Porous and Ultra-Flexible Crosslinked MXene/Polyimide Composites for Multifunctional Electromagnetic Interference Shielding

In recent years, the demand for digital transformation (DX) in the industrial sector has been extremely high. In response to this high demand, a variety of smart devices have been invented and offered. Especially in the research field, flexible or bendable smart devices have been devised by using thin-film polymers such as polyimide and parylene as substrates. Micro/nanofabrication is a fundamental technology in the research and development of these smart devices. The presenter's laboratory has conducted research on flexible smart devices for social implementation based on micro/nanofabrication. Based on the knowledge obtained from flexible smart devices, we have also studied stretchable devices, which are expected to be the next generation of smart devices. In this presentation, we report an overview of our research on flexible smart devices and stretchable systems. In particular, we present our research on flexible smart devices and the development of smart devices for use in medical and animal experiments. In addition, research on stretchable sensors using liquid metal and stretchable systems are reported. Stretchable devices based on micro- and nano-fabrication might be further accelerated toward social implementation in the future.

Origami offers two-dimensional (2D) materials with great potential for applications in flexible electronics, sensors, and smart devices. However, the dynamic process, which is crucial to construct origami, is too fast to be characterized by using state-of-the-art experimental techniques. Here, to understand the dynamics and kinetics at the atomic level, we explore the edge effects, structural and energy evolution during the origami process of an elliptical graphene nano-island (GNI) on a highly ordered pyrolytic graphite (HOPG) substrate by employing steered molecular dynamics simulations. The results reveal that a sharper armchair edge is much easier to be lifted up and realize origami than a blunt zigzag edge. The potential energy of the GNI increases at the lifting-up stage, reaches the maximum at the beginning of the bending stage, decreases with the formation of van der Waals overlap, and finally reaches an energy minimum at a half-folded configuration. The unfolding barriers of elliptical GNIs with different lengths of major axis show that the major axis should be larger than 242 Å to achieve a stable single-folded structure at room temperature. These findings pave the way for pursuing other 2D material origami and preparing origami-based nanodevices.

Transparent electrodes (TEs) are crucial in a wide range of modern electronic and optoelectronic devices. However, traditional TEs cannot meet the requirements of smart devices under development in unique fields, such as electronic skins, wearable electronics, robotic skins, flexible and stretchable displays, and solar cells. Emerging TEs printed with nanocrystal (NC) inks are inexpensive and compatible with solution processes, and have huge potential in flexible, stretchable, and wearable devices. Every development in ink-based electrodes makes them more competitive for practical applications in various smart devices. Herein, we provide an overview of emergent ink-based electrodes, such as transparent conducting oxides, metal nanowires, graphene, and carbon nanotubes, and their application in solution-based flexible and stretchable devices.

With the rapid development of 5G communication technologies, the high-performance electromagnetic interference (EMI) shielding materials with less secondary reflection for electronic devices have become an urgent demand in recent years. In this study, flexible open-cell polyimide (PI) foams containing graphene nanoplatelets (GN)/Fe3O4 coatings for absorption-dominated EMI shielding were fabricated. The result shows that the EMI shielding efficient (EMI SE) of composite foam PI/GN/Fe3O4 (PF/GN/Fe3O4) can achieve 60.6 dB with a thickness of 6.0 mm along with an absorption coefficient (A) of 0.4–0.6, indicating excellent EMI shielding and a low reflection property. Furthermore, the optimal reflection loss (RL) of PF/GN/Fe3O4 with a low GN loading can be up to −35 dB at 5.0 mm and less than or equal to −10 dB in the whole X-band with a thickness of ≥4.5 mm. In addition, the prepared composite foam PI/GN (PF/GN) exhibits good electrical conductivity of 2.5 × 103 S/m and sensing stability. Notably, this research systematically studied the application performance of the composite foam in EMI shielding, electromagnetic wave (EW) absorption, and sensing monitoring. The prepared composite foam can be applied as “Green” EMI shielding materials for flexible electronic devices due to the remarkable EW absorption properties.

With the rapid development of wearable devices, flexible sensors, and flexible displays, higher performance requirements are being placed on conductive materials used in flexible electronic devices. Conductive polymers, known for their excellent flexibility, good conductivity, and tunable molecular structures, have become a research hotspot in the field of flexible electronics. This paper systematically summarizes the design and synthesis strategies of conductive polymers for flexible electronic devices, with a focus on the synthesis methods and structural regulation techniques of typical conductive polymers such as polyaniline (PANI), polypyrrole (PPy), and poly(3,4-ethylenedioxythiophene) (PEDOT). It further analyzes their electrical properties, mechanical performance, and environmental stability in flexible electronics. Finally, the paper discusses future development trends and challenges of conductive polymers in flexible devices, aiming to provide a theoretical foundation and technical support for the research of high-performance flexible electronic materials.

There is growing attention and rapid development on flexible electronic devices with electronic materials and sensing technology innovations. In particular, strain sensors with high elasticity and stretchability are needed for several potential applications including human entertainment technology, human–machine interface, personal healthcare, and sports performance monitoring, etc. Significant advancements in wearable and flexible electronic and photonic technologies, are materials science of new and alternative materials and methods of coating and deposition, characterization of flexible and transparent or display electronic devices, the electronics behind new sensor development for wearables and flexible technology, and new device design concepts.The anisotropic properties of a system comprising a guest dye dissolved in an aligned liquid-crystalline host were reported, arising from the combination of the bulk liquid crystal host alignment and the anisotropic shape and absorption characteristics of the dye molecules. For many applications, it is also desirable for a guest–host mixture to exhibit a long useable lifetime in addition to the optical properties described above. Many of the proposed applications involve exposure of the systems to wearable and flexible device, polarisers, smart windows and lasers. The stability of a dye molecule may be strongly dependent on its chemical environment, so the stabilityof a guest–host system may depend on the nature of the host mixture as well as that of the dye. A series of new fluorescent dichroic dyes which included phenylacetylene substituent group to 4-site of the 1,8-dicyanonaphthene were synthesized. All dyes were characterized by nuclear magnetism and high resolution mass spectrum. The dicyanonaphthene fluorescent dichroic dyes meet the application conditions of ‘Guest-host’ display. Phenylacetylene bridge bond is often used for liquid crystal molecular design and synthesis to improve the liquid crystal birefringence because of its excellence stability, optical anisotropy.On the one hand, the addition of the phenylacetylene bond increases the molecular linearity and the aspect ratio, which is more favorable for the arrangement of the dye molecules in the main liquid crystal, thereby increasing the ordered parameters of the dye molecules in the liquid crystal; On the other hand, phenylacetylene bonds can increase the molecular conjugation system and optimize the optical properties of dye molecules. Ester groups as a class of important linking groups have been widely used in the synthesis of diamodal dyes4.The 1,8-naphthalene dinitrile is regarded as the precursor, introduced p-ethynylbenzoic acid at its 4-position and then through the acylation reaction to introduce the alkoxy chain, in order to obtain a greater degree of conjugation, in the main liquid crystal has good solubility and high dichroic dye. Acknowledgements We are grateful to the National Natural Science Foundation of China (21576043), supported by the Fundamental Research Funds for the Central Universities.

Piezocatalysis is a physical/chemical process that utilizes piezoelectric potential to drive chemical reactions, harnessing ubiquitous mechanical energies from the nature for various catalysis applications. Despite the high efficiency of piezocatalytic powders, the particles tend to disperse in aqueous systems and are difficult to separate, which poses a risk of secondary pollution. Herein, a flexible piezocatalytic foam is designed and fabricated, which is composed of potassium sodium niobate (KNN) piezoelectric powders embedded in the PDMS scaffold. The as-prepared KNN-PDMS composite foam demonstrates excellent piezocatalytic efficiency for organic pollutant removal among state-of-the-art integral piezocatalytic platforms, which lie in the synergy of proper piezoelectric materials and abundant interconnected pores within the flexible foam. In addition, as a monolithic platform, KNN-PDMS foam is easy to be collected, with high recycle stability and applicability for treating various pollutants, resulting in dominant advantages over powder-based systems for practical high-flux wastewater treatment. Significantly, the optimized 1.5KNN-PDMS sample achieved a RhB degradation rate constant of 34.71×10 -3 min -1 , with only a 7.5% decrease in activity after four consecutive cycles, and the KNN-PDMS foam maintained excellent selectivity toward RhB. This work not only mitigates the problem of secondary pollution but also provides a practical and efficient strategy for the stable degradation of organic pollutants in real aqueous environments.

The demand of innovative solutions to afford healthy and safe lifestyle, for elderly people, are increasing lead by the growth of the ageing population and age-related diseases. Moreover, the availability of smart devices based on IoT technologies for personal environments has evolved the demand for tools to monitor and remotely control the home equipment. A new generation of remote control is available: Electronic Personal Assistants. These devices could be controlled using natural user interfaces, help user to simplify the interaction with home automation and other smart devices. The personal assistants use machine learning strategies to interact with the user. The solutions available in the market are often expensive and, moreover, are limited and legacy since based on proprietary hardware and software. This paper aims to present Alfred, a flexible and modular smart personal assistant based on low-cost hardware and open source machine learning software, in the context of the City4Age, an H2020 Project, to provide Elderly-friendly ambient assisted living.

Exciting advancements have been made in the field of flexible electronic devices in the last two decades and will certainly lead to a revolution in peoples' lives in the future. However, because of the poor sustainability of the active materials in complex stress environments, new requirements have been adopted for the construction of flexible devices. Thus, hierarchical architectures in natural materials, which have developed various environment-adapted structures and materials through natural selection, can serve as guides to solve the limitations of materials and engineering techniques. This review covers the smart designs of structural materials inspired by natural materials and their utility in the construction of flexible devices. First, we summarize structural materials that accommodate mechanical deformations, which is the fundamental requirement for flexible devices to work properly in complex environments. Second, we discuss the functionalities of flexible devices induced by nature-inspired structural materials, including mechanical sensing, energy harvesting, physically interacting, and so on. Finally, we provide a perspective on newly developed structural materials and their potential applications in future flexible devices, as well as frontier strategies for biomimetic functions. These analyses and summaries are valuable for a systematic understanding of structural materials in electronic devices and will serve as inspirations for smart designs in flexible electronics.

Recent advances in smart polymers have taken the fabrication of high-performance flexible and stretchable devices to the next level. The rigid materials for various device components are now being replaced by flexible smart polymers. The fact that the smart polymers respond to the ex situ environment by altering their structures and properties makes them promising materials for making electronic devices. These smart polymers are capable of responding to the changes in physical parameters and can change their physical and chemical properties reversibly. To maintain stability, they can either swell or collapse or covert gel-to-solution and vice versa based on their chemical nature. Different kinds of smart polymers are envisaged, such as pH-sensitive, temperature-sensitive, photo-sensitive and photo-resistive, conductive polymers, hydrogels, anti-inflammatory, shape-memory, self-healing, etc. This chapter gives detailed information on these different types of smart polymers and their fabrication approaches. Furthermore, these polymers have shown great potential in flexible electronic devices for medical diagnosis, biosensors, actuators, lab-on-chip, microfluidic devices, drug delivery, electrochemical sensors, and energy devices like supercapacitors, fuel cells batteries, etc. This chapter also gives an overview of these applications. Further, the chapter discusses the future scope of these polymers.

In recent years, the field of electronics has witnessed a revolutionary transformation with the emergence of nanoelectronics and related technologies. This abstract delves into the realm of Nanoscale electronic devices and applications, Quantum electronics and quantum computing, Organic and flexible electronics, the smart devices and Internet of Things (IoT). Nanoscale electronic devices have paved the way for groundbreaking advancements in various domains. As electronic components continue to shrink to nanoscale dimensions, novel materials and structures are being explored to enhance device performance. Nanoscale transistors, such as carbon nanotubes and nanowires, have shown the potential to overcome the limitations of conventional silicon transistors in terms of power consumption and switching speed, unlocking new possibilities in electronics and computing. These nanoscale components have the potential to lead to faster, more energy-efficient devices with applications ranging from portable gadgets to high-performance computing systems. Quantum electronics represents the next frontier in electronics research, where quantum effects are harnessed to develop transformative technologies. Quantum computing, in particular, has garnered immense interest due to its potential to revolutionize computation. Quantum computers leverage quantum bits or qubits, which can exist in multiple states simultaneously. It also allow them to perform certain computations exponentially faster than classical computers. Quantum algorithms have the potential to tackle complex problems in cryptography, optimization, and materials science, pushing the boundaries of what is currently achievable in traditional computing paradigms. Organic and flexible electronics have opened up new avenues for seamless integration of electronics into various products and applications. Organic materials, such as organic semiconductors and conductive polymers, offer the advantage of low-cost processing and the ability to be printed on flexible substrates. This allows for the creation of flexible displays, wearable electronics, and even electronic skins that can sense and interact with their surroundings. Organic and flexible electronics are enabling the development of lightweight and conformable devices with applications in healthcare, consumer electronics, and the Internet of Things (IoT). Speaking of the IoT, the interconnectivity of smart devices has become a transformative force in modern life. The IoTdeals with a vast network of devices, sensors, and actuators that communicate with each other and also with the cloud, collecting and exchanging data to enable intelligent decision-making and automation. Nanoscale electronic devices play a crucial role in the IoT ecosystem, as miniaturized sensors and low-power processors are essential for creating smart, energy-efficient devices. The IoT has applications in various sectors, including smart homes, healthcare, agriculture, transportation, and industrial automation. This abstract highlights the exciting prospects brought forth by Nanoelectronics and Emerging Technologies, including nanoscale electronic devices and applications, quantum electronics and quantum computing, organic and flexible electronics, and the IoT and smart devices. As these technologies continue to evolve, they are expected to reshape industries, enhance our quality of life, and drive further innovation in the electronics domain. However, it is crucial to address the challenges posed by these emerging technologies, such as security and privacy concerns, ethical considerations, and environmental impacts, to ensure that they are deployed responsibly and sustainably in our increasingly interconnected world.

Marangoni-flow-assisted assembly of single-walled carbon nanotube films for human motion sensing

In recent years, flexible electronic devices have become a hot topic of scientific research. These flexible devices are the basis of flexible circuits, flexible batteries, flexible displays and electronic skins. Graphene-based materials are very promising for flexible electronic devices, due to their high mobility, high elasticity, a tunable band gap, quantum electronic transport and high mechanical strength. In this article, we review the recent progress of the fabrication process and the applications of graphene-based electronic devices, including thermal acoustic devices, thermal rectifiers, graphene-based nanogenerators, pressure sensors and graphene-based light-emitting diodes. In summary, although there are still a lot of challenges needing to be solved, graphene-based materials are very promising for various flexible device applications in the future.

Flexible electrochromic technology has gained numerous attentions in flexible smart wearable devices and flexible displays. For large-area flexible electrochromic devices (FECDs), highly conductive transparent electrodes with advanced stability at a prolonged redox cycling process are indispensable. In this work, a silver (Ag)/nickel (Ni) mesh/PH 1000 hybrid transparent film were successfully fabricated by selectively electrodepositing an 800 nm-thick dense metallic Ni layer and coating PH 1000 on an embedded Ag mesh to improve its electrochemical stability. The prepared hybrid transparent film presented high conductivity with a sheet resistance of below 1.5 Ω sq−1 at over 80% optical transmittance. The Ag/Ni mesh/PH 1000 was successfully utilized as current collectors for all-solid-state FECDs, showing fast coloration switching with a bleaching/coloring time of 0.7 s/0.9 s. In addition, the device demonstrated an exceptional electrochemical cycling stability, which could sustain 89% of its initial optical modulation after 25 000 cycles. More importantly, a remarkable mechanical durability was also achieved with a small optical modulation decay of 15% and an invariable response time after 1000 rolling cycles. In addition, uniform coloration were realized on a 6 × 6 cm2 FECD, demonstrating its great potential for applications of next-generation up-scaling FECDs.

From flexible electronics to flexible photonics: A brief overview