Controllable Triboelectric Series Using Gradient Positive and Negative Charge-Confinement Layer with Different Particle Sizes of Mesoporous Carbon Materials.

As a method to maximize the energy efficiency of triboelectric nanogenerators (TENGs), high-voltage charge injection (HVCI) on the surface is a simple and effective method for increasing surface charge densities. In this study, positive and negative triboelectric series are controlled using a 3-layer gradient charge-confinement wherein the particle sizes of the mesoporous carbon spheres (mCSs) are sequentially arranged depending on the external surface area of the mCSs. In the gradient charge-confinement layers of this study, the mCS with different sizes perform charge transport from the surface to a deep position during HVCI while mitigating the charge loss through charge confinement to induce the high space charge densities. Through this process, the output voltage-which is initially 15.2 V-is measured to be 600 V after HVCI, thus representing an increase of about 40 times. Further, to amplify the low output current, which is a disadvantage of triboelectric energy, two types of electrical energy-triboelectric and electromagnetic energy-are produced in single mechanical motion. As a result, the output current produced by the cylindrical TENG and electromagnetic generator is recorded as being 1300 times higher, increasing from 12.8 µA to 17.5 mA.

Controllable Physical Synergized Triboelectricity, Shape Memory, Self-Healing, and Optical Sensing with Rollable Form Factor by Zn cluster.

To build devices offering users comfortable experience, it is important to focus on form factor and multifunctionality. In this study, for the first time, multifunctional Zn clusters with shape memory, self-healing, triboelectricity, and optical sensing synergized with rollable form factor are designed and fabricated by coordinating COO- and Zn2+ . As pore forming agent, Zn clusters produce hierarchical porous structure depending on Zn amount. Zn clusters are applied as message transmitters and charge containers in optical sensing and corona charge injection, respectively. Moreover, Zn clusters in PVB-COO-Zn serve as positive tribomaterial due to Zn ion doping effect, increasing the output performance as the Zn amount reaches 20 wt%. In addition, injecting positive charge into PVB-COO-Zn 20 lead to more than 24 times increase in output performance compared to those of non-porous structures. The reversibility of Zn clusters endows shape memory and self-healing, synergized with the rollable form factor. The rollability is implemented using the long alkyl chain and the energy absorption of porous structure, providing damage resistance. The advancements in this work provide opportunities for multifunctional and unique applications (shape memory rotating-triboelectric nanogenerator, rollable self-healing touchpad, hidden tag) synergized with rollability that accomplishes working in broadened condition in near future.

Vertically and Horizontally Drawing Formation of Graphite Pencil Electrodes on Paper by Frictional Sliding for a Disposable and Foldable Electronic Device.

The objective of this study is to fabricate an electrode by frictional sliding caused by a rough paper surface. The pressure exerted during drawing induces adsorption of the graphite particles by the rough paper and simultaneously reduces the surface roughness of the paper electrode. Repetitive drawing in one-way direction reduced the roughness of the paper surface, decreasing the grain boundaries of graphite. This increases the electron pathway at the electrode, thus reducing the resistance to less than 50 Ω. At the same time, repetitive drawing could confirm that unstable errors caused by the hand could help converge within a certain margin of error. We quantified the relationship between pressure and resistance when drawing on the electrode using a pencil hardness tester. In addition, the electrodes formed by repeated drawing generated a new surface grain and boundary, parallel to the drawing direction, and changed the electrode characteristics with respect to the drawing direction. The grain boundary difference based on the drawing direction was measured via a heating test of the foldable device, a sound pressure level, and laser scattering vibrometer measurements of a linear speaker. The fabricated graphite electrodes can be used in disposable foldable paper electronics because they are prepared using inexpensive materials.