales in fish armors

Fish scales are dermal armors with an attractive combination of resistance to puncture and flexibility. Past work has attributed this unique quality to their composition and the hierarchical stratification of their microstructure. Here, we show that the ridge lines and circuli of scales contribute to the overall damage tolerance and play a key role in the “protectoflexibility” of fish scales. Through application of optical mechanics, we show that the ridge lines channel damage along paths that reduce the effective stress intensity available for bulk fracture of the scales. Furthermore, comparison of the ridge line distribution and circuli in elasmodine scales shows that they are unique across fish species and appear to be tuned for the combined functional requirements, i.e., resistance to threats and locomotion. The importance of these features in the multifunctional requirements of scales is elucidated in detail, including their role in inspiring new approaches for advancing multifunctional structural materials.

Multifunctional Carbon Fiber Composites: A Structural, Energy Harvesting, Strain-Sensing Material.

Multifunctional structural materials are capable of reducing system level mass and increasing efficiency in load-carrying structures. Materials that are capable of harvesting energy from the surrounding environment are advantageous for autonomous electrically powered systems. However, most energy harvesting materials are non-structural and add parasitic mass, reducing structural efficiency. Here, we show a structural energy harvesting composite material consisting of two carbon fiber (CF) layers embedded in a structural battery electrolyte (SBE) with a longitudinal modulus of 100 GPa—almost on par with commercial CF pre-pregs. Energy is harvested through mechanical deformations using the piezo-electrochemical transducer (PECT) effect in lithiated CFs. The PECT effect creates a voltage difference between the two CF layers, driving a current when deformed. A specific power output of 18 nW/g is achieved. The PECT effect in the lithiated CFs is observed in tension and compression and can be used for strain sensing, enabling structural health monitoring with low added mass. The same material has previously been shown capable of shape morphing. The two additional functionalities presented here result in a material capable of four functions, further demonstrating the diverse possibilities for CF/SBE composites in multifunctional applications in the future.

3D Printed Electrochromic Supercapacitors with Ultrahigh Mechanical Strength and Energy Density.

With the accelerating update of advanced electronic gadgets, a great deal of attention is being paid today to the function integration and intelligent design of electronic devices. Herein, a novel kind of multitasking 3D oxygen-deficient WO3- x ∙ 2H2 O/Ag/ceramic microscaffolds, possessing simultaneous giant energy density, ultrahigh mechanical strength, and reversible electrochromic performance is proposed, and fabricated by a 3D printing technique. The ceramic microscaffolds ensure outstanding mechanical strength and stability, the topology optimized porous lattice structure provides developed surface area for coloration as well as abundant easily accessible channels for rapid ion transportation, and the bifunctional oxygen-defective pseudomaterials enable the large areal capacity and impressive electrochromic performance. As a result, this 3D-printed multitasking microscaffolds simultaneously perform structure-designable, electrochromic, compression resistant, and energy storage functions, behaving with true 3D structure with tailorable curvatures, excellent compressive strength (61.9 MPa), large color variations (>145% in b* value), good aesthetic visual quality as well as exciting electrochemical performances for energy storage including ultrahigh areal capacitance (10.05 F cm-2 at 5 mA cm-2 ), record-high energy density (0.60 mWh cm-2 ), and superior long-term cycling stability (88.6% capacity retention after 10 000 cycles). This work opens up the possibility for high-performance multi-functional coupling structural materials and integrated systems.

Hybrid Carbon Microfibers-Graphite Fillers for Piezoresistive Cementitious Composites.

Multifunctional structural materials are very promising in the field of engineering. Particularly, their strain sensing ability draws much attention for structural health monitoring applications. Generally, strain sensing materials are produced by adding a certain amount of conductive fillers, around the so-called “percolation threshold”, to the cement or composite matrix. Recently, graphite has been found to be a suitable filler for strain sensing. However, graphite requires high amounts of doping to reach percolation threshold. In order to decrease the amount of inclusions, this paper proposes cementitious materials doped with new hybrid carbon inclusions, i.e., graphite and carbon microfibers. Carbon microfibers having higher aspect ratio than graphite accelerate the percolation threshold of the graphite particles without incurring into dispersion issues. The resistivity and strain sensitivity of different fibers’ compositions are investigated. The electromechanical tests reveal that, when combined, carbon microfibers and graphite hybrid fillers reach to percolation faster and exhibit higher gauge factors and enhanced linearity.

An investigation into the performance of structural composite capacitor by Taguchi method

Structural capacitors are multifunctional structural materials that provide structural strength and energy storage together and aim to reduce greatly the weight of a system. In this paper, the effect of dielectric separator materials such as poly(vinyl chloride) (PVC) and biaxially oriented polypropylene, the weave structure of carbon (C) fabric and the thickness of dielectric material on the multifunctional performance of structural capacitors was investigated. In order to plan experiments, analyze and interpret results and optimize factors (dielectric separator material, carbon fabric weave type, dielectric material thickness) that affect the multifunctional performance, design of experiments (DOE) was used. DOE was carried out using the Taguchi method. Structural capacitor materials were manufactured according to an experimental layout based on Taguchi’s L6 orthogonal array and were mechanically and electrically tested to evaluate their multifunctional efficiency. In addition, optimal combinations of factor levels were determined, and the optimum performance that can be obtained with these combinations was calculated by applying the Taguchi method. The results show that higher electrical and mechanical performance is obtained in the structural capacitor using twill-woven fabric. Also, in particular, PVC film, which is a widely available and low-cost polymer film, can be used as dielectric material in structural capacitors.

Fracture behavior of metakaolin‐based geopolymer reinforced with carbon nanofibers

AbstractWe investigate the fracture response of metakaolin‐based geopolymer reinforced with 0.1 wt%, 0.2 wt%, and 0.5 wt% carbon nanofibers. We measure the elastoplastic response using microindentation tests. We note an increase in indentation modulus of 5%, 13%, and 21%, and an increase in indentation hardness of 9%, 18%, and 25%, respectively. We measure the fracture energy using cutting‐edge microscopic fracture tests. In our tests, a sphero‐conical diamond indenter pushes across the specimen's surface under a prescribed vertical force. We analyze the recorded penetration depth and horizontal force using nonlinear fracture mechanics and extract the fracture parameters. We find that carbon nanofibers enhance fracture resistance. The fracture toughness increases by, respectively, 38%, 40%, and 45%; meanwhile, the fracture energy increases by, respectively, 83%, 72%, and 74%. We find that carbon nanofibers lead to a densification of the microstructure. Moreover, we observe crack‐bridging mechanisms in geopolymer nanocomposites. This study is important to pave the way for novel enhanced‐performance and multifunctional structural materials.

Structural and Ecofriendly Holocellulose Materials from Wood: Microscale Fibers and Nanoscale Fibrils

Mildly delignified wood holocellulose fibers show well-preserved cellulose nanofibril (CNF) structure in the fiber cell wall. Fibers, paper, biocomposites, and compression-molded fiber materials demonstrate excellent mechanical properties. Here, wood holocellulose fibers and corresponding CNFs are discussed with respect to nanostructure, mechanical performance, and advanced materials potential. Functionalization routes are discussed, as well as materials selection, nanoscience of recycling, and the embodied energy in cellulosic candidates for multifunctional structural materials.

Retarding Ostwald Ripening to Directly Cast 3D Porous Graphene Oxide Bulks at Open Ambient Conditions.

Graphene aerogels (GAs) with attractive properties have shown tremendous potentials in energy- and environment-related applications. Unfortunately, current assembly methods for GAs such as sol-gel and freeze-casting processes must be conducted in enclosed spaces with unconventional conditions, thus being literally inoperative for in situ and continuous productions. Herein, a direct slurry-casting method at open ambient conditions is established to arbitrarily prepare three-dimensional (3D) porous graphene oxide (GO) bulks without macroscopic dimension limits on a wide range of solid surfaces by retarding Ostwald ripening of 3D liquid GO foams when being dried in air. A subsequent fast thermal reduction (FTR) of GO foams leads to the formation of graphene aerogels (denoted as FTR-GAs) with hierarchical closed-cellular graphene structures. The FTR-GAs show outstanding high-temperature thermal insulation (70% decrease for 400 °C), as well as superelasticity (>1000 compression-recovery cycles at 50% strain), ultralow density (10-28 mg cm-3), large specific surface area (BET, 206.8 m2 g-1), and high conductivity (ca. 100 S m-1). This work provides a viable method to achieve in situ preparations of high-performance GAs as multifunctional structural materials in aircrafts, high-speed trains, or even buildings for the targets of energy efficiency, comfort, and safety.

Delignification and Ionic Liquid Treatment of Wood toward Multifunctional High-Performance Structural Materials.

Wood-based multifunctional materials with excellent mechanical performance are increasingly considered for sustainable advanced applications due to their unique hierarchical structure and inherent reinforcing cellulose phase orientation. Nonetheless, a wider multipurpose utilization of wood materials is so far hampered because of constraints arising from scalable functionalization, efficient processing, facile shaping as well asnatural heterogeneity and durability. This study introduces a multifunctional all-wood material fabrication method relying on delignification, ionic liquid (IL) treatment, and pressure-assisted consolidation of wood. Structure-retaining controlled delignification of wood was performed to enable direct access to the hierarchical cellulose assembly, while preserving the highly aligned and thus beneficial wood structural directionality. As a following step, the obtained biobased scaffold with an increased porosity was infiltrated with an IL and heat-activated to partially dissolve and soften the cellulose fiber surface. Samples washed with water to remove IL exhibited pronounced isotropic flexibility, which upon combined compression and lateral shear allowed the fabrication of various 3D shapes with adjustable fiber architecture. The obtained very compact and totally additive-free all-wood materials were extensively characterized, revealing superior mechanical performance, and gained multifunctionality compared to native wood.

Synergistic strengthening effect of in-situ synthesized WC1-x nanoparticles and graphene nanosheets in copper matrix composites

In metal matrix composites, it is commonly a hard task to achieve synergistic strengthening and toughening effects between two-dimensional graphene and zero-dimensional nanoparticles (NPs) reinforcements due to their huge dimensional gap. Herein, we developed an in-situ solid-state reaction method to incorporate graphene nanosheets (GNSs) and WC1-x NPs into copper matrix. It was proved for the first time by thermodynamics and crystallography calculations that the unusual γ-WC1-x phase can be generated from the solid reaction and maintain stable at room temperature. Thanks to the unique distribution types of WC1-x, i.e. intergranular or intragranular distribution while other parts anchored on the surface of the GNSs, Orowan strengthening and load transfer strengthening were simultaneously achieved in the composites. Meanwhile, the thermal conductivity was also measured to be equal to that of pure Cu, exhibiting a promising prospect in applications as advanced multifunctional structural materials.

Optimized microstructures for multifunctional structural electrolytes

Multifunctional structural materials offer compelling opportunities to realize highly efficient products. However, the need to fulfil disparate functions generates intrinsically conflicting physical property demands. One attractive strategy is to form a bi-continuous architecture of two disparate phases, each addressing a distinct physical property. For example, structural polymer electrolytes combine rigid and ion-conducting phases to deliver the required mechanical and electrochemical performance. Here, we present a general methodology, based on topology optimization, to identify optimal microstructures for particular design considerations. The numerical predictions have been successfully validated by experiments using 3D printed specimens. These architectures are directly relevant to multifunctional structural composites whilst the methodology can easily be extended to identify optimal microstructural designs for other multifunctional material embodiments.

Hybrid graphene nanoplatelet/manganese oxide electrodes for solid-state supercapacitors and application to carbon fiber composite multifunctional materials

Abstract In this study, composite electrodes with hybrid formulation of graphene nanoplatelets and manganese oxide were fabricated. Graphene nanoplatelets modified with MnO2 particles under sonication in an organic solvent. The produced solution was utilized to form film electrodes on aluminum substrate and also to wet carbon fiber cloth in order to form multifunctional structural composite with energy storage ability. The morphology of the graphene nanoplatelet/manganese oxide electrodes was characterized by Scanning Electron Microscopy and Raman spectroscopy. Quasi solid-state electrolytes, consisted of different % wt. loadings of succinonitrile (SN), ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4) and copolymer poly vinylidenefluoride-hexafluoropropylene (PVDF-HFP), were prepared to be utilized as ionic conductors for the formation of supercapacitors. Differential scanning calorimetry (DSC) was used to characterize the thermal stability of the electrolytes. DSC studies confirmed that polymer electrolytes remain stable in the same phase over a wide temperature range of -40 to 140 °C. Also, mixture of epoxy and the quasi-solid polymer electrolyte was prepared to form a solid polymer electrolyte with higher stiffness. The electrochemical performance of the supercapacitor electrodes was evaluated by cyclic voltammetry, charge/discharge and impedance spectroscopy. The maximum value of specific capacitance achieved for the film electrodes was ˜450 F/g and for semi-solid and solid polymer electrolyte was ˜165 F/g and ˜15 F/g respectively. Finally, tensile tests performed at ambient conditions to determine the mechanical behavior of the supercapacitors. The results of this study are very promising for the development of materials with high combined performance in the field multifunctional composite structural materials with energy storage capabilities and can applied in a variety of industries such automotive, aerospace and wearable electronics.

Superplastic Air‐Dryable Graphene Hydrogels for Wet‐Press Assembly of Ultrastrong Superelastic Aerogels with Infinite Macroscale

AbstractHighly compressible graphene‐based monoliths with excellent mechanical, electrical, and thermal properties hold great potential as multifunctional structural materials to realize the targets of energy‐efficiency, comfort, and safety for buildings, vehicles, aircrafts, etc. Unfortunately, the ultralow mechanical strength and limited macroscale have hampered their practical applications. Herein, ultrastrong superelastic graphene aerogel with infinite macroscale is obtained by a facile wet‐press assembly strategy based on the novel superplastic air‐dryable graphene hydrogel (SAGH). The SAGH with isotropic, open‐cell, and highly porous microstructure is carefully designed by a dual‐template sol–gel method. Countless SAGH “bricks” can be assembled together orderly by press to form the strongly combined wet‐press assembled graphene aerogel (WAGA) “wall” after air‐drying. The WAGA with highly oriented, dense, multiple‐arch microstructure possesses arbitrary macroscale, outstanding compressive strength (47 MPa, over 10 times higher than the best ever reported), super elasticity (>97% strain), and high conductivity (378 S m−1). The strong adhesion is attributed to the tightly face‐to‐face contacted graphene interfaces caused by wet‐press and air‐drying. The WAGAs prove to be excellent multifunctional structural materials in the fields of high pressure/strain sensor, tunable mechanical energy absorber, high‐performance fire‐resistance, and thermal insulation. This facile strategy is easily extended to fabricate other similar metamaterials.

Nacre-mimetic composite with intrinsic self-healing and shape-programming capability

Replicating nacre’s multiscale architecture represents a promising approach to design artificial materials with outstanding rigidity and toughness. It is highly desirable yet challenging to incorporate self-healing and shape-programming capabilities into nacre-mimetic composites due to their rigidity and high filler content. Here, we report such a composite obtained by infiltrating a thermally switchable Diels-Alder network polymer into a lamellar scaffold of alumina. The chemical bond switchability and the physical confinement by the filler endows the composite with sufficient molecular mobility without compromising its thermal dimension stability. Consequently, our composite is capable of self-healing internal damages. Additionally, in contrast to the intractable planar shape of other artificial nacres, precise control of the polymer chain dynamics allows the shape of our composite to be programmed permanently via plasticity and temporarily via shape memory effect. Our approach paves a new way for designing durable multifunctional bioinspired structural materials.

Constructing interconnected graphene network in fluoroelastomer composites by F-H polar interaction for enhanced mechanical and barrier properties

Graphene is one of the most promising fillers for functional nanocomposites due to its high strength, high conductivity and high specific surface area, etc. However, its poor interfacial compatibility makes it difficult to simultaneously satisfy high strength and low gas permeability of nanocomposites. Herein, we proposed a novel strategy to regulate interfacial adhesion by fluorine-hydrogen (F-H) polar interaction in the FKM composites. The F-H polar interactions effectively induce the graphene oxide (GO) interact with the chain of fluoroelastomer (FKM) in spatial arrangements on molecular-level, promoting the construction of interconnected GO network. Specifically, a 10-fold increase in tensile strength of FKM/GO-5 with the incorporation of 5 phr GO is realized compared with pure FKM, and the oxygen permeability of FKM/GO-5 decreases by 79%. At the same filler contents, FKM/GO-5 composites exhibit higher mechanical property and lower gas permeability compared with FKM/rGO composites. Such enhanced performances make FKM/GO composites with an interconnected network very competitive for potential applications as multi-functional structural materials. The proposed strategy provides a novel effective approach for developing and designing the high-performances fluorine-based polymer nanocomposites.