Application Of Smart Materials Research Articles

Multi-flexible organic crystal responding to different mechanical forces for flexible optical waveguides

Organic crystals with flexibility have been a research hotspot due to their huge potential in flexible optoelectronics. However, most organic crystals are brittle, which greatly restricts their application in flexible smart materials. Herein, a flexible crystal with multi-faced elastic bending and plastic twisting was reported. Even after undergoing severe twisting deformation, it could be freely bent in any direction due to the twisted shape, thus achieving the transition to three-dimensional (3D) elastic bending. The mechanisms of multiple flexibilities were investigated by detailed experimental analysis and theoretical calculations. Especially, the mechanism of twistable crystals with elasticity was well revealed by microfocus spectroscopy and theoretical calculation, which has not been reported before. It was found that the twisting of organic crystals can be attributed to the molecular rotation without spatial hindrance, abundant weak intermolecular interactions and different orientations of the intermolecular interactions. Finally, taking advantage of its flexibility, its potential application in flexible active and passive optical waveguides was demonstrated.

A highly conductive polymer composite with enhanced stretchability and long-term stability for wearable electronic applications

In this study, we investigate the impact of incorporating poly(acrylic acid) (PAA) as a soft polymer on the long-term stability and flexibility (or stretchability) of a highly conductive composite consisting of hydroquinone (HQ)-modified Poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (HQ-PEDOT:PSS). Our findings demonstrate that PAA can effectively act as a steric hindrance barrier between conductive-PEDOT and insulative-PSS, thus improving the stability of the composite over time. Furthermore, the PAA mixture minimizes the conductivity decrease compared to other representative hydrophilic soft polymers, such as poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP). With the addition of 2 wt% PAA to HQ-PEDOT:PSS, the composite exhibits significantly higher conductivity (290 S/cm) compared to PVA (42 S/cm) and PVP (10−3 S/cm). The HQ-PEDOT:PSS/PAA composite also displays excellent stretchability, with a sharp strain response followed by a drastically enhanced gauge factor over a wide strain range (10%–50%). As a result, the composite shows great potential as a strain sensor, with high sensitivity for detecting diverse body motions. Moreover, due to its high conductivity, the composite exhibits high sensitivity for detecting human electrocardiogram (ECG) signals, with negligible degradation of signal intensity even one month after fabrication. Overall, our results suggest that the HQ-PEDOT:PSS/PAA conductive composite has significant potential for wearable smart textile applications, enabling diverse body motion and vital sign sensing.

Preparation and Characterization of Non-Crimping Laminated Textile Composites Reinforced with Electrospun Nanofibers.

This research investigated the use of electrospun nanofibers as reinforcing laminates in textiles to enhance their mechanical properties for use as smart and technical textile applications. Crimping plays a crucial role in textiles. Because of crimp, fabrics have extensibility, compressibility, and improved quality. Although crimping is inevitable for fabrics used in smart textiles, it is also a disadvantage as it could weaken the fibers and reduce their strength and efficiency. The study focused on preparing laminated textile composites by electrospinning a polyacrylonitrile (PAN) polymer onto textile fabric. The research examined the effect of electrospun nanofibers on the fabric by using a tensile testing machine and scanning electron microscopy. The results revealed that the prepared laminated textile was crimp-free because of the orientation of the nanofibers directly electrospun on the fabric, which exhibited perfect bonding between the laminates. Additionally, the nanofiber-reinforced composite fabrics demonstrated a 75.5% increase in the elastic moduli and a 20% increase in elongation at breaking. The study concluded that the use of electrospun nanofibers as laminates in textile composites could enhance the elastic properties, and prepared laminated composites will have the advantages of nanofibers, such as crimp-free elastic regions. Furthermore, the mechanical properties of the laminated textile composite were compared with those of the micromechanical models, providing a deeper understanding of the behavior of these laminated composites.

Late‐Stage Photocatalytic Fluoroalkylation of Aromatic Crown Ethers in Aqueous Media

AbstractModified crown ethers are fundamental building blocks in supramolecular chemistry, with applications in phase transfer catalysis, metal extraction, smart materials, and molecular machines. Here we report on a one‐pot highly chemo‐ and regioselective photocatalytic fluoroalkylation protocol for the mono‐functionalization of benzo substituted crown ethers. For this important class of macrocycles, the method described here represents one of the few late‐stage functionalization procedures that is both high yielding and scalable. Because of its breadth of scope and substrate tolerance, the devised approach can be applied to a wide range of aromatic crown ethers (18 examples, up to 99 % yield), including those engaged in mechanically interlocked molecules.

Mechanical and thermal properties of polyamide‐6 nanocomposites reinforced by graphene oxide with low loading by double extrusion method

AbstractThe high toughness, high abrasion resistance, and high water absorption capacity of polyamide‐6 (PA6), and the restacking of graphene oxide (GO) sheets make it quite challenging to get uniformly dispersed GO/PA6 nanocomposites. Herein, GO of different parts per hundred ratios (phr) was melt‐mixed with PA6 matrix by double extrusion using a twin‐screw compounder, followed by the micro twin‐screw extruder, and composites were prepared by injection molding method. The stress–strain curves from tensile measurements showed strain hardening in nanocomposites. The yield strength and Young's modulus increased by 11.3% and 16.7% respectively, for 0.1 phr GO loading. The crystallization and melting temperatures in differential scanning calorimetry (DSC) were increased by 4.7 and 9.6°C, respectively with 0.1 phr GO reinforcement. The Raman and XRD analysis showed continuous shifting in the intensity peaks with increasing reinforcements. Moreover, a double extrusion process imparts good mechanical and thermal stability to our composites. The significant improvement in mechanical and thermal performance of injection molded nanocomposites at very low reinforcements leads to their potential applications in automobiles, civil constructions, smart textiles, packaging, and sensors.

Asymmetric-elastic-structure fabric-based triboelectric nanogenerators for wearable energy harvesting and human motion sensing

With rapid advancement in wearable electronics, triboelectric nanogenerators (TENGs) have attracted great attention for energy harvesting and bio-motion sensing because of low cost, environmentally friendly, safe, sustainable and easy availability. However, the existing structure is not well suitable and desirable for ordinary apparel. There are great challenges in balancing structural and motion adaptability with high-performance output for practical wearable applications. Therefore, herein we ingeniously combine human motions and the difference in elasticity between fabrics to develop an asymmetric-elastic-structure fabric-based triboelectric nanogenerator (AesF-TENG) which can realize rapid contact and separation under small deformation or force, and can efficiently harvest the mechanical energy under the natural motion of the human body to obtain better wearable potential. The AesF-TENG is composed of nylon and doped polydimethylsiloxane (PDMS) used as positive and negative triboelectric materials respectively, and stretchable elastic fabric and conventional cotton fabric as the base. The developed AesF-TENG can efficiently harvest biomechanical energy and maintain stable electrical performance after 20 washes and 120,000 durability tests and also drive commercial electronic watch, calculator and LEDs. Additionally, it could be also utilized as a self-powered wearable sensor for wireless monitoring of human body motions. The prominent output power performance of AesF-TENG together with human motion and textiles show their great potentials for viable applications in wearable electronics and smart textiles in the near future.

The Prandtl–Ishlinskii Hysteresis Model: Fundamentals of the Model and Its Inverse Compensator [Lecture Notes

Hysteresis is a nonlinear phenomenon arising in diverse fields such as mechanics, biology, electronics, and economics <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> (see “Summary”). In particular, hysteresis is ubiquitously exhibited by various smart materials, such as piezoelectrics, magnetostrictives, and shape memory alloys <xref ref-type="bibr" rid="ref2" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</xref> , <xref ref-type="bibr" rid="ref3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[3]</xref> . These materials show inherent coupling between mechanical properties and electrical/magnetic/thermal fields; therefore, they can be used as sensors and actuators. For different smart material applications, hysteresis is a main source of nonlinearity, which creates challenges in the control of these systems.

Copper-Coordinated Cellulose Fibers for Electric Devices with Motion Sensitivity and Flame Retardance.

Nanocomposite conductive fibers are of great significance in applications of wearable devices, smart textiles, and flexible electronics. Integration of conductive nanomaterials into flexible bio-based fibers with multifunctionality remains challenging due to interface failure, poor flexibility, and inflammability. Although having broader applications in textiles, regenerated cellulose fibers (RCFs) cannot meet the requirements of wearable electronics owing to their intrinsic insulation. In this study, we constructed conductive RCFs fabricated by coordinating copper ions with cellulose and reducing them into stable Cu nanoparticles coated on their surface. The Cu sheath offered excellent electrical conductivity (4.6 × 105 S m-1), electromagnetic interference shielding, and enhanced flame retardance. Inspired by plant tendrils, the conductive RCF was wrapped around an elastic rod to develop wearable sensors for human health and motion monitoring. The resultant fibers not only form stable conductive nanocomposites on the fiber surface by chemical bonds but also exhibit a huge potential for wearable devices, smart sensors, and flame-retardant circuits.

Novel Quaternary CuAlZnMg High Temperature Shape Memory Alloy (HTSMA) Fabricated by Minor Batch of Zn and Mg Additions

Shape memory alloys (SMAs) constitute the second largest commercial smart material class after piezoelectric materials. Different SMA alloy systems or SMAs with miscellaneous functionalities and characteristic properties have been designed for using in different applications until today. High temperature shape memory alloys (HTSMAs) are also widely desired to be used in various smart materials applications. HTSMAs with different functional and characteristic properties are muchly demanded for different tasks to be done by these alloys or devices designed by these alloys. A common and practical way to fabricate SMAs or HTSMAs with different shape memory effect (SME) and other properties is to fabricate them with different alloying compositions and add different additive elements. In this work, a quaternary CuAlZnMg HTSMA with an unprecedented composition consisting minor amount of zinc and magnesium additives was produced by arc melting method. As a result of applying post-homogenization in high β–phase temperature region and immediate quenching, the microstructural mechanism of a SME property was formed in the produced alloy. After then, to examine SME characteristics of the CuAlZnMg alloy some differential thermal analysis (DTA), microstructural (XRD) and magnetization (VSM) characterization tests were carried out. The DTA results showed that the alloy is a HTSMA exhibiting reverse martensitic transformations at temperature range between 167 °C and 489 °C. The XRD pattern obtained at room temperature revealed the martensite phases formed in the alloy, which phases are the base mechanism of the reversible martensitic transformation (the SME property) of the alloy. The VSM test showed that the alloy exhibit a diamagnetic property with a weak ferromagnetic coercivity contribution.

BODIPY as a Multifunctional Theranostic Reagent in Biomedicine: Self-Assembly, Properties, and Applications.

The use of boron dipyrromethene (BODIPY)inbiomedicineisreviewed.To open, its synthesis and regulatory strategies are summarized, and inspiring cutting-edge work in post-functionalization strategies is highlighted. A brief overview of assembly model of BODIPY is then provided: BODIPY is introduced as a promising building block for the formation of single- and multicomponent self-assembled systems, including nanostructures suitable for aqueous environments, thereby showing the great development potential of supramolecular assembly in biomedicine applications. The frontier progress of BODIPY in biomedical application is thereafter described, supported by examples of the frontiers of biomedical applications of BODIPY-containing smart materials: it mainly involves the application of materials based on BODIPY building blocks and their assemblies in fluorescence bioimaging, photoacoustic imaging, disease treatment including photodynamic therapy, photothermal therapy, and immunotherapy. Lastly, not only the current status of the BODIPY family in the biomedical field but also the challenges worth considering are summarized. At the same time, insights into the future development prospects of biomedically applicable BODIPY are provided.

Dielectric Elastomer Cooperative Microactuator Systems—DECMAS

This paper presents results of the first phase of “Dielectric Elastomer Cooperative Microactuator Systems” (DECMAS), a project within the German Research Foundation Priority Program 2206, “Cooperative Multistable Multistage Microactuator Systems” (KOMMMA). The goal is the development of a soft cooperative microactuator system combining high flexibility with large-stroke/high-frequency actuation and self-sensing capabilities. The softness is due to a completely polymer-based approach using dielectric elastomer membrane structures and a specific silicone bias system designed to achieve large strokes. The approach thus avoids fluidic or pneumatic compo-nents, enabling, e.g., future smart textile applications with cooperative sensing, haptics, and even acoustic features. The paper introduces design concepts and a first soft, single-actuator demonstrator along with experimental characterization, before expanding it to a 3 × 1 system. This system is used to experimentally study coupling effects, supported by finite element and lumped parameter simulations, which represent the basis for future cooperative control methods. Finally, the paper also introduces a new methodology to fabricate metal-based electrodes of sub-micrometer thickness with high membrane-straining capability and extremely low resistance. These electrodes will enable further miniaturization towards future microscale applications.

Flexible, stripe-patterned organic solar cells and modules based on multilayer-printed Ag fibers for smart textile applications

Rapid advancement in the fabrication technologies of stripe/fiber-shaped optoelectronic devices has driven the performance of smart textile electronics to a new height. In the development of high-performance smart textile electronics, indium tin oxide (ITO)-free flexible transparent conductive electrodes (TCEs) are particularly desirable because they offer superior flexibility and lower manufacturing cost than the brittle ITO-based counterparts. Herein, we innovatively combine spin-coating and three-dimensional direct-ink writing (three-dimensional-DIW) techniques to develop large-area (5 × 5 cm2) PEDOT:PSS/Ag-fibers hybrid TCEs (denoted as DIW-TCEs) for application in flexible organic solar cells (OSCs). Through a multilayer printing strategy, high aspect-ratio Ag-fibers are successfully deposited on top of the planar PEDOT:PSS film. The resulting DIW-TCEs, when fully embedded in a colorless polyimide substrate, exhibit excellent electrical conductivity (sheet resistance ∼ 4 Ω/□), superior optical transmittance, and mechanical flexibility. One-dimensional stripe-patterned OSCs (stripe-OSCs) based on DIW-TCEs achieved power conversion efficiency of 9.3% and 8.2% at an active area of 0.11 cm2 and 0.31 cm2, respectively. For real-life application, a flexible power module was constructed using eight stripe-OSCs. When attached on textile, the module successfully lit up a commercial light-emitting diode upon photocharging. The unique DIW-TCE fabricated herein can be the ITO-free alternative for the production of smart textile electronics.

A highly flame-retardant, agile fire-alarming and ultrasensitive cotton fabric-based piezoresistive sensor for intelligent fire system

With the high frequency of fires, multifunctional cotton fabrics with high flame retardancy and agile fire-warning ability are urgently needed. Herein, a newly cotton fabric-based piezoresistive sensor (denoted as CF@A-CNTs/APP) with intelligent fire protection and high sensitivity is proposed, which is composed of amino-functionalized carbon nanotubes (A-CNTs) and ammonium polyphosphate (APP) wrapped on cotton fabric (CF) using layer-by-layer self-assembly. The CF@A-CNTs/APP demonstrated excellent flame retardancy due to the synergistic formation of a dense flame retardant layer on the CF surface by A-CNTs and APP. The char residue of CF@A-CNTs/APP reached 44.0 wt% at 700 °C (nitrogen atmosphere), and the limiting oxygen index of CF@A-CNTs/APP was as high as 37.6%. More importantly, the CF@A-CNTs/APP triggered the fire-alarming system within 2 s. Benefiting from the pattern microstructures of double-layers CF and the high conductivity of A-CNTs, the CF@A-CNTs/APP has exhibited a high sensitivity of 3.8 kPa−1 (0 kPa-16.62 kPa). In view of outstanding flame retardancy, high sensitivity and robustness, the CF@A-CNTs/APPs could be integrated into firefighting suits or electronic skins to monitor the behavioral actions and equipment operating conditions. This work provides a novel strategy for a new generation of CF-based sensors with fire resistance and high sensitivity, and offers new insights into the preparation and application of smart fire-resistant materials in the field of the internet of things.

Complex dispersion relations and evanescent waves in periodic magneto-electro curved phononic crystal plates

This paper presents a novel semi-analytical method to consider complex dispersion relations and evanescent wave characteristics in periodic magneto-electro-electric curved phononic crystal plates, based on the plate theory and Bloch-Floquet theorem. Generalized elastodynamic wave equation considering the magneto-electric effects in cylindrical coordinate system is established and discretized with the curved higher-order spectral elements. Then, the proposed approach is validated by the analysis of accuracy and convergence. The influence of magneto-electro coupling effect on dispersion relations are discussed. Significant parameters of the periodic curved phononic crystal are studied systematically, which fundamentally determines the tunability of complex dispersion relations of various guided wave modes including propagative wave modes, purely evanescent wave modes, evanescent edge wave modes, and complex wave modes. It is witnessed that propagative wave modes lead the bandgap to the emergence, variation, and closure with the change of significant parameters. And evanescent wave modes dominate two individual patterns of bandgaps. When the radius angle or curvature changes, the polarization of bandgaps appears. Furthermore, complex wave modes are generated with the increase of curvature resulting in strengthening the attenuation of propagative wave modes. The variation of lattice ratio can separate the intersection point of two propagative wave modes, which induces the opening of two bandgaps and the attenuation of evanescent wave modes. The results of this work provides may benefit the multi-functional development and application of smart materials and structures.

Solvent-induced MultiStimuli-Responsive properties of cyano-substituted Oligo(p-phenylene vinylene) derivatives

Stimuli-responsive luminescent materials with controllable photophysical properties have attracted much attention because of their potential applications in smart materials and devices. Through the incorporation of electron-donating (NPh3) and electron-withdrawing (CN) functionalities, two donor-acceptor luminophores C4OPV-TPA and C8OPV-TPA bearing two different alkyl chain lengths were prepared and fully characterized. Although both C4OPV-TPA and C8OPV-TPA exhibited similar luminescence and AIEE effects in solution with intramolecular charge-transfer (ICT) transition, remarkable differences were observed in the self-assemble state. Specifically, precipitation of C4OPV-TPA into toluene and CH2Cl2, respectively, afforded two distinctly crystallines, with one in orange color (O-state) and the other in red color (R-state). Notably, C4OPV-TPA in O-state exhibited stimuli-responsive behaviors in solid state, which were ascribed to the formation of an inclusion complex with toluene molecules. Under thermal heating and mechanical grinding, toluene was released from crystal lattice of luminophore accompanied with red-shifted emission spectra. The molecular packing of C4OPV-TPA in R-state, on the other hand, adopted stronger H-aggregates without inclusion of CH2Cl2 molecules, which was further investigated by X-ray diffraction. These excellent optical properties enabled C4OPV-TPA serve as a fluorescent ink for thermal-responsive data storage device.

Low specific absorption rate quad-port multiple-input-multiple-output limber antenna integrated with flexible frequency selective surface for WBAN applications

This paper presents the design and analysis of a multiple-input-multiple-output (MIMO) textile antenna for wireless body area network (WBAN) applications. The MIMO antenna is comprised of four identical modified rhombus-shaped monopole antenna elements of size of 0.57, where is the wavelength calculated at the lowest operating frequency. The antenna is backed by a 6 frequency selective surface (FSS) of dimensions of 0.84 to improve gain and to reduce specific absorption rate (SAR). The antenna has an impedance bandwidth (S 11 ⩽ −10 dB) of 8.8 GHz (2.8–11.6 GHz) and isolation of >19 dB between the resonating elements. In order to assess the MIMO antenna’s flexibility, the bending analysis is performed for various bending radii. The obtained diversity metrics are: envelope correlation coefficient <0.5 dB, diversity gain <10 dB, channel capacity loss <0.4 bits s−1 Hz−1, and total active reflection coefficient <−10 dB. The performance of the antenna with and without FSS is investigated for gain enhancement and SAR reduction. With the help of FSS, the antenna gain is increased to 8.44 dBi, and the SAR reduced from 6.99 Watt kg−1 to 0.0273 Watt kg−1. The FSS achieves the highest efficiency of 96%. The designed antenna is suitable for smart textile applications due to its low SAR, high gain, and wider impedance bandwidth.

PVDF nanofibers composite containing core-shell (ZnO@ZIF-8) for use in smart textile applications

PVDF nanofibers composite containing core-shell (ZnO@ZIF-8) for use in smart textile applications

Piezo-resistive Properties of Polymer based cement nano composites

The nano technology has potential applications in development self-sensing smart materials. These nano materials is used in cement matrix or polymer base to improve the mechanical and piezo electrical properties of composites. In the present study, the graphene and carbon nano tube are added in matric, which acts as the conductive fibre into polymer cement composites. Cement based polymer composites are prepared by adding carbon fibre, epoxy resin, carbon nano tube and graphene as conductive filler in matrix to prepare the distinctive specimens for experimental investigations. The electro mechanical test are carried out to assess the piezo electrical properties of these composites subjected gradual increase of mechanical loading such as flexural and compression. The present study describes the self-sensing piezo-resistive capability of composite to monitor the strain in structures. The experimental test elucidates the addition of epoxy in cement matrix enhance the mechanical properties while carbon nano tube and graphene proves to be promising smart self-sensing materials in composites by measuring the variation in stress at critical regions. The SEM with EDX analysis shows that epoxy resin act as binding agent which hinder the cracks propagations and improves the mechanical properties of composites.

Manipulating fluorescence by photo-switched spin-state conversions in an iron(ii)-based SCO-MOF.

Manipulating fluorescence by photo-switched spin-state conversions is an attractive prospect for applications in smart magneto-optical materials and devices. The challenge is how to modulate the energy transfer paths of the singlet excited state by light-induced spin-state conversions. In this work, a spin crossover (SCO) FeII-based fluorophore was embedded into a metal-organic framework (MOF) to tune the energy transfer paths. Compound 1 {Fe(TPA-diPy)[Ag(CN)2]2}·2EtOH (1) has an interpenetrated Hofmann-type structure, wherein the FeII ion is coordinated by a bidentate fluorophore ligand (TPA-diPy) and four cyanide nitrogen atoms and acts as the fluorescent-SCO unit. Magnetic susceptibility measurements revealed that 1 underwent an incomplete and gradual spin crossover with T1/2 = 161 K. Photomagnetic studies confirmed photo-induced spin state conversions between the low-spin (LS) and high-spin (HS) states, where the irradiation of 532 and 808 nm laser lights converted the LS and HS states to the HS and LS states, respectively. Variable-temperature fluorescence spectra study revealed an anomalous decrease in emission intensity upon the HS → LS transition, confirming the synergetic coupling between the fluorophore and SCO units. Alternating irradiation of 532 and 808 nm laser lights resulted in reversible fluorescence intensity changes, confirming spin state-controlled fluorescence in the SCO-MOF. Photo-monitored structural analyses and UV-vis spectroscopic studies demonstrated that the photo-induced spin state conversions changed energy transfer paths from the TPA fluorophore to the metal-centered charge transfer bands, ultimately leading to the switching of fluorescence intensities. This work represents a new prototype compound showing bidirectional photo-switched fluorescence by manipulating the spin states of iron(ii).

Coating Machine Developed for Technical and Smart Textile Applications

In today's textile industry, besides products that appeal to fashion, functional technical and smart textile products obtained by integrating many technologies into clothing are in demand. Many functional properties such as antibacterial, heat and electrical conductivity can be applied to yarns and fabrics by production methods such as impregnation, exhaust, etc. However, the current yarn coating technology has disadvantages such as inability to make homogeneous coating with different chemicals and low coating durability. In this study, the coating process was carried out in a yarn coating machine, which was developed to allow one-wire coating from bobbin to bobbin, which is the first in the sector, and the effect of the coating method on the yarn properties was evaluated by examining the performance characteristics.&#x0D;