Tomoya Koshi

Self-healing metal wire using electric field trapping of metal nanoparticles

We propose a self-healing metal wire using electric field trapping of gold nanoparticles by a dielectrophoresis force. A cracked gold wire can retrieve its conductivity through the self-healing function. In this paper, we examine the healing voltage causing the electric field trapping and determine the healing time, which is relevant to future device applications. First, the forces acting on a nanoparticle are analyzed and a theoretical healing voltage curve is calculated. Then, gold wires with 200- to 1,600-nm-wide cracks are fabricated on glass substrate and the self-healing function is verified through healing experiments. As a result, gold wires with cracks of up to 1,200 nm in width are successfully healed by applying less than ~2.5 V (on average), and the experimental results correspond almost exactly with the calculated healing voltage curve. The average healing times are 10 to 285 s for 200- to 1,200-nm-wide cracks. Through scanning electron microscope analysis after the healing experiments, we confirm that the cracks are healed by assembled nanoparticles.

Crack-Configuration Analysis of Metal Conductive Track Embedded in Stretchable Elastomer

This paper reports the analysis of the crack configuration of a stretched metal conductive track that is embedded in a stretchable elastomer. The factor determining the crack configurations is analyzed by modeling as well as experiments. The modeling analysis indicates that the crack configuration is determined by the ratio of the elongation stiffness of the track and elastomer, and is classified into two types: multiple-crack growth and single-crack growth. When the track stiffness is considerably lower than the elastomer stiffness, multiple-crack growth type occurs; in the opposite case, single-crack growth type occurs. Hence, to verify the modeling analysis, metal conductive tracks with different thicknesses are fabricated, and the cracks are studied with respect to the crack width, number of cracks, and crack propagation speed. In this study, two conventional metal-track shapes are studied: straight-shaped tracks with track thickness of 0.04–1.17 µm, and wave-shaped tracks with track thickness of 2–10 µm. For straight-shaped tracks, multiple-crack growth type occurred, when the track thickness was 0.04 µm, and the crack configuration gradually changed to a single crack, with the increase in the track thickness. For wave-shaped tracks with track thickness of 2–10 µm, only single-crack growth type occurred; however, the crack propagation speed decreased and the maximum stretchability of the track increased, with the increase in the track thickness.

Novel Social Innovation Concept Based on the Viewpoint of the Infrastructure User

Recently, due to the deceleration of the markets in developed economies, the growing demand for infrastructure development in emerging countries has become more important in the global economy. Conventionally, developed countries have improved their infrastructure from governments and suppliers viewpoints. However, this approach has not always been the best when working in emerging countries. In this study, we propose an innovative approach inspired by the concept of social innovation, centered around the social viewpoint. It consists of a system for the successful implementation and sustainable development of new infrastructure projects in emerging countries. We focus on an ongoing railway project in Vietnam by looking at the applicability of this concept there. Finally, the concept is evaluated through rounds of discussion with experts from the government, academia and industry. It was concluded that the project is perceived to have great potential for the region, and it is regarded with high esteem by all stakeholders.

Stretchable electronic device with repeat self-healing ability of metal wire

This paper reports a stretchable electronic device with repeat self-healing ability of a wire crack caused by stretching deformation. The crack of metal wire is healed with assembled metal nanoparticles by dielectrophoresis, when a voltage is applied to the cracked wire covered with the nanoparticle solution. By designing a circuit, we controlled the applied voltage and current for the self-healing to be avoid excessive Joule heating in the assembled nanoparticles. This consideration enables us to heal a crack of tens of micrometers in width and to practically achieve a stretchable electronic device.

Self-healing metal wire using an electric field trapping of gold nanoparticles for flexible devices

We developed a self-healing metal wire using an electric field trapping of gold nanoparticles. A cracked metal wire on a stretchable substrate can get its conductivity again by the self-healing function. In this paper, first, we theoretically analyzed force acting on a nanoparticle and calculated a critical voltage which cause the electric field trapping. Next, we fabricated gold wires with artificially patterned cracks on a glass substrate and verified the self-healing function by experiments of a crack healing. Finally, we demonstrated the self-healing of a cracked metal wire on a stretchable substrate to show a usefulness of the self-healing for flexible devices.