Inspired by the sensory organs of spiders, crack-based strain sensors are flexible sensors fabricated by depositing a thin layer of metal onto a stretchable polymer. However, to date, most studies on crack-based sensors have considered only linear strain, even when bending is considered, which do not analyze how sensor resistance depends on complex strains (linear, convex, and concave). For each given type of strain, this study examined how the distance between cracks depends on the crack direction. This study also analyzed how the crack-generation mechanism depends on the relation between film-bending axis and crack direction. Thus, a device was proposed herein to test the crack-based sensors and demonstrate how this device can be used to measure the bending direction.
Industrialization around the globe has rapidly increased fine dust concentration in the air, deteriorating the air quality. Deteriorated air quality greatly affects human health, causing diseases, such as respiratory and heart diseases. Thus, nanofibrous air filters with high dust removal efficiency and light transmittance on window screens have been investigated. However, nanofiber deformation due to external conditions and low nanofiber production of conventional electrospinning systems bottleneck their practical applications. In this study, we report a humiditycontrollable, high-throughput, patternable, repairable, and portable electrospinning-based filter coating system. The fabricated nanofibrous filter had a high dust removal efficiency (>90%), high transparency (>80%), and low pressure drop (<60 Pa). Moreover, we fabricated nanofibrous fibers in a humid environment by adjusting the relative humidity (45−71%) and patterned and repaired the nanofibrous dust filter. The proposed filter coating method offered excellent performance in the actual outdoor environment.
The patterning of electrospun fibers is a key technology applicable to various fields. This study reports a novel focused patterning method for electrospun nanofibers that uses a cylindrical dielectric guide. The finite elements method (FEM) was used to analyze the electric field focusing phenomenon and ground its explanation in established theory. The horizontal and vertical electric field strengths in the simulation are shown to be key factors in determining the spatial distribution of nanofibers. The experimental results demonstrate a relationship between the size of the cylindrical dielectric guide and that of the electrospun area accumulated in the collector. By concentrating the electric field, we were able to fabricate a pattern of less than 6 mm. The demonstration of continuous line and square patterning shows that the electrospun area can be well controlled. This novel patterning method can be used in a variety of applications, such as sensors, biomedical devices, batteries, and composites.
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