Smart Materials Research Articles

Recent advances in responsive liquid crystal elastomer‐contained fibrous composites

AbstractResponsive polymers can react to surrounding environments by changing their physical and/or chemical properties. Among them, liquid crystal elastomers (LCEs) have emerged as one of the important branches in the field of applied polymer science due to their significant advantages in flexible mechanics and shape memory. Manufacturing LCE fibers with a large specific surface area and functional fillers has become a research hotspot in recent years. This type of LCE‐contained fibrous composite (LCEF) exhibits not only extremely high response sensitivity but also excellent axial mechanical strength and a high degree of deformation freedom. In this paper, we provide a bird's eye view of recent developments in LCEF, including structural designs, synthesis and forming methods, mechanical response principles and modes. Furthermore, we discuss recent advances of LCEF in artificial muscles, smart textiles, biomimetic systems, intelligent soft machines, followed by challenges and possible routes in fabrications and applications of LCEF. At the end, we aim to provide a perspective for an emerging field of stimulus‐responsive polymeric fiber composites.

Multiple covalent modification enables nylon fiber biosensor with robust scrub-resistant and signal-capture ability for multiscenario health monitoring and security warning

Nylon fibers have great potentials in smart textiles due to excellent wear resistance, resilience, and chemical stability, whereas poor combination between fibers and conductive materials causes discontinuous signal capture. In this work, nylon fibers/di-aldehyde cellulose nanocrystals/polypyrrole (NFACP) biosensors with robust scrub-resistant and signal-capture ability were fabricated by interfacial multiple covalent reactions. The best NFACP0.2 biosensor exhibited high conductivity (354 S/m), robust mechanical strength and stretching-releasing dynamic durability. Especially, its textile sensors still possessed high sensitivity and excellent sensing performance after repeated washing and friction. Moreover, NFACP0.2 biosensor was designed into various multifunctional health monitoring and security warning systems for “stress reducing exercise” enthusiasts, high-altitude activities, and deep-sea exploration, demonstating great potentials of conductive nylon fiber biosensor in flexible electronics.

Mechanical properties and damage mechanism of SMAHC laminates

Abstract The combination of smart materials and composite materials to achieve lightweight and intelligent structures has been an important research direction in recent years. In this paper, a three-dimensional woven hybrid shape memory alloy (SMA actuator) is modularly implanted into a composite laminate to prepare a SMA hybrid composite (SMAHC) laminate. The orthogonal test was designed with the three variables of SMA actuator modular implantation position, SMA pre-strain and SMA number. According to the orthogonal test results and finite element results, the influence of the three variables on the stiffness before heating, the stiffness change rate after heating and the strength of SMAHC laminates was studied. According to the test index, the influence of the three variables on the results was further evaluated. The results show that the implantation position has the greatest influence on the mechanical properties of SMAHC laminates, followed by SMA pre-strain, and the number of SMA has the least influence. The location and form of damage of SMAHC laminates are further summarized, and the bending damage mechanism of SMAHC laminates is analyzed.

Environmentally Friendly, Dual-Responsive Actuator Based on Nafion, Carboxylated Multiwalled Carbon Nanotubes, and Polyethylene.

As a type of smart material, flexible stimulus-responsive actuators have become a hot research topic nowadays. However, flexible actuators responding to a single stimulus source are susceptible to external perturbations, which may lead to an unstable function or even failure. Therefore, in this paper, we proposed a bilayer actuator that can be driven by both humidity and light by combining the humidity-sensitive Nafion, carboxylated multiwalled carbon nanotubes (cMWCNT) with excellent photothermal conversion properties, and commercial polyethylene (PE) tape with good humidity insensitivity and thermal expansion. First, the cMWCNT-Nafion film was prepared by a solution casting method and bonded together with PE tape to obtain a bilayer actuator. Then, the effects of the cMWCNT mass fraction and film thickness on the humidity and light response performance of the bilayer actuator were investigated. The optimal ratios of raw materials were obtained for different stimulation sources, respectively. Furthermore, the performance of the bilayer actuator with the optimal ratios was tested; it was verified that the proposed dual-responsive actuator can realize different degrees of bending deformation under different relative humidity (RH) and ultraviolet (UV) light intensity with good stability. Finally, the application potential in multiple scenarios was further verified by applying the prepared cMWCNT-Nafion/PE bilayer actuator to a smart window, crawling robot, and flexible gripper. This paper will provide a meaningful reference for the development and performance optimization of high-performance dual-responsive actuators.

Robo-Matter towards reconfigurable multifunctional smart materials

Maximizing materials utilization efficiency via enhancing their reconfigurability and multifunctionality offers a promising avenue in addressing the global challenges in sustainability. To this end, significant efforts have been made in developing reconfigurable multifunctional smart materials, which can exhibit remarkable behaviors such as morphing and self-healing. However, the difficulty in efficiently manipulating and controlling matter at the building block level with manageable cost and complexity, which is crucial to achieving superior responsiveness to environmental clues and stimuli, has significantly hindered the further development of such smart materials. Here we introduce a concept of Robo-Matter, which can be activated and controlled through external information exchange at the building block level, to enable a high-level of controllability, mutability and versatility for reconfigurable multifunctional smart materials. Using specially designed micro-robot building blocks with symmetry-breaking active motion modes, tunable anisotropic interactions, and interactive coupling with a programmable spatial-temporal dynamic light field, we demonstrate an emergent Robot-Matter duality, which enables a spectrum of desirable behaviors spanning from matter-like properties such as ultra-fast self-assembly and adaptivity, to robot-like properties including active force output, smart healing, smart morphing and infiltration. Our work demonstrates a promising direction for designing next-generation smart materials and large-scale robotic swarms.

State of art on evaluation of three- to six-dimensional novel additive manufacturing technology for biomedical applications

Additive manufacturing has evolved over the last few decades. Three-dimensional printing is a digital manufacturing technology that provides nearly endless options for the creation of an accessible instrument for all parts of various medical practices, including tissue engineering, through meticulous optimization of material, processing, and geometry for every point in an object. Three-dimensional printing has opened up a new, faster, and safer manufacturing process, despite its incapability to fabricate complex structures and objects. Recently, novel four-dimensional printing techniques have been developed for the transformation of typical stable three-dimensional printed parts into smart objects. The limitations of three-dimensional printing could be remedied with four-dimensional printing, by applying time as the fourth dimension. Self-repairing and speedy printing are two additional benefits of this technology's by using smart materials. By adapting this technology, numerous medical domains could be profited. Four-dimensional printing does not have the ability to produce curved complicated forms. However, five-dimensional printing overcomes the flaws seems in four-dimensional printing. Five-dimensional additive manufacturing relies on the rotation of both the print bed and the extruder head. Five-dimensional printing outlasts in terms of durability than three- and four-dimensional printing. Currently, a combination of the principles of four- and five-dimensional printing into a single process is called six-dimensional printing. In six-dimensional printing, the form changes over time due to the reaction of environmental factors, which is primarily used in biomedical applications. This paper summarizes extensive research on biomaterials in the field of biomedical science and discusses the present implications of three-, four-, five-, and six-dimensional printing techniques.

Electrospun Smart Hybrid Nanofibers for Multifaceted Applications.

Smart electrospun hybrid nanofibers represent a cutting-edge class of functional nanostructured materials with unique collective properties. This review aims to provide a comprehensive overview of the applications of smart electrospun hybrid nanofibers in the fields of energy, catalysis, and biomedicine. Electrospinning is a powerful tool to fabricate different types of nanofibers' morphologies with precise control over structure and compositions. Through the incorporation of various functional components, such as nanoparticles, nanomoieties, and biomolecules, into the (co)polymer matrix, nanofibers can be tailored into smart hybrid materials exhibiting responsiveness to external stimuli such as temperature, pH, or light among others. Herein recent advancements in fabrication strategies for electrospun smart hybrid nanofibers are discussed, focusing on different electrospinning tools aimed at tailoring and developing smart hybrid nanofibers. These strategies include surface functionalization, doping, and templating, which enable fine-tuning of mechanical strength, conductivity, and biocompatibility. The review explores the challenges and recent progress in the development of smart hybrid nanofibers. Issues such as scalability, reproducibility, biocompatibility, and environmental sustainability are identified as key for improvement. Furthermore, the applications of smart nanofibers in biomedicine, environment, energy storage, and smart textiles underscore their potential to address the challenges in development of nanostructured materials for emerging technologies.

Precisely Regulating Photoactivated Dynamic Room Temperature Phosphorescence by Alkyl Chain‐Induced Lattice‐Softening

AbstractDynamic response room temperature phosphorescence (RTP) is a hot topic in smart materials research due to its unique RTP‐response characteristics under external stimuli. However, its precisely control are currently challenging. Here, an alkyl chain‐induced lattice‐softening strategy is proposed to precisely regulate photoactivated dynamic RTP (PDRTP). By adjusting the alkyl chain flexibility of hybrid metal halide matrices, oxygen permeability can be adjusted, thereby achieving finely manipulate of the photoactivation equilibrium time, RTP lifetime, and RTP wavelength of the resulted host–guest doped materials within the ranges of 10–600 s, 0.05‐1.62 s, and 405–595 nm, respectively. It is also demonstrated the potential application of the PDRTP materials in afterglow oxygen sensing and multi‐level information encryption. This study not only proposes an effective method for regulating the photosensitivity of PDRTP materials, but also points out a new direction for exploring gas permeability in dense‐packed crystalline materials.

4D Printing of Multifunctional and Biodegradable PLA-PBAT-Fe3O4 Nanocomposites with Supreme Mechanical and Shape Memory Properties.

4D printing magneto-responsive shape memory polymers (SMPs) using biodegradable nanocomposites can overcome their low toughness and thermal resistance, and produce smart materials that can be controlled remotely without contact. This study presented the development of 3D/4D printable nanocomposites based on poly (lactic acid) (PLA)-poly (butylene adipate-co-terephthalate) (PBAT) blends and magnetite (Fe3O4) nanoparticles. The nanocomposites are prepared by melt mixing PLA-PBAT blends with different Fe3O4 contents (10, 15, and 20 wt%) and extruded into granules for material extrusion 3D printing. The morphology, dynamic mechanical thermal analysis (DMTA), mechanical properties, and shape memory behavior of the nanocomposites are investigated. The results indicated that the Fe3O4 nanoparticles are preferentially distributed in the PBAT phases, enhancing the storage modulus, thermal stability, strength, elongation, toughness, shape fixity, and recovery of the nanocomposites. The optimal Fe3O4 loading is found to be 10 wt%, as higher loadings led to nanoparticle agglomeration and reduced performance. The nanocomposites also exhibited fast shape memory response under thermal and magnetic activation due to the presence of Fe3O4 nanoparticles. The 3D/4D printable nanocomposites demonstrated multifunctional multi-trigger shape-memory capabilities and potential applications in contactless and safe actuation.

Identification of stiffness and damping characteristics of magnetorheological elastomers due to immersion in seawater

ABSTRACT Magnetorheological elastomer (MRE) materials are commonly used as vibration dampers in offshore structures. Therefore, it is urgent to investigate the degradation of this smart material because of seawater interaction. This work focuses on the immersion of MRE material in seawater, which alters its rheological and mechanical characteristics. Hence, it is important to investigate the impact of seawater immersion on the rheological characteristics of substances. This study contributes to the assessment of the stiffness and damping characteristics of MRE materials after exposure to seawater for one year. The MRE samples comprise MRE with a silicone matrix devoid of any Carbonyl Iron Particle (CIP) and MRE with 70% CIP, exhibiting both isotropic and anisotropic properties. Immersing the subject in seawater was carried out for one year. The study involved doing multiple tests, such as scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and rheological testing. The findings indicated that the samples underwent harm, erosion, and deterioration of their rheological characteristics during immersion. The stiffness values for isotropic MRE and anisotropic MRE decreased by 97% and 11%, respectively. Meanwhile, the deterioration of the damping characteristics values of isotropic MRE and anisotropic MRE was 96% and 14%, respectively.

Multiprogrammable Anisotropic Soft Material via Magneto‐Orientation of Ferromagnetic Nanoplates

AbstractAnisotropic materials featured with ordered arrangement of sub‐structures are ubiquitous in living organisms, and possess rapidly increasing relevance to emerging technologies in smart materials, soft robotics, flexible displays, and biomedicines. However, the integration and programming of multiple properties into anisotropic materials, which endow themselves with extended intrinsic capabilities and utilities, still remain a challenge. Herein, we report a multi‐programmable anisotropic material by embedding ferromagnetic two‐dimensional nanoplates into hydrogel matrix. The nanoplate exhibits not only a disc‐like non‐isotropic shape, but also an intrinsic easy magnetization axis perpendicular to its basal plane. Using a directional external magnetic field, we can precisely control the orientation of nanoplates inside hydrogel precursor solution and then fix them via photolithographic polymerization, leading to the fabrication of anisotropic hydrogel with on‐demand ordered alignment of nanoplates. Such deliberate arrangement of nanoplates brings in extraordinary optical properties due to birefringence, enabling us to encrypt pattern information into hydrogel materials that is only visible under polarized light. Soft actuators with programmable optical, mechanical and magnetic properties are engineered, which allow to encode diverse deformation and locomotion modes, determine the actuation sites, and monitor the sub‐structural anisotropy all simultaneously, opening new avenues for the design of anisotropic soft materials.

Development of a Smart Material Resource Planning System in the Context of Warehouse 4.0

Development of a Smart Material Resource Planning System in the Context of Warehouse 4.0

Light-Controlled Interconvertible Self-Assembly of Non-Photoresponsive Suprastructures

Achieving light-induced manipulation of controlled self-assembly in nanosized structures is essential for developing artificially dynamic smart materials. Herein, we demonstrate an approach using a non-photoresponsive hydrogen-bonded (H-bonded) macrocycle to control the self-assembly and disassembly of nanostructures in response to light. The present system comprises a photoacid (merocyanine, 1-MEH), a pseudorotaxane formed by two H-bonded macrocycles, dipyridinyl acetylene, and zinc ions. The operation of such a system is examined according to the alternation of self-assembly through proton transfer, which is mediated by the photoacid upon exposure to visible light. The host–guest complexation between the macrocycle and bipyridium guests was investigated by NMR spectroscopy, and one of the guests with the highest affinity for the ring was selected for use as one of the components of the system, which forms the host–guest complex with the ring in a 2:1 stoichiometry. In solution, a dipyridine and the ring, having no interaction with each other, rapidly form a complex in the presence of 1-MEH when exposed to light and thermally relax back to the free ring without entrapped guests after 4 h. Furthermore, the addition of zinc ions to the solution above leads to the formation of a polypseudorotaxane with its morphology responsive to photoirradiation. This work exemplifies the light-controlled alteration of self-assembly in non-photoresponsive systems based on interactions between the guest and the H-bonded macrocycle in the presence of a photoacid.

Carbazole-isonicotinoyl Hydrazone and Its Structurally Distinct Zinc(II) Complexes as Reversible Mechanochromic, Mechanofluorochromic, and Acidochromic Smart Materials

Carbazole-isonicotinoyl Hydrazone and Its Structurally Distinct Zinc(II) Complexes as Reversible Mechanochromic, Mechanofluorochromic, and Acidochromic Smart Materials

Fabrication and Performance of a Silver Nanowire Silk Conductive Fabric.

In this work, silk was selected as the substrate, and formic acid was utilized to create a rough texture on the silk. The conductive fabrics made from AgNWs and silk were created by applying multiple layers of silver nanowire dispersion onto the textured silk fabrics (SFs). The silk was immersed in a dispersion containing polydopamine (PDA), sericin (SE), tannic acid (TA), and silver nanowire under specific temperature conditions. After being cured at 120 °C, the three silver nanowire/silk fabrics (AgNWs/SFs), PDA/AgNWs/SF, SE/AgNWs/SF, and TA/AgNWs/SF, exhibited square resistances of 7.37, 540, and 200 Ω/sq, respectively. The method used to prepare the AgNW conductive SF is straightforward, resulting in fabrics that possess excellent thermal stability and resistance to washing. These fabrics also exhibit a range of useful properties, including conductivity, electrothermal capabilities, electrochemical functionality, human body sensing, hydrophobicity, and antimicrobial properties. These characteristics make them highly promising for various applications, such as human body motion detection, electronic textiles, electrothermal textiles, and antimicrobial applications.

Excitation-wavelength-dependent persistent luminescence from single-component nonstoichiometric CaGaxO4:Bi for dynamic anti-counterfeiting

Materials capable of dynamic persistent luminescence (PersL) within the visible spectrum are highly sought after for applications in display, biosensing, and information security. However, PersL materials with eye-detectable and excitation-wavelength-dependent characteristics are rarely achieved. Herein, a nonstoichiometric compound CaGaxO4:Bi (x < 2) is present, which demonstrates ultra-long, color-tunable PersL. The persistent emission wavelength can be tuned by varying the excitation wavelength, enabling dynamic color modulation from the green to the orange region within the visible spectrum. Theoretical calculations, in conjunction with experimental observations, are utilized to elucidate the thermodynamic charge transitions of various defect states, thereby providing insights into the relationship between Bi3+ emitters, traps, and multicolored PersL. Furthermore, the utility of color-tunable PersL materials and flexible devices is showcased for use in visual sensing of invisible ultraviolet light, multicolor display, information encryption, and anti-counterfeiting. These discoveries create new opportunities to develop smart photoelectric materials with dynamically controlled PersL for various applications.

Mechanical and shape-memory properties of TPMS with hybrid configurations and materials

ABSTRACT Triply periodic minimal surface (TPMS) structures with excellent properties of stable energy absorption, light weight, and high specific strength could potentially spark immense interest for novel and programmable functions by combining smart materials, e.g. shape memory polymers (SMPs). This work proposes TPMS lattices with hybrid configurations and materials that are composed of viscoelastic and shape-memory materials with the aim to bring temperature-dependent mechanical properties and additional dissipation mechanisms. Different configurations and diverse materials of polylactic acid (PLA), fiber-reinforced PLA, and polydimethylsiloxane (PDMS) are induced, generating five types of TPMS lattices, including (Schoen’s I-WP) IWP uniform lattice, IWP lattice with density gradient, hybrid configurations, hybrid materials, and filled PDMS, which are fabricated by 3D printing. The fracture morphologies and the distribution of carbon fibers are demonstrated via scanning electron microscopy with a focus on the influence of carbon fiber on shape-memory and mechanical properties. Shape recovery tests are conducted, which proves good shape memory properties and reusable capability of TPMS lattice. The combined methods of experiments and numerical simulation are adopted to evaluate mechanical properties, which presents multi-stage energy absorption ability and tunable vibration isolation performances associated with temperature and hybridization designs. This work can promote extensive research and provide substantial opportunities for TPMS lattices in the development of functional applications.

Active-type piezoelectric smart textiles with antifouling performance for pathogenic control

Recently, an investigation into preventive measures for coronavirus disease 2019 (COVID-19) has garnered considerable attention. Consequently, strategies for the proactive prevention of viral pathogens have also attracted significant interest in the field of wearable devices and electronic textiles research, particularly due to their potential applications in personal protective equipment. In this study, we introduce smart textiles designed with optimized piezoelectric devices that exhibit antifouling performance against microorganisms and actively inactivate viruses. These active-type smart textiles, which incorporate advanced lead zirconate titanate (PZT) ceramics, a stretchable interconnector array, and polymeric fabric, demonstrate effective antifouling capabilities, detaching approximately 90% of Escherichia coli and 75% of SARS-CoV-2. Furthermore, they inactivate viruses, releasing ~26.8 ng of N protein from ruptured SARS-CoV-2, using ultrasonic waves within the wearable platform. Experimental results show that piezoelectric smart textiles significantly reduce the spread of COVID-19 by leveraging the electrical and acoustic properties of PZT ceramics.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis.

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Supramolecular Luminescent Hydrogel Based on Glycine/Terbium Complex and Fluorescent Dyes for Visual Temperature Monitoring

AbstractThe development of smart synthetic materials that are sensitive, accurate, and visually responsive to changes in temperature is vital. Herein, a supramolecular luminescent hydrogel based on a glycine/terbium (Gly/Tb) complex, rhodamine B (RB), and gelatin is reported. The hydrogel exhibits responsive luminescence and undergoes a temperature‐induced phase transformation from hydrogel to sol. The electrospray ionization time‐of‐flight mass spectra, Fourier‐transform infrared spectra, and simulation results verifiy the coordination mode of the Gly/Tb complex. The Gly/Tb complex and RB emit green and orange luminescence, respectively. When the Gly/Tb complex and RB are co‐doped into the gel network of gelatin, the obtained Gly/Tb/RB hydrogel displays steady yellow luminescence by virtue of luminescence resonance energy transfer. Subsequently, a luminescent switch is constructed owing to the sensitive and reversible luminescence responsiveness of the Gly/Tb/RB hydrogel to temperature stimuli. Remarkably, the Gly/Tb/RB hydrogel undergoes a visual phase transformation from hydrogel to sol above 35 °C, allowing the ambient temperature variation to be monitored. This study establishes a novel and effective route for the construction of smart optical materials and visual temperature monitors.