Wearable strain sensors translate mechanical deformations into electrical signals for healthcare monitoring. However, the limited ductility of conductive metals and polymers to maintain its conductivity under high degree of mechanical deformation is a crucial problem in existing fabrication methods for strain sensors. In this study, an intrinsically conductive and highly stretchable liquid metal (LM)/carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composite-based wearable strain sensor with electromagnetic wave (EMW)-absorbing properties was explored. The effect of CNT inclusion in the LM/PDMS composites was investigated, revealing enhanced electrical conductivity and EMW-absorbing characteristics without additional mechanical sintering. Through a comprehensive evaluation considering electrical resistance, stretchability, and EMW-absorbing properties, LM/CNT/PDMS composites with 1.5 wt

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.

Graphene 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 degrees pattern exhibited higher sensitivity and stability compared to the 180 degrees pattern, while the GF was greater for the 180 degrees 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.

With the technological development of wearable devices, there are increasing demands for stretchable conductor that have stable electro-mechanical performance. In this study, a stretchable PDMS composite electrodes using ternary systems of fillers consisting of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) / carbon nanotube (CNT) / silver nanowire (AgNW) is explored in a perspective of electro-mechanical response. PDMS matrix is mixed with binary fillers of CNT and PEDOT:PSS, which is followed by AgNW peeling-off process. The PDMS composite is mechanically reliable especially under tensile deformation, which showed a high rupture strain of ~102 % and tensile strength of ~2.7 MPa. In addition, the PDMS composites shows the stable electro-mechanical response, where high electrical conductivity is sustained even under stretchable conditions, showing an electrical resistance value of ~11.7 Ω/cm under 40% of strain. As a demonstration, a supercapacitor using the PDMS composites is demonstrated that shows reliable electrochemical performance.

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.

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.

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.