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Abstract Thermoelectric textile devices represent an intriguing avenue for powering wearable electronics. The lack of air‐stable n‐type polymers has, until now, prevented the development of n‐type multifilament yarns, which are needed for textile manufacturing. Here, the thermomechanical properties of the recently reported n‐type polymer poly(benzodifurandione) (PBFDO) are explored and its suitability as a yarn coating material is assessed. The outstanding robustness of the polymer facilitates the coating of silk yarn that, as a result, displays an effective bulk conductivity of 13 S cm−1, with a projected half‐life of 3.2 ± 0.7 years at ambient conditions. Moreover, the n‐type PBFDO coated silk yarn with a Young's modulus of E = 0.6 GPa and a strain at break of εbreak = 14% can be machine washed, with only a threefold decrease in conductivity after seven washing cycles. PBFDO and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) coated silk yarns are used to fabricate two out‐of‐plane thermoelectric textile devices: a thermoelectric button and a larger thermopile with 16 legs. Excellent air stability is paired with an open‐circuit voltage of 17 mV and a maximum output power of 0.67 µW for a temperature difference of 70 K. Evidently, PBFDO coated multifilament silk yarn is a promising component for the realization of air stable thermoelectric textile devices.

Graphitic carbon nitride (g-C3N4) has emerged as a promising material for various applications, particularly in the field of energy storage systems. Among these systems, lithium-ion batteries (LIBs) have become the cornerstone of portable electronics and are increasingly being adopted for electric vehicles and renewable energy storage. However, the search for alternative electrode materials that can overcome the limitations of traditional graphite anodes and transition metal oxide cathodes remains a significant challenge. In recent years, g-C3N4 has attracted considerable attention due to its unique physicochemical properties, such as high electrochemical stability, tunable bandgap, large specific surface area, and excellent thermal and chemical stability. Also, the low cost, abundance, and environmental sustainability of g-C3N4 contribute to its suitability for next-generation LIBs. However, the successful utilization of g-C3N4 as an electrode material is hindered by several challenges. This paper aims to explore the challenges and future perspectives of utilizing g-C3N4 as a potential electrode material for LIBs, highlighting the potential benefits and drawbacks of integrating this material into the battery system.

Research on stretchable materials has gained momentum with the increasing commercialization of wearable and flexible devices. Among the materials used in stretchable electronics, polydimethylsiloxane (PDMS) is popular owing to its remarkable mechanical properties when subjected to deformation. Recent studies have shown that sponge-like porous PDMS is gaining attention, as it provides high surface area and strong absorption properties as well as facilitates mass transfer, making it ideal for use in electronics. This review primarily focuses on the production method and application of porous PDMS. The article describes the various processing methods used to produce porous PDMS, including 3D printing, gas foaming, and phase separation, each of which results in different characteristics. Thus, researchers can choose the most suitable method according to their desired application. Porous PDMS provides channels for mass transfer and strong absorption properties that enable addition of fillers such as carbon nanotubes (CNTs), graphene, and metal nanoparticles, which can further enhance the functionality of the material. In addition, the review covers applications according to the filler used, such as sensors using CNT, flexible electrodes using NiO/MnO2/CNT, and nanogenerators using ZnO. Choosing the right material for the filler is important for obtaining the desired characteristics as per its application.

ABSTRACTGraphene is a two-dimensional (2D) material known for its exceptional strength and high electrical conductivity, making it an ideal substance for resistive strain sensors. Recently, fused deposition modeling (FDM) in three-dimensional (3D) printing has gained attractiveness as a promising process due to its ability to produce 3D structured strain sensors by layer-by-layer melting and depositing conductive polymer composites. To ensure reliable strain sensors, comprehending how sensor properties change based on strain direction is crucial. In this study, graphene-based sensors with different slicing angles were successfully fabricated using FDM, enabling systematic study of the effect of strain angles on the performance of graphene-based sensors. The alignment of graphene filaments relative to the direction of applied strain was found to impact the gauge factor (GF) and other important sensor parameters. Our results showed that the 45° pattern exhibited higher sensitivity and stability compared to the 180° pattern, while the GF was greater for the 180° pattern. Additionally, we demonstrated high reliability and linearity through 1000 bending tests. The findings of this study will contribute to the growing body of research on FDM-fabricated graphene-based strain sensors.

Abstract Silver (Ag) nanowires have attracted significant attention as flexible electrodes for various wearable electronic devices owing to their excellent optical and electrical properties. Patterning is an important step in the fabrication of Ag nanowire electrodes of appropriate size and shape for electronic device applications. Among the various methods to pattern Ag nanowires, photolithography using a liquid photoresist is the most widely used. However, some factors have limited an extensive use of this method, such as the non-uniform thickness of liquid photoresist on large-scale coatings and the requirement of a post-annealing step that limits the application to few polymeric substrates. In turn, these factors affect the successful application of the roll-to-roll fabrication process. Dry film photoresist (DFR), a solid-state film-type photoresist, can enable a fast and simple patterning process at lower temperatures, as DFR-based patterning process only requires a simple lamination step to coat the photoresist on the substrates. The DFR process is performed at a temperature below 80 °C, which enables the application of most polymeric substrates. Furthermore, this process doesn’t involve any additional post-annealing process, which makes it an appropriate technology for the roll-to-roll fabrication process. Owing to the advantages of DFR patterning, several recent studies have focused on this process for Ag nanowires patterning. This review provides an overview of successful examples of Ag nanowire patterning based on the use of DFR, along with the application of patterned Ag nanowires substrates as obtained by this method.

With the technological advances in wearable and portable electronic devices, the demands for associated technologies including flexible energy storage devices increase. Among many types of energy storage devices, flexible supercapacitors (FSCs) are highly attractive in comparison with others as they exhibit high power density, high storage density, and mechanical stability. In particular, carbon nanotubes (CNTs) are being widely used as the electrode materials for FSCs, owing to their mechanical strength and outstanding electrical performance. Herein, we classified CNT-based FSCs according to the structural types of CNTs and the materials incorporated. The unique structures and properties of the three types of CNTs (single-walled CNTs (SWCNT), double-walled CNTs (DWCNT), and multi-walled CNTs (MWCNT)) are compared and the mechanisms of FSCs are discussed. Finally, a summary of the overall electrochemical properties and current development of the reported FSC electrodes based on SWCNT, DWCNT, and MWCNT are presented thoroughly.

Ag nanowire electrodes are promising substitutes for traditional indium tin oxide (ITO) electrodes in optoelectronic applications owing to their impressive conductivity, flexibility, and transparency. This review provides an overview of recent trends in Ag nanowire electrode layer formation, including key developments, challenges, and future prospects. It addresses several challenges in integrating Ag nanowires into practical applications, such as scalability, cost-effectiveness, substrate compatibility, and environmental considerations. Additionally, drawing from current trends and emerging technologies, this review explores potential avenues for improving Ag nanowire layer-forming technologies, such as material advancements, manufacturing scalability, and adaptability to evolving electronic device architectures. This review serves as a resource for researchers, engineers, and stakeholders in nanotechnology and optoelectronics, and underscores the relationship between advancements in patterning and the application of Ag nanowire electrodes. Through an examination of key developments, challenges, and future prospects, this review contributes to the collective knowledge base and encourages continued innovation in the ever-evolving realm of Ag nanowire-based optoelectronics.

Abstract With technological advances in wearable health care monitoring system, there increasing demands for the patterning technology for reliable sensors. Dry-film photoresists (DFRs) have several advantages for the patterning of silver nanowires (AgNWs), including cost-effectiveness, low toxicity of the process, and ease of mass production through a roll-to-roll process. In this study, using DFRs, we achieved the facile fabrication of AgNW-based chips for optical detection of myoglobin (Mb) via surface-enhanced Raman spectroscopy (SERS). Mb is found in accessible biological fluids such as urine and serum, which is a representative protein biomarker for human health monitoring. AgNWs were successfully patterned on polyethylene terephthalate films using DFR to form multiple spots, with a diameter of ~500 µm, that are available for detection. SERS spectra showed that the AgNW chips can efficiently detect myoglobin proteins down to levels of clinical significance. Our results will provide insights for the cost-effective production method of futuristic health care monitoring system.

With the technological progress of wearable electronics operated in 5 G network communication system, a stretchable noise suppressor at GHz bandwidth that is reliable under severe deformation coming from the user’s motion should be developed. However, current material systems for the noise suppressor showed a limited stretchability. This study introduces a carbonyl iron powder – polydimethylsiloxane (CIP – PDMS) composite with partially bonded interface as a solution to enhance the stretchability. Modulation of CIP surface to have the partial interface bonding (CIP-PID) results in the ultra large strain of ~165% even at the 40 vol% of CIP-PIDs, while only ~71% of strain is observed for CIPs with the full interface bonding (CIP-FID). According to a microstructural analysis and FEM simulation of the strained composite specimens, when partially bonded to CIP at the interface, the PDMS matrix forms a free surface that can be deformed like pure PDMS, resulting in high stretchability. The wettability of CIP offers protection against eddy current loss while retaining strong magnetic properties, suppressing the EM noise. Thus, the approach eliminates the tradeoff between EM suppression and stretchability.

Precise measurement of the surface energy of nanoscale metal thin films is crucial for the fabrication of reliable miniaturized electronic devices consisting of multi-stacked thin film strips. However, the conventional method utilizing sessile drops to measure the surface energy is not suitable for nanoscale samples owing to the much larger size of the liquid droplets than those of the samples being measured. Herein, nCA-AFM (nano contact angle-atomic force microscopy) based on PF-QNM (PeakForce quantitative nanomechanical mapping) imaging mode is explored as a novel tool to measure the surface energy of nanoscale Au strips. Au strips with thicknesses of 50 and 100 nm were patterned to have widths in a range from 200 to 500 nm. The surface energy of the nano-patterned Au strips measured with PF-QNM methods revealed that grain size is the most important factor determining the surface energy. The sample having different widths with the same grain size showed similar surface energy values, regardless of the sample dimensions. Our results highlight that grain size control is required to achieve the target surface energy of metal strips for applications in nanoscale electronic devices.

With the advance in wearable electronics, there is increasing demand for conductive fibers that are stable under machine washing. Silk-based conductive fibers in particular have attracted significant attention due to their biocompatibility and excellent mechanical properties. To achieve the machine washability of silk-based conductive fibers, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has been adopted as a conductive functional layer. PEDOT:PSS with ethylene glycol has a negative surface charge that can strongly adhere to the positively charged silk surface, leading to the excellent machine washability of silk-based conductive fibers. Various types of PEDOT:PSS/silk-based conductive fibers have been demonstrated in past research, including those in which different types of materials, such as silver (Ag) nanowires, carbon nanotubes, or manganese dioxide (MnO2), have been inserted to produce a range of electrical and chemical properties that can be used for different applications. In this mini-review, strategies to enhance the stability of silk-based conductive fibers using PEDOT:PSS are discussed. Various types of PEDOT:PSS/silk-based conductive fiber are introduced and research trends and future research directions are discussed.

Achieving resistance to sedimentation of carbonyl iron powders (CIPs) in ethanol is important to fabricate reliable magnetorheological suspensions. The traditional method to improve the sedimentation stability is to add dispersants, but this approach can suffer from high costs and toxicity of added surfactants. In this study, the surface of CIPs was modified with 3-aminopropyl triethoxysilane (APTES) or tetraethyl orthosilicate (TEOS) to enhance the sedimentation stability of CIP suspensions without using toxic dispersants. After coating APTES or TEOS on the CIP surface, the surface energy of the CIP powders increased, which was attributed to the increased amino or hydroxyl groups on the CIP surface due to APTES or TEOS, respectively. The Gibbs free wetting enthalpy (ΔG) was calculated to evaluate the wettability of the modified CIPs, and APTES@CIPs or TEOS@CIPs had a low ΔG, indicating that both had a high thermodynamic spontaneity of wetting in ethanol. The enhanced wettability due to APTES or TEOS coating resulted in low CIP agglomeration, which resulted in APTES@CIPs or TEOS@CIPs dispersions having smaller average particle sizes than pure CIP dispersions. Therefore, APTES@CIPs or TEOS@CIPs showed more than 2 times slower sedimentation velocity than pure CIPs, resulting in enhanced sedimentation stability.

The fibrous supercapacitor is a promising candidate for wearable energy-storage systems due to excellent mechanical reliability under deformation. In this study, a mechanically reliable fibrous supercapacitor with high volumetric power density and energy density was developed using fiber electrodes composed of multilayered active materials coated on silk yarns. The conductive silk yarn electrodes are fabricated via a sequential dip-coating process of silver nanowires, multi-walled carbon nanotubes (MWCNT, three to seven walls), and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The composite-coated silk yarn electrodes were stable under cyclic bending as well as under washing in water. Due to the synergetic effect of the three conducting materials, an excellent electrochemical performance was obtained resulting in high volumetric energy and power densities of 8–13 mWh cm−3 and 8–19 W cm−3, respectively. A yarn-type supercapacitor was demonstrated by integrating composite-coated silk yarn electrodes with a hydrogel electrolyte, showing a promising stability as evidenced by the retention of over 94% and 93% of the specific capacitance after 90-degree bending and stretching.

Silver nanowires (AgNWs) are a potential alternative to conventional transparent conductive materials for various applications, such as flexible and transparent electrodes in optoelectronic devices, including touch screens, solar cells, and flexible displays. However, AgNW electrodes face degradation due to environmental factors, electrical instability, and mechanical stress. To overcome these challenges, strategies to protect AgNW-based electrodes via the incorporation of polymeric materials were widely investigated to improve the durability and stability of AgNW-based electrodes. This review paper gives a comprehensive overview of the incorporation of polymeric materials with AgNW electrodes, emphasizing their performance, and applications. We compare the different polymeric materials and their effect on the electrical, optical, and mechanical properties of AgNW electrodes. Furthermore, we evaluate the key factors affecting the choice of protective layers, such as their compatibility with AgNWs, and also we present current challenges and future opportunities for the development of polymeric materials for AgNW electrodes in emerging technologies.

Carbon nanotubes (CNTs), with their extraordinary combination of mechanical, electrical, and thermal properties, have emerged as a revolutionary class of nanomaterials with immense potential in energy storage and harvesting devices. Realizing this potential hinges on a fundamental challenge: the dispersion stability of CNTs within various matrices. This review paper provides a comprehensive exploration of the critical interplay between CNT dispersion stability and its far-reaching implications for the performance of energy storage and harvesting technologies. By delving into the underlying mechanisms of dispersion, the strategies to achieve stability, and the direct effects on device functionality, this review sheds light on the intricate relationship between nanotube dispersion and the advancement of energy-related applications.

Carbon nanotube (CNT)-based electrodes in flexible supercapacitors have received significant attention in recent years. Carbon nanotube fiber fabrics (CNT-FF) have emerged as promising materials due to their high surface area, excellent conductivity, and mechanical strength. Researchers have attempted to improve the energy density and rate performance of CNT-FF supercapacitor electrodes through various strategies, such as functionalization with conductive materials like MnO2 nanoparticles and/or incorporation of graphene into them. In addition, the utilization of CNTs in combination with thin metal film electrodes has also gained widespread attention. Research has focused on enhancing electrochemical performance through functionalizing CNTs with conductive materials such as graphene and metal nanoparticles, or by controlling their morphology. This review paper will discuss the recent developments in supercapacitor technology utilizing carbon nanotube-based electrodes, including CNT fiber fabrics and CNTs on thin metal film electrodes. Various strategies employed for improving energy storage performance and the strengths and weaknesses of these strategies will be discussed. Finally, the paper will conclude with a discussion on the challenges that need to be addressed in order to realize the full potential of carbon nanotube-based electrodes in supercapacitor technology.

Indium tin oxide (ITO) is currently the most widely used material for transparent electrodes; however, it has several drawbacks, including high cost, brittleness, and environmental concerns. Silver nanowires (AgNWs) are promising alternatives to ITO as materials for transparent electrodes owing to their high electrical conductivity, transparency in the visible range of wavelengths, and flexibility. AgNWs are effective for various electronic device applications, such as touch panels, biosensors, and solar cells. However, the high synthesis cost of AgNWs and their poor stability to external chemical and mechanical damages are significant challenges that need to be addressed. In this review paper, we discuss the current state of research on AgNW transparent electrodes, including their synthesis, properties, and potential applications.

Optimizing the coating conditions for a doctor blading system is important when seeking to improve the performance of Ag nanowire electrodes. In this study, the effect of the blading height and speed on the optical and electrical properties of Ag nanowire electrodes was investigated. Ag nanowires were first spread on a PET substrate using a doctor blade with differing heights at a fixed blading speed. An increase in the blading height resulted in the degradation of the optical transmittance and stronger haze due to the higher probability of Ag nanowire agglomeration arising from the greater wet thickness. When the blading speed was varied, the optical transmittance and haze were unaffected up until 20 mm/s, followed by minor degradation of the optical properties at blading speeds over 25 mm/s. The higher speeds hindered the spread of the Ag nanowire solution, which also increased the probability of Ag nanowire agglomeration. However, this degradation was less serious compared to that observed with a change in the blading height. Therefore, optimizing the blading height was confirmed to be the priority for the production of high-performance transparent Ag nanowire electrodes. Our study thus provides practical guidance for the fabrication of Ag nanowire electrodes using doctor blading systems.

In the battery field, carbon nanotubes (CNTs) attract much attention due to their potential as a supporting conducting material for anodes or cathodes. The performance of cathodes or anodes can be optimized by introducing densely packed CNTs, which can be achieved with high dispersibility. The efficiency of CNT usage can be maximized by enhancing their dispersibility. An effective technique to this end is to incorporate surfactants on the surface of CNTs. The surfactant produces a surface charge that can increase the zeta potential of CNTs, thereby preventing their agglomeration. Additionally, surfactants having long chains of tail groups can increase the steric hindrance, which also enhances the dispersibility. Notably, the dispersibility of CNTs depends on the type of surfactant. Therefore, the results of dispersibility studies of CNTs involving different surfactants must be comprehensively reviewed to enhance the understanding of the effects of different surfactants on dispersibility. Consequently, this paper discusses the effect of different types of surfactants on the dispersibility of CNTs and presents several perspectives for future research on dispersibility enhancement.

Currently, there is an increasing demand for portable and wearable electronics. This has necessitated the development of stretchable energy storage devices, while simultaneously maintaining performance. Hence, the electrodes and electrolyte materials used in stretchable supercapacitors should be robust under severe mechanical deformation. Polymers are widely used in the fabrication of stretchable supercapacitors. It is not only crucial to choose good polymer candidates with inherent advantages, but it is also important to design suitable polymer materials for both electrodes and electrolytes. This mini-review explains the concept of stretchable supercapacitors, the theoretical background of polymer-based electrodes for supercapacitors, and the fabrication strategies of stretchable electrodes for supercapacitors. Finally, we present the drawbacks and areas that still need to be developed.

Surface energy characterization is important to design the fabrication process of reliable electronic devices. Surface energy is influenced by various factors such as surface functionality and morphology. Owing to the high surface-to-volume ratio, surface energy at the nanoscale can be different from that of the bulk. However, the conventional methods for characterization of surface energy such as a sessile drop or Washburn methods cannot be used for nanoscale samples, owing to the limited volume for characterization. Recently, surface energy characterization on the nanoscale using atomic force microscopy (AFM) with Peak Force-Quantitative Nanomechanical Mapping (PF-QNM) imaging mode has been proposed. The nanoscale AFM tips measure the adhesion forces at the nanoscale, which are converted into surface energy through pre-calibrated curves. Successful surface energy characterization of nanoscale metal samples using AFM with the PF-QNM method has been reported previously. This mini-review discusses the recent progress on surface energy characterization at the nanoscale using AFM with the PF-QNM method. The fundamentals of the PF-QNM mode are introduced, and the results of surface energy characterization are summarized. Consequently, the future research direction for surface energy characterization at the nanoscale is discussed. [ABSTRACT FROM AUTHOR]

This study reviews the potential of flexible strain sensors based on nanomaterials such as carbon nanotubes (CNTs), graphene, and metal nanowires (NWs). These nanomaterials have excellent flexibility, conductivity, and mechanical properties, which enable them to be integrated into clothing or attached to the skin for the real-time monitoring of various activities. However, the main challenge is balancing high stretchability and sensitivity. This paper explains the basic concept of strain sensors that can convert mechanical deformation into electrical signals. Moreover, this paper focuses on simple, flexible, and stretchable resistive and capacitive sensors. It also discusses the important factors in choosing materials and fabrication methods, emphasizing the crucial role of suitable polymers in high-performance strain sensing. This study reviews the fabrication processes, mechanisms, performance, and applications of stretchable strain sensors in detail. It analyzes key aspects, such as sensitivity, stretchability, linearity, response time, and durability. This review provides useful insights into the current status and prospects of stretchable strain sensors in wearable technology and human–machine interfaces. [ABSTRACT FROM AUTHOR]

Magnetorheological fluids (MRFs) is a smart fluid system that exhibits swift and reversible alterations in their rheological characteristics when exposed to an external magnetic field. MRFs are used for applications in various areas, including automotive systems, robotics, aerospace, and civil engineering. The performance of MRFs depends on the behavior of the dispersed magnetic particles, necessitating thoughtful consideration of particle traits to optimize fluid performance. Carbonyl Iron Powders (CIPs), high purity iron (>98%) reduced from penta carbonyl iron, are widely employed in MRFs due to their exceptional magnetic characteristics. Nevertheless, the innate surfaces of CIPs tend to conglomerate, leading to compromises in fluid stability and rheological performance. To overcome the challenges, an intensive research has been devoted to advancing surface modification techniques that augment the dispersion, stability, and overall functionality of MRFs based on CIPs. This review describes the comprehensive approach to surface modification of CIPs for highly stable MRFs. We discuss the various surface modification methodologies that have been explored to optimize the behavior of carbonyl iron-based MRFs. Coating techniques, surfactant functionalization, magnetic coatings, and emerging approaches such as nanocoatings and electrochemical modification are also summarized. Moreover, insights into potential applications and future prospects of these modified MRFs are provided. [ABSTRACT FROM AUTHOR]

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), one of the conducting polymers, is widely used as a conducting material in various applications. PEDOT:PSS possesses high electrical conductivity, optical transparency in visible light range, good chemical and physical stability in ambient state, etc. Furthermore, PEDOT:PSS offers the advantages of flexibility and possibility of solution-based process, which makes it suitable for use in flexible electronic devices. In this mini review, the applications of PEDOT:PSS as a conductive parts in energy harvesting and storage technologies are discussed and summarized. [ABSTRACT FROM AUTHOR]