Multifunctional Material Systems Research Articles

Taming Multiscale Structural Complexity in Porous Skeletons: From Open Framework Materials to Micro/Nanoscaffold Architectures.

Recent developments in the design and synthesis of more and more sophisticated organic building blocks with controlled structures and physical properties, combined with the emergence of novel assembly modes and nanofabrication methods, make it possible to tailor unprecedented structurally complex porous systems with precise multiscale control over their architectures and functions. By tuning their porosity from the nanoscale to microscale, a wide range of functional materials can be assembled, including open frameworks and micro/nanoscaffold architectures. During the last two decades, significant progress is made on the generation and optimization of advanced porous systems, resulting in high-performance multifunctional scaffold materials and novel device configurations. In this perspective, a critical analysis is provided of the most effective methods for imparting controlled physical and chemical properties to multifunctional porous skeletons. The future research directions that underscore the role of skeleton structures with varying physical dimensions, from molecular-level open frameworks (<10nm) to supramolecular scaffolds (10-100nm) and micro/nano scaffolds (>100nm), are discussed. The limitations, challenges, and opportunities for potential applications of these multifunctional and multidimensional material systems are also evaluated in particular by addressing the greatest challenges that the society has to face.

Challenges and Trends for Multifunctional Materials

Materials science is the study of materials, their properties and their applications. As the rapid development of material science, materials tend to approach multifunctionality. Multifunctional materials are designed to perform multiple responsibilities through prudent combinations of different functional capabilities. Typically, each function contributes a distinct physical or chemical process that can deliver system-level improvements beyond the status quo. Even though some researchers have defined "smart material" as multifunctional materials (MFM), multifunctional composites (MFC), multifunctional structures (MFS), and multifunctional material systems (MFMS), the term "multifunctional materials" will be used to refer to all of these materials, composites, and structures in this paper [1]. One of the main advantages of multifunctional materials is their capacity to simultaneously accomplish multiple functions, which can decrease the need for various materials and components in the system. This benefit can result in reduced weight, higher efficiency, and superior properties and the development of multifunctional materials enables technologies that were previously impossible. The properties of multifunctional materials could vary substantially based on the applications and demands of the material. For example, the materials may respond to heat (thermal), stress &amp; stain (mechanical), electrical, magnetic, pH, moisture, light (photonic), and molecular or biomolecular substances, and others. By incorporating these materials into composites, numerous functionalities, including self-healing, self-sensing, self-cleaning, electric conductive, thermal conductive, membrane, shape memory, and actuation, can be achieved. Therefore, multifunctional materials can improve processes and products, create several avenues to increase sustainability, and have a direct and positive impact on economic growth, environment, and quality of life.

Ultra-stretchable, high-adhesive, self-healable and remoldable hydrogel sensor with dynamic multi-interactions for multiscale motion detection, Braille transmission and temperature monitoring

Flexible wearable electronic sensor has attracted considerable interest due to their inherent advantages, but the multifield and high-precision applications require the development of unique and multifunctional material systems. Herein, carboxymethyl chitosan (CMCS)/sodium alginate (SA)/zwitterionic copolymer (SHA)/4-formylphenylboronic acid (Bn) ionic conductive hydrogel (CSSB) was designed and fabricated by a facile one-pot blending strategy with CMCS and SA as the gel matrix, SAH as the conductive filler and Bn as the dynamic crosslinker. CSSB ionic hydrogel exhibits outstanding mechanical, self-healing, remodeling and electrochemical properties (ultra-high stretchability of 23600%, fracture toughness of 7.01 MJ m−3, 96.6% strain self-healing efficiency at 30 °C for 15 min and electrical conductivity of 3.656 S/m) to satisfy the requirements of various application scenarios. The flexible wearable sensor based on the CSSB ionic hydrogel is demonstrated, and the excellent strain sensing properties endow the sensor to monitor multiscale human movements and to transmit Braille information. Moreover, the sensor can be designed as a temperature sensor with unique thermal sensitivity (-4.48%/°C), outstanding detection accuracy (R2 = 0.9988) and an extremely low detection limit (0.1 °C) for monitoring changes in human body temperature and variations in storage temperature during long distance transport. This work is expected to provide ideas for the next generation of environmental multi-sensory electronic skin and temperature detection electronics.

Liquid metal-hydrogel composites for flexible electronics.

As an emerging functional material, liquid metal-hydrogel composites exhibit excellent biosafety, high electrical conductivity, tunable mechanical properties and good adhesion, thus providing a unique platform for a wide range of flexible electronics applications such as wearable devices, medical devices, actuators, and energy conversion devices. Through different composite methods, liquid metals can be integrated into hydrogel matrices to form multifunctional composite material systems, which further expands the application range of hydrogels. In this paper, we provide a brief overview of the two materials: hydrogels and liquid metals, and discuss the synthesis method of liquid metal-hydrogel composites, focusing on the improvement of the performance of hydrogel materials by liquid metals. In addition, we summarize the research progress of liquid metal-hydrogel composites in the field of flexible electronics, pointing out the current challenges and future prospects of this material.

Microenvironmental Behaviour of Nanotheranostic Systems for Controlled Oxidative Stress and Cancer Treatment.

The development of smart, efficient and multifunctional material systems for diseases treatment are imperative to meet current and future health challenges. Nanomaterials with theranostic properties have offered a cost effective and efficient solution for disease treatment, particularly, metal/oxide based nanotheranostic systems already offering therapeutic and imaging capabilities for cancer treatment. Nanoparticles can selectively generate/scavenge ROS through intrinsic or external stimuli to augment/diminish oxidative stress. An efficient treatment requires higher oxidative stress/toxicity in malignant disease, with a minimal level in surrounding normal cells. The size, shape and surface properties of nanoparticles are critical parameters for achieving a theranostic function in the microenvironment. In the last decade, different strategies for the synthesis of biocompatible theranostic nanostructures have been introduced. The exhibition of therapeutics properties such as selective reactive oxygen species (ROS) scavenging, hyperthermia, antibacterial, antiviral, and imaging capabilities such as MRI, CT and fluorescence activity have been reported in a variety of developed nanosystems to combat cancer, neurodegenerative and emerging infectious diseases. In this review article, theranostic in vitro behaviour in relation to the size, shape and synthesis methods of widely researched and developed nanosystems (Au, Ag, MnOx, iron oxide, maghemite quantum flakes, La2O3−x, TaOx, cerium nanodots, ITO, MgO1−x) are presented. In particular, ROS-based properties of the nanostructures in the microenvironment for cancer therapy are discussed. The provided overview of the biological behaviour of reported metal-based nanostructures will help to conceptualise novel designs and synthesis strategies for the development of advanced nanotheranostic systems.

Asymmetric multi-stability from relaxing the rigid-folding conditions in a stacked Miura-ori cellular solid

Traditionally, origami has been categorized into two groups according to their kinematics design: rigid and non-rigid origami. However, such categorization can be superficial, and rigid origami can obtain new mechanical properties by intentionally relaxing the rigid-folding kinematics. Based on numerical simulations using the bar-hinge approach and experiments, this study examines the multi-stability of a stacked Miura-origami cellular structure with different levels of facet compliance. The simulation and experiment results show that a unit cell in such cellular solid exhibits only two stable states if it follows the rigid origami kinematics; however, two more stable states are reachable if the origami facets become sufficiently compliant. Moreover, the switch between two certain stable states shows an asymmetric energy barrier, meaning that the unit cell follows fundamentally different deformation paths when it extends from one state to another compared to the opposite compression switch. As a result, the reaction force required for extending this unit cell between these two states can be higher than the compression switch. Such asymmetric multi-stability can be fine-tuned by tailoring the underlying origami design, and it can be extended into cellular solids with carefully placed voids. By showing the benefits of exploiting facet compliance, this study could foster multi-functional structures and material systems that traditional rigid origami cannot create.

Preparation and characterization of multifunctional piezoenergetic polyvinylidene fluoride/aluminum nanocomposite films

We prepared poly(vinylidene fluoride) (PVDF) and aluminum composite dense films using a tape caster and investigated the microstructural, thermal, and electrical properties and the combustion behavior of the films as a function of nano-aluminum (nAl) solids loading (5–30 wt. %). We found that the addition of nAl facilitates the formation of piezoelectric β and γ phases of PVDF as determined by x-ray diffraction and Fourier transform infrared spectroscopy. At higher nAl solid loadings, the lower onset temperature of the pre-ignition and decomposition reactions have been observed. Moreover, the intentionally incorporated porosity into the films slightly affected the thermal decomposition behavior. While the dielectric constant of the films increases with higher nAl content, the dielectric breakdown strength of the films decreases significantly. The critical active nAl content for the films to exhibit self-propagated reaction was determined to be between 10 and 15 wt. %. Thermochemical calculations using the NASA CEA code showed the maximum flame temperature of 1750 °C near the stoichiometric ratio (∼20 wt. %). The burning rate of the films is enhanced drastically at ambient conditions with further addition of nAl. However, the films with active nAl content over 20 wt. % showed lower flame temperatures, which is due to the reduction of hydrofluoric acid gas generation and the incomplete combustion of Al to form aluminum monofluoride (AlF), instead of aluminum fluoride (AlF3) gas. The fabrication of energetic thin films with tunable properties could enable their use in multifunctional energetic material systems.

Optimization Design of Ferry Material Performance Test System Based on Artificial Intelligence

Lead titanate in titanium‐titanium mine and lead (solid solution optimized ferroelectric) is one of the most widely used multifunctional material systems, and they are outside the field (such as light, electricity, and heat) Structure, domain, and phase evolution characteristics are important for ferroelectric, piezoelectric, photoelectric, and memory applications. Functional materials are those high‐tech materials with excellent electrical, magnetic, optical, and thermal functions, special physical, and chemical and biological effects, capable of completing functional interconversion, mainly used to manufacture various functional components and are widely used in various high‐tech fields. This paper mainly analyzes iron and electrical materials and artificial intelligence technology by studying the characteristics of ferroelectric materials and research status at home and abroad and using artificial intelligence technology and the calculation of ferroelectric materials for artificial intelligence technology and Dexie optimization model. Artificial intelligence is a new technical science that studies and develops theories, methods, technologies, and application systems for simulating, extending, and expanding human intelligence. For artificial intelligence before the optimization of the hardware and software of the ferroelectric material performance test system, the optimized system is performed; the optimized system is subjected to safety testing; all test results show that the performance test of the ferroelectric material after optimization. The system data is well operating, and the artificial intelligence technology is suitable for optimization of the performance test system of ferroelectric material.

Tunable Magnetism and Insulator–Metal Transition in Bilayer Perovskites

Two-dimensional (2D) transition-metal oxide perovskites greatly expand the field of available 2D multifunctional material systems. Here, based on density functional theory calculations, we predicted the presence of ferromagnetism orders accompanying with an insulator-metal phase transition in bilayer $KNbO_{3}$ and $KTaO_{3}$ by applying strain engineering and/or external electric field. Our results will contribute to the applications of few-layer transition metal oxide perovskites in the emerging spintronics and straintronics.

1-Naphthols as components for multifunctional material systems (MFMS): the molecular modeling approach

Increasing research interests have been paid to developing efficient multifunctional material systems (MFMS) by using various composite materials, owing to their useful properties and good stability. Here, we systematically studied 1-naphthols, especially how the type and position of a substituent influence the reactivity and properties, using different electron-directing groups. During computations, important preparation guidelines for thiol derivatives of 1-naphthol were obtained. It is very interesting to note that some molecules could exhibit intramolecular O–H–O interactions. Careful theoretical investigation reveals that all the tested compounds are stable and the molecules with substituents in positions 4 and 8 are the least reactive. It is also worth noting that for the stability and polarizability tensor values, it is more favorable when both substituents are in the same benzene ring. Among tested 1-naphthols, the greatest values of alpha, beta, and gamma are more than 5, 60, and 110 times better respectively, than in the urea molecule; the change of electron-withdrawing group (EWG) to electron-donating group (EDG) increases NLO effects. This study provided a new scope of 1-naphthols applicability by using them as anti-corrosion materials and as very good materials for NLO devices due to the high stability of the aromatic structure coupled with polarity given by the substituents. Also, the understanding of IR vibrations for more complex organic compounds with thiol substituent has been improved.

Multifunctional smart electronic skin fabricated from two-dimensional like polymer film

Smart skin-like electronics are urgently crucial for artificial muscles, while the development of self-powered two-dimensional-like multifunctional material systems remains significant challenges. Here, we demonstrate a new class of printed smart electronic skin (SES) with multi-sensing properties and energy conversion capability using simple and cost-effective printing techniques. The resulting all-organic self-powering SES functioning as a human-monitoring device where it can detect a variety of external stimuli and works as an ultra-flexible biomechanical energy harvester. Remarkably, our SES exhibits excellent antibacterial properties in addition to self-adaptive performance under various conditions, such as being bent, cut, sewed, hammered, punctured, and washed. The proposed SES devices here have the promise for broad applications in future functional-wearables for human-machine interface, soft robotics, and skin prosthetics.

(Invited) Multi-Functional Flexible Sensor Sheets

Flexible and stretchable electronics are now widely studied for a next class of electric devices replaced from the silicon-based conventional inflexible devices. In particular, multi-functional e-skins can contribute to the applications for wearable healthcare devices and Internet of Things (IoT) concepts. For healthcare application, chemical information such as pH, glucose, sodium ion, and potassium ion levels are very important to monitor as well as physical information including activity, temperature, heartbeat, and electrocardiogram (ECG) signals. Furthermore, simultaneous multiple condition monitoring of physical and chemical information is a next class of wearable devices for convenient and safe human life. To realize the multi-functional flexible sensor system platforms, in this talk, flexible physical and chemical sensor sheets using mainly inorganic nanomaterials will be discussed by proposing low-cost, macroscale, and multi-functional material systems. Especially, human-interactive flexible sensors to detect human motion and health conditions are mainly introduced. After understanding the fundamental properties and mechanism of the flexible sensors such as a strain sensor, a temperature sensor, an ultraviolet sensor, a tactile pressure sensor, and a chemical sensor, integrated device applications with several sensors on a flexible film are demonstrated as proof-of-concepts for multi-functional e-skins. Although a lot of researches and developments are still required for practical application, these studies may help to open a door for the next step of flexible electronics.

Additive manufacturing for energy storage: Methods, designs and material selection for customizable 3D printed batteries and supercapacitors

Abstract Additive manufacturing and 3D printing in particular have the potential to revolutionize existing fabrication processes, where objects with complex structures and shapes can be built with multifunctional material systems. For electrochemical energy storage devices such as batteries and supercapacitors, 3D printing methods allows alternative form factors to be conceived based on the end use application need in mind at the design stage. Additively manufactured energy storage devices require active materials and composites that are printable, and this is influenced by performance requirements and the basic electrochemistry. The interplay between electrochemical response, stability, material type, object complexity and end use application are key to realising 3D printing for electrochemical energy storage. Here, we summarise recent advances and highlight the important role of methods, designs and material selection for energy storage devices made by 3D printing, which is general to the majority of methods in use currently.

Performance and prediction of large deformation contractile shape memory alloy knitted actuators

Compliant, large deformation actuating functional fabrics are essential to next-generation wearables, aerospace structures, and medical devices as they excel at traditional mechanical performance metrics while being soft and pliable. Actuating functional fabrics have been implemented from a variety of multifunctional material systems and fabric manufacturing techniques. A specifically intriguing combination of material system and fabric manufacturing technique are contractile shape memory alloy (SMA) knitted actuators, which generate recoverable actuation deformations of up to 50%, provide actuation forces on the magnitude of 1 N–10 N, are biocompatible, and actuate in response to thermal stimuli. However, the prediction of the knitted functional fabric actuator performance is inherently difficult due to the complex geometry of knitted architectures and the nonlinear material behavior of most multifunctional fibers. This paper presents an empirical model of the contractile SMA knitted actuator performance based on the definition of a dimensionless geometric parameter, the knit index (ik). An experimental study of the contractile SMA knitted actuator quasi-static uniaxial thermo-mechanical performance validates the knit index and the wire diameter as the smallest set of performance-predicting geometric parameters. An empirical model is formulated for the prediction of the contractile SMA knitted actuator performance based on geometric inputs (forward design) and the recommendation of geometric parameters that accomplish specific performance metrics (inverse design). The process of describing and predicting the performance with dimensionless geometric parameters is a step to understanding the mechanics of contractile SMA knitted actuators, has merit for the design of other actuating functional fabrics, and propels the creation of novel wearables, medical devices, and aerospace structures with large actuation deformations.

The Halogen Bond: An Emerging Supramolecular Tool in the Design of Functional Mesomorphic Materials.

Owing to their dynamic attributes, non-covalent supramolecular interactions have enabled a new paradigm in the design and fabrication of multifunctional material systems with programmable properties, performances, and reconfigurable traits. Recently, the "halogen bond" has become an enticing supramolecular synthetic tool that displays a plethora of promising and advantageous characteristics. Consequently, this versatile and dynamic non-covalent interaction has been extensively harnessed in various fields such as crystal engineering, self-assembly, materials science, polymer chemistry, biochemistry, medicinal chemistry and nanotechnology. In recent years, halogen bonding has emerged as a tunable supramolecular synthetic tool in the design of functional liquid-crystalline materials with adjustable phases and properties. In this Concept article, the use of halogen bond in the field of stimuli-responsive smart soft materials, that is, liquid crystals is discussed. The design, synthesis and characterization of molecular and macromolecular liquid crystalline materials are described and the modulation of their properties has been emphasized. The power of halogen bonding in offering a large variety of functional liquid crystalline materials from readily accessible mesomorphic and non-mesomorphic complementary building blocks is highlighted. The article concludes with a perspective on the challenges and opportunities in this emerging endeavor towards the realization of enabling and elegant dynamic functional materials.

Structural metals at extremes

Designing structural materials for tailored response at extreme conditions is a grand challenge in materials research. Such materials can be made using either "top-down" or "bottom-up" processes to create nanostructured metals and composites that contain atomically designed interfaces that not only block dislocation slip but also attract, absorb, and annihilate point and line defects. Such multifunctional material systems are not just high in strength but also tolerant of damage at extremes of irradiation, temperature, and mechanical stresses, and hence have applications as structural materials in nuclear power and other energy, transportation, and defense technologies. The exploration of these exceptional properties at extremes requires novel and unconventional methodologies, such as in situ experiments with high spatial and temporal resolution, complemented by simulation across multiple length and time scales.

Ultralow wear of gallium nitride

Here, we reveal a remarkable (and surprising) physical property of GaN: it is extremely wear resistant. In fact, we measured the wear rate of GaN is approaching wear rates reported for diamond. Not only does GaN have an ultralow wear rate but also there are quite a few experimental factors that control the magnitude of its wear rate, further contributing to the rich and complex physics of wear of GaN. Here, we discovered several primary controlling factors that will affect the wear rate of III-Nitride materials: crystallographic orientation, sliding environment, and coating composition (GaN, InN and InGaN). Sliding in the ⟨12¯10⟩ is significantly lower wear than ⟨11¯00⟩. Wear increases by 2 orders of magnitude with increasing humidity (from ∼0% to 50% RH). III-Nitride coatings are promising as multifunctional material systems for device design and sliding wear applications.

Bi-objective optimal design of a damage-tolerant multifunctional battery system

In current electric vehicles (EVs), battery systems only serve the role of electrical energy storage. Heavy protecting structures surround the batteries. To enhance the overall performance of EVs one desires multifunctional battery systems with structural and energy storage functionalities. Our research centers on the design methodology to enable such multifunctional material systems. An architectured multifunctional battery-structure material system, namely the Cellular Battery Assembly (CBA), is introduced. The CBA is composed of cylindrical battery cells surrounded by hollow tubes. The CBA inherits features of the energy absorbing characteristics of periodic cellular materials while maintaining an electrical energy storage. The energy absorbing mechanism is activated when intentional collapse of hollow tubes dissipates energy and protects battery units from high compressive stress. Depending on loading conditions to be applied, the multi-functionalities of CBA can be optimized by morphological or dimensional control of the building blocks through a multi-objective optimization process. The present study focuses on a multi-objective optimization design process to achieve optimal configurations in specific applications where energy storage and energy absorption are objective functions to be maximized simultaneously. Results show that CBA can possess energy absorption performance that compares well to other energy absorbing materials while a desirable energy storage capability is maintained.

Multifunctional Material Systems: A state-of-the-art review

An increase in system-level efficiency and multifunctionality of products and components is one of the main advantages of the use of some novel polyvalent materials and structures. This polyvalence or multifunctionality is currently a hot topic in science and engineering circles and is gathering more and more attention. Presently, this multifunctionality can be achieved by stimuli responsive materials such as temperature, stress and light, by using shape memory materials, by using surface structures with anti-biofouling and drag reduction capabilities, among many others. In this article, an overview of the topic is presented, including state-of-the-art review and future directions to increase innovation in developing both these materials and structures.

Piezoresistive Strain Sensors Based on Carbon Nanotube Networks: Contemporary approaches related to electrical conductivity

Since they were discovered in 1991 [2], CARBON nanotubes (CNTs) have attracted enormous attention because of their remarkable properties [1], such as high electrical conductivity, ultrasmall diameter, and large aspect ratio. In addition, CNTs exhibit significant electromechanical properties [3] that could be useful in applications for piezoresistive-type sensors such as strain gauges, pressure sensors, chemical and biological sensors, microelectronic devices, and structural condition monitoring through strain sensing [4]. In addition to the application of a single CNT in various nanoelectromechanical applications, CNT researchers have gradually moved toward potential applications of CNTs as filler candidates in various types of multifunctional material systems, representing a new direction with broad applications [5], [6].