A review of recent progress in multi-component organic thermochromic materials: mechanisms, performance optimization, and applications

Multicomponent materials are microwave-absorbing (MA) materials composed of a variety of absorbents that are capable of reaching the property inaccessible for a single component. Discovering mostly valuable properties, however, often relies on semi-experience, as conventional multicomponent MA materials' design rules alone often fail in high-dimensional design spaces. Therefore, we propose performance optimization engineering to accelerate the design of multicomponent MA materials with desired performance in a practically infinite design space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with the expanded Maxwell-Garnett model, electromagnetic calculations, and experimental feedback; aiming at different desired performances, Ni surface@carbon fiber (NiF) materials and NiF-based multicomponent (NMC) materials with target MA performance were screened and identified out of nearly infinite possible designs. The designed NiF and NMC fulfilled the requirements for the X- and Ku-bands at thicknesses of only 2.0 and 1.78 mm, respectively. In addition, the targets regarding S, C, and all bands (2.0-18.0 GHz) were also achieved as expected. This performance optimization engineering opens up a unique and effective way to design microwave-absorbing materials for practical application.

Organic Thermoelectrics: Materials Preparation, Performance Optimization, and Device Integration

Organic thermoelectric materials have the potential to be used as power supplies for wearable electronics, implantable medical devices, and sensors in Internet of Things. The past 10 years has witnessed the rapid development of the research on organic thermoelectric materials, different material systems and optimizing strategies are developed, and the ZT values of some organic materials have approached that of many inorganic thermoelectric material systems in the low‐temperature region. Among different material systems, organic composite materials, especially multicomponent organic composite materials show very promising thermoelectric properties and offer more tunability compared to single component thermoelectric materials. Multicomponent organic composite thermoelectric materials can not only further improve the ZT values, but also have unique advantages of combining the merits of different materials, thus rendering the composites with better processing, mechanical, or other properties on demand. This review summarizes the concepts, the design criteria, the research progress of organic–inorganic and all‐organic multicomponent thermoelectric materials which contain three or more different ingredients, as well as their applications. Furthermore, the challenges and prospects are also analyzed to provide guidelines for the development of multicomponent organic composite thermoelectric materials.

Body Heat Powers Future Electronic Skins

Na-ion batteries (NIBs) are promising alternatives to Li-ion batteries (LIBs) due to the low cost, abundance, and high sustainability of sodium resources. However, the high performance of inorganic electrode materials in LIBs does not extend to NIBs because of larger ion size of Na+ than Li+ and more complicated electrochemistry. Therefore, it is vital to search for high-performance electrode materials for NIBs. To this end, organic electrode materials (OEMs) with the advantages of high structural tunability and abundant structural diversity show great promise in developing high-performance NIBs. To achieve advanced OEMs for NIBs, a fundamental understanding of the structure–performance correlation is desired for rational structure design and performance optimization. Tailoring molecular structures of OEMs can enhance their performance in Na-ion batteries, however, the substitution rules and the consequent effect on the specific capacity and working potential remain elusive. Herein, we explored the electrochemical performances and reaction mechanisms of various carboxylate-based anode materials, including halogenated sodium carboxylates, N-doped sodium carboxylates, etc. By examining sodium carboxylates with different functional groups, selective N substitution, and extended conjugation structure, we exploited the correlation between structure and performance to establish substitution rules for high-capacity OEMs. Our results show that substitution position and types of functional groups are essential to create active centers for uptake/removal of Na+ and thermodynamically stabilize organic structures. Furthermore, rational host design and electrolytes modulation were performed to extend the cycle life. In addition to sodium carboxylate-based anode materials, we also designed and synthesized novel organic cathode materials based on azo and carbonyl groups for NIBs. The electrochemical performance of the organic cathode materials with an extended conjugated structure such as a naphthalene backbone structure is better than that with benzene and biphenyl structures due to faster kinetics and lower solubility in the electrolyte. It unravels the rational design principle of extending π-conjugation aromatic structures in redox-active polymers to enhance the electrochemical performance. To further optimize the organic cathodes, nitrogen-doped or single layer graphene is employed to increase the conductivity and mitigate the dissolution of organic materials in the electrolytes. The resulting organic cathodes deliver high specific capacity, long cycle life, and fast-charging capability. Post-cycling characterizations were employed to study the chemical structure and morphology evolution upon cycling, demonstrating that the active centers (azo and carbonyl groups) in the organic cathode materials can undergo reversible redox reactions with Na+ for sustainable NIBs. Our work provides a valuable guideline for the design principle of high-capacity and stable OEMs for sustainable energy storage.

Tailoring π-Conjugated Systems: From π-π Stacking to High-Rate-Performance Organic Cathodes

Pentacene is widely used in organic transistors as an organic semiconductor material. The conductivity of pentacene is enhanced in recent days, which helps in improving the device characteristics of organic transistors providing additional benefit of low-cost and flexible devices. Modeling and simulation of such devices are constructive in analyzing device characteristics. Here, in this paper modeling and simulation of four different configurations of organic transistor – two on the basis of the bottom gate and two on the basis of the top gate – is done in order to analyze the transfer and output characteristics. Off current of 10-15 A, and low subthreshold swing of 0.347 V/decade was observed.

Range-separated hybrid (RSH) functionals have become a tool of choice to study the intra- and inter-molecular electronic states in organic materials. These functionals provide the most accurate descriptions of the electronic structure when the range-separation parameter is optimally tuned (OT). However, since the range-separation parameter is molecule dependent, this approach faces consistency issues when applied to the multicomponent systems typically found in the active layers of organic solar cells or organic light-emitting diodes (OLEDs). Here, we investigate the performance of four common RSH functionals in the description of the excited states of three molecular compounds used as components of the active layer in a hyperfluorescence OLED device. Our results indicate that the excited-state energies of the investigated molecules show a very weak dependence on the range-separation parameter value when they are evaluated by means of a screened version of RSH functionals. In this instance, the excited states of all three molecular compounds can be derived accurately and consistently with the exact same functional.

Developing an atomistic understanding of ionizing radiation induced changes to organic materials is necessary for intentional design of greener and more sustainable materials for radiation shielding and detection. Cocrystals are promising for these purposes, but a detailed understanding of how the specific intermolecular interactions within the lattice upon exposure to radiation affect the structural stability of the organic crystalline material is unknown. This study evaluates atomistic-level effects of γ radiation on both single- and multicomponent organic crystalline materials and how specific noncovalent interactions and packing within the crystalline lattice enhance structural stability. Dose studies were performed on all crystalline systems and evaluated via experimental and computational methods. Changes in crystallinity were evaluated by p-XRD and free radical formation was analyzed via EPR spectroscopy. Type of intermolecular interactions and packing within the crystal lattice was delineated and related to the specific free radical species formed and the structural integrity of each material. Periodic DFT and HOMO-LUMO surface mapping calculations provided atomistic-level identifications of the most probable sites for the radicals formed upon exposure to γ radiation and relate intermolecular interactions and molecular packing within the crystalline lattice to experimental results.

A method for determining the content of one element in the multi-component samples is proposed. In the known methods of X-ray fluorescent analysis, the standard composition samples are used, or the fundamental parameters method is applied to determine the intensity of the analytical line of the defined element from the content in order to account for the inter-nutrient influences. A distinctive feature of the method in determining the content of one element in the material proposed by the current study does not require the use of standard samples and does not require the measurements of other elements that are part of the sample being analyzed to account for the inter-nutrient influences. This approach is most convenient and economical when it comes to determining the content of one or more elements in the multi-component materials on the simple single-channel X-ray spectrometers and analyzers. The possibility of implementing such solution is based on using the measured intensity of the analytical line of the defined element in the single-element sample and in the material under study and calculating the content of the defined element with the record absorption factor of the - the relationship of absorbent properties of filler to the absorption properties of the defined element. The calculation of the absorption factor is carried out using a program to compute the theoretical intensity considering all the influencing factors. Experimental testing of the proposed method was performed using the standard samples of steel and brass composition. A theoretical assessment of the effectiveness of the method in determining niobium in zirconium as well as harmful impurities in organic materials has been conducted. Keywords : X-ray fluorescent analysis, definition of one element, multi-component samples, steel and alloys, organic materials, absorption factor (Russian) DOI: http://dx.doi.org/10.15826/analitika.2019.23.4.006 B.D. Kalinin “Pretsizion Tekhnologies” Co. Lt, u l. Altai, 12, St. Petersburg, 196066, Russian Federation

Due to the ever-increasing energy consumption and environmental pollution by the fossil fuel-based motor vehicles, the development and application of electric vehicles attract considerable research interests from academia and industry. A key challenge for the state-of-the-art electric vehicles is the slow charge rate, which requires several hours to fully recharge the batteries in electric vehicles. Further increasing the charge rate for electric vehicle can reduce the recharge time, but it results in the failure of batteries in electric vehicles because of the limited electron/ion conductivity and slow electrochemical reaction rate of the battery materials. Therefore, exploiting new battery materials and electrode structures becomes a critical and urgent task for the development of electric vehicles. Organic materials and polymers with the advantages of low cost, abundance, high sustainability and high structural tunability are promising electrode materials for fast-charging batteries. Several novel conjugated organic materials and porous polymers based on azo group, imine group and carbonyl group are designed and synthesized for alkali-ion batteries. These multifunctional organic electrode materials demonstrate exceptional electrochemical performance in terms of long cycle life and fast-charging capability. High specific capacity and long cycle life have been achieved at both low and high current densities. At the high current density of up to 25C and 10 A/g, these new materials can still retain a reversible capacity above 100 mA/g for thousands of cycles in Li-ion and Na-ion batteries, representing one of the best performances in rechargeable batteries. To gain fundamental insights into the reaction mechanisms and fast kinetics of these new materials, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT) are used to study the interaction between functional groups (C=O/C=N/N=N) and cations (Li+/Na+), as well as ion diffusivity and interfacial impedance. The results indicate that the fast-charging capability of multifunctional organic electrode materials is attributed to the extended conjugation structure, large surface area and high porosity. Developing conjugated and porous structures is critical for the fast reaction kinetics of organic electrode materials. Therefore, our study provides guidance for the rational structure design and performance optimization for sustainable and fast-charging organic batteries.

High throughput approaches to designer products—myth or reality

With the rapid development of smart electronics, intrinsically stretchable organic electronic materials with excellent electrical properties have exhibited huge application potential in wearable electronics and artificial intelligent fields. Mechanical stretchability and electrical property often tend to interfere with each other, which impedes the development and usage of stretchable organic electronic materials. To meet various practical applications, it is quite vital for intrinsically stretchable organic electronic materials to obtain synergistic mechanical and electrical properties through reasonable materials design and structure optimization. In this chapter, we systematically analyse and summarize the recent research progress of intrinsically stretchable organic conducting materials, including representative organic conducting materials, structure design and performance optimization, practical and potential application. Finally, the future development directions, possible challenges and opportunities of intrinsically stretchable organic conducting materials are discussed and proposed.

While multicomponent microand nanoscale structures and even atomically blended materials have been in use for centuries in various bulk forms ranging from metal-nanoparticle-doped glasses to crystalline alloys, recent advances in top-down and bottom-up fabrication processes have allowed for improved control over the structure of microand nanoscale multicomponent materials. These multicomponent microstructured materials are important in imaging, drug delivery, sensing, and tissue engineering. A simple example of such a material is the core–shell particle, where the shell could improve the compatibility with the surrounding environment in imaging applications, provide for a controlled release profile in drug delivery, or give tuneable absorption properties in plasmonic particles. While the core–shell configuration has its utility, there is ample room for more complex configurations. In drug delivery and diagnostics, for example, it would be attractive to have a platform where multiple compartments of a microstructured material could be used to: 1) target the desired cells, 2) deliver the desired drug(s) at the desired rate(s) for the required duration(s), and 3) label the treated cells for diagnostic evaluation. Various techniques have been utilized to fabricate multicomponent microstructured materials with core–shell, nested, Janus, and/or granular architecture. Figure 1 depicts examples of multiphase microstructures patterned by various techniques, including the microfluidic sheath flow of granular Janus particles (Figure 1a), laser direct writing of a trapped colloidal fluid (Figure 1b), electrospinning of inorganic– organic hybrid materials in core–sheath and side-by-side configurations (Figure 1c and d), and the electrospray and cellular uptake of water-stable Janus particles (Figure 1e). While the solution-phase syntheses of particles can be scaled up readily, they have not been well suited for the arbitrary placement of multiple components on the microscale. Stan-

Cement based composites i.e. paste, mortar and concrete are the most utilized materials in the construction industry all over the world. Cement composites are quasi-brittle in nature and possess extremely low tensile strength as compared to their compressive strength. Due to their low tensile strength capacity, cracks develop in cementitious composites due to the drying shrinkage, plastic settlements and/or stress concentrations (due to external restrains and/or applied stresses) etc. These cracks developed at the nanoscale may grow rapidly due to the applied stresses and join together to form micro and macro cracks. The growth of cracks from nanoscale to micro and macro scale is very rapid and may lead to sudden failure of the cement composites. Therefore, it is necessary to develop such types of cement composites possessing higher resistance to crack growth, enhanced flexural strength and ductility. The development of new technologies and materials has revolutionized every field of science by opening new horizons in production and manufacturing. In construction materials, especially in cement and concrete composites, the use of nano/micro particles and fibers in the mix design of these composites has opened new ways from improved mechanical properties to enhanced functionalities. Generally, the production or manufacturing processes of the nano/micro sized particles and fibers are energy intensive and expensive. Therefore, it is very important to explore new methods and procedures to develop less energy intensive, low cost and eco-friendly inert nano/micro sized particles for utilization in the cement composites to obtain better performance in terms of strength and ductility. The main theme of the present research work was to develop a family of new type of cementitious composites possessing superior performance characteristics in terms of strength, ductility, fracture energy and crack growth pattern by incorporating micro sized inert carbonized particles in the mix design of cementitious composites. To achieve these objectives the micro sized inert carbonized particles were prepared from organic waste materials, namely: Bamboo, coconut shell and hemp hurds. For comparison purposes and performance optimization needs, another inorganic waste material named as carbon soot was also investigated in the present research. The experimental investigations for the present study was carried out in two phases; In the first phase of research work, a methodology was developed for the synthesis of the micro sized inert carbonized particles from the above mentioned organic raw materials. In the second phase of research, various mix proportions of the cementitious composites were prepared incorporating the synthesized micro sized inert carbonized particles. For micro sized inert carbonized particles obtained from bamboo and coconut shell three wt.% additions i.e. 0.05, 0.08, 0.20 were investigated and for particles synthesized from hemp hurds 0.08, 0.20, 1.00 and 3.00 wt.% additions were explored. The cement composites were characterized by third-point bending tests and their fracture parameters were evaluated. The mechanical characterization of specimens suggested that 0.08 wt.% addition of micro sized inert carbonized bamboo particles enhances the flexural strength and toughness of cement composites up to 66% and 103% respectively. The toughness indices I5, I10 and total toughness of the cement composites were also enhanced. The carbonized particles synthesized from coconut shell resulted in improved toughness and ductility without any increase in the modulus of rupture of the cement composite specimens. Maximum enhancements in I5 and I10 were observed for 0.08% addition of both carbonized and carbonized-annealed particles. For the carbonized hemp hurds cement composites the results indicate that the micro sized inert carbonized particles additions enhanced the flexural strength, compressive strength and the fracture energy of the cement composites. The microstructure of the cement composites was also studied with the help of field emission scanning electron microscope (FESEM) by observing small chunks of cement composite paste samples. The FESEM observations indicated that the micro sized inert carbonized particles utilized in the mix design of these mixes were well dispersed in the cement matrix. It was also observed that the fracture paths followed by the cracks were tortures and irregular due the presence of micro particles in the matrix. The cracks during their growth often contoured around the inert particle inclusions and resulted in enhanced energy absorption capacity of the cement composites. The study was further enhanced to the cement mortar composites and their performances were studied. The results indicated that the energy absorption behavior of the composites was enhanced for all the cement composites containing micro carbonized particles. Finally, it is concluded that the ductility and toughness properties of the cement composites can be enhanced by incorporating the micro sized inert carbonized particles in the cement matrix. The fracture energy, ductility and toughness properties enhancement of the cement composites greatly depends upon the source and synthesis procedure followed for the production of micro sized inert carbonized particles