Jong-Jin Park

Enhancing the dielectric properties of polymer composites through particulate inorganic fillers 0D has been widely explored as an effective strategy to improve the energy‐harvesting performance of triboelectric and piezoelectric devices. Compared with conventional particulate fillers, 1D fillers offer intrinsic structural anisotropy and enlarged polymer–filler interfaces that favor interfacial polarization and charge transport. However, the intrinsically isotropic crystallization behavior of inorganic salts hinders the formation of long‐range ordered 1D structures, leaving one‐dimensional inorganic salt fibers largely unexplored as functional fillers. Here, we propose a template‐guided directional crystallization strategy to construct 1D potassium chloride (KCl) fibers as functional fillers. The resulting fibers reach macroscopic lengths of up to ∼6 cm and retain continuous crystalline morphology within polymer matrices, thereby enabling extended polymer–filler interfaces. As a result, the fiber‐based composites exhibit enhanced dielectric performance over particle‐filled composites. Multi‐scale characterization reveals that the 1D fibrous structure promotes interfacial polarization and guides dipole alignment within the polymer matrix. Furthermore, the fiber‐enhanced PENG was integrated into a wearable sensing platform for real‐time monitoring and recognition of human motion with machine learning. This work demonstrates that one‐dimensional inorganic salt fibers, as functional fillers, provide an effective strategy for enhancing interfacial polarization in flexible energy‐harvesting systems.

Wearable self‐powering sensors based on triboelectric nanogenerators (TENGs) emerging as a promising strategy for a wide range of applications, such as self‐powering and energy‐harvesting systems, are widely used in healthcare and displacement current are utilized as the driving force. Although the TENG theory is rooted in the displacement current equation proposed by Maxwell, the magnetic field created by this current is often overlooked in TENG research. In this work, an effective charge‐trapping method based on the magnetization current induced by transition metal ion chelation is reported. The experimental results, along with a theoretical analysis of the Maxwell equation and a discussion of the charge‐trapping mechanism, demonstrate that magnetic materials provide enhanced charge‐trapping performance. Transition metal ions chelated to mesoporous silica particles (MSPs) can slightly assign weak paramagnetic properties owing to the formation of ligand complexes. As a result, they can generate a feeble quasi‐magnetization current during the TENG cycle, which enhances the surface charge density of the Co‐MSPs‐based polyvinyl alcohol TENG (PVA‐TENG) by 68%. In addition, it is confirmed that the MSPs chelated with transition metal ions exhibit antibacterial properties, thereby providing promising synergistic effects from the perspective of application as a wearable TENG‐based antibacterial sensor system.

With the development of electronic technology, triboelectric-based sensors have been widely researched in fields such as healthcare, rehabilitation training, and sports assistance due to their manufacturing convenience and self-powering advantages. Among them, 3D fabric-based triboelectric sensors not only possess advantages such as easy mechanized production, good breathability, and ease of wearing but also their unique 3D structure enhances the specific surface area, thereby amplifying the sensitivity. This study proposes a 3D bristle-structured fabric made by a digital knitting technology that has not been studied widely for triboelectric devices. By applying the 3D bristle structure with a large specific surface area to the single jersey fabric, the effective contact area during friction can be increased, resulting in a higher surface charge density. Additionally, the microcapacitor-like effect provided by the numerous microstructures allows the device to store more surface charge, further improving the output performance. The study systematically investigates the output performance of four different structures assembled by single jersey and 3D bristle-structured fabrics. The optimal sample exhibits a 57% higher output voltage than that of the reference 2D fabric sample. The 3D bristle-structured fabric demonstrates linear high sensitivity and distinct output performance when used as a sensor. Finally, a machine learning integration is applied to judge motion to assist a baseball pitcher in a self-training system.

With the increasing focus on triboelectric‐based sensors, research on synthesizing dielectric layers from specific substances is gradually emerging. Despite numerous negatively‐charged triboelectric materials, there is a scarcity of synthesizable positively‐charged materials, creating a research gap. This study demonstrates the molecular design of a conjugated, mesoporous, self‐assembled sheet via bottom‐up synthesis. The synthesized sheet is functionalized to create a triboelectric nanogenerator. Its large specific surface area, softness, and internal space increase the actual contact area and provide adsorption sites for polypyrrole nanoparticles. The incorporation of ‐COO functional group enhances positive triboelectric performance, forming a dielectric layer with charge‐trapping capabilities. When contact with polytetrafluoroethylene (PTFE), this structure boosts the output voltage, showing significant amplification after charge injection with minimal decay. As a demonstration, the bilayer structure is applied as a touchpad on the experimenter's arm to write symbols. The signals are input into an innovative machine‐learning model to interpret the writer's intent. Additionally, the device connects to a terminal for real‐time medical services, suggesting practical applications for wearable triboelectric sensors with artificial intelligence.

The demand for clean-energy collection has gradually increased in recent years, making triboelectric nanogenerators a promising research field, because of their advantages in convenient manufacturing, diversified materials, and diverse synthesis and modification possibilities. However, recent studies indicate that charge decay, a major limiting factor in the triboelectric output, prevents the induced charge from combining with the bottom electrode, leading to charge loss. The use of charge-trapping sites to retain the induced charge generated during the friction process is an important solution in the field of triboelectric nanogenerator research. This study proposes the use of an elastic ink with macroscopic magnetism as trapping sites by coating the ink as dots between the polytetrafluoroethylene (PTFE) dielectric layer and the electrode layer. Nickel particles in the magnetic ink are doped into the system as microcapacitors, which prevent the combination of the friction layer and induced charges on the back electrode. Because the nickel itself can be used as a charge-potential trap to capture the charge introduced by the charge-injection process, the charge can be maintained for a long time and achieve a long-term high-output state. The output voltage was more than 6 times that of the reference group without the magnetic-ink coating after 3 h. The results provide a reference direction for research on preventing charge decay and trapping charges in triboelectric nanogenerators.

To further improve the output performance of triboelectric devices, reducing charge attenuation and loss has become a hot research topic. Particularly, textiles have emerged as one of the promising research directions for triboelectric devices owing to their special internal structure and large specific surface area. In the present work, polyacrylonitrile fibers are fabricated with two distinct structures to provide a higher dielectric constant due to the strong polar properties brought about by higher dipole moment of the CN group. In addition, the complex and closely connected structure of the textile increases specific internal surface area. As a friction layer, the output voltage is shown to increase to 625% of the initial value (from 8 to 60 V) after the application of friction for a short time due to accumulation property. When acting as a trapping layer, the charge loss after injection is effectively prevented due to excellent charge trapping effect. After 24 h, the triboelectric output performance remains at ≈70% of the initial value (decreasing from 320 to 220 V), which is more than 20 times that of the polytetrafluoroethylene film, which decreases from 125 to 19 V. The device is realized for the advanced application of multi‐modal sensors.

A composite with shape memory‐assisted self‐healing and piezoresistive sensing ability is presented herein, and its high conductivity is attributed to a small amount of well‐dispersed carbon black (CB). Carboxylic acid groups are introduced into the polyvinyl butyral (PVB) side chain via the ring‐opening reaction of succinic anhydride. Thus, CB is well‐dispersed in the solution owing to simultaneous attraction and electrostatic repulsion. The resulting ink with less than 30 wt.% CB is highly conductive (3.7 S cm⁻¹). In addition, hexamethylene diisocyanate (HDI) is used as a crosslinking agent to promote the reaction between OH and COOH in the side chains of the PVB‐COOH. The dual network consisting of urethane and amide bonds exhibits the shape memory effect. Moreover, the composite is shown to be capable of shape memory‐assisted self‐healing owing to the hydrogen bonds between the dual network and COOH, such that the resistance returns to its initial value, and the healed sample can support a 1 kg weight. The resulting multi‐modal sensing system is shown to detect bio‐signals such as body movements, breathing, and pulse. In summary, the present work provides an effective strategy for the development of conductive composite electrodes for various applications that require adaptability and piezoresistive sensing ability.