Porous Polydimethylsiloxane Elastomer Hybrid with Zinc Oxide Nanowire for Wearable, Wide-Range, and Low Detection Limit Capacitive Pressure Sensor

We propose a flexible capacitive pressure sensor that utilizes porous polydimethylsiloxane elastomer with zinc oxide nanowire as nanocomposite dielectric layer via a simple porogen-assisted process. With the incorporation of nanowires into the porous elastomer, our capacitive pressure sensor is not only highly responsive to subtle stimuli but vigorously so to gentle touch and verbal stimulation from 0 to 50 kPa. The fabricated zinc oxide nanowire–porous polydimethylsiloxane sensor exhibits superior sensitivity of 0.717 kPa−1, 0.360 kPa−1, and 0.200 kPa−1 at the pressure regimes of 0–50 Pa, 50–1000 Pa, and 1000–3000 Pa, respectively, presenting an approximate enhancement by 21−100 times when compared to that of a flat polydimethylsiloxane device. The nanocomposite dielectric layer also reveals an ultralow detection limit of 1.0 Pa, good stability, and durability after 4000 loading–unloading cycles, making it capable of perception of various human motions, such as finger bending, calligraphy writing, throat vibration, and airflow blowing. A proof-of-concept trial in hydrostatic water pressure sensing has been demonstrated with the proposed sensors, which can detect tiny changes in water pressure and may be helpful for underwater sensing research. This work brings out the efficacy of constructing wearable capacitive pressure sensors based on a porous dielectric hybrid with stress-sensitive nanostructures, providing wide prospective applications in wearable electronics, health monitoring, and smart artificial robotics/prosthetics.

Single Step Growth of Vertically Oriented Zinc Oxide Nanowire Using Thermal Evaporation

Commonly, the synthesis of ZnO nanowires involves the use of metal catalyst via a non-direct step growth which contribute to the contamination on the final product. Thus, in this work we synthesized catalyst-free ZnO nanowires using a direct or single step growth of nanowires. Thermal evaporation method is used to synthesize ZnO nanowires on bare glass substrates with different distances between Zn powder and the substrates; on-top (1.2 cm), 16 cm and 18 cm. Field Emission Scanning Electron Microscopy images showed a vertically well-aligned with high density of ZnO nanowires were successfully synthesized via self-seeding process and the longest nanowires were produced at the shortest distance. Energy Dispersive X-ray and X-Ray Diffraction analyses confirmed that high purity of ZnO nanowires were obtained and ZnO (002) strongest and sharp peak was observed, indicating preferentially grown ZnO nanowires along the c-axis perpendicular to the substrates and leading towards single crystal structure. Four peaks were observed in visible range from Photoluminescence spectra (PL) which related to fundamental defects with the highest peak at 3.04 eV. The on-top sample with distance 1.2 cm from Zn powder has the lowest transmittance due to the high thickness of ZnO nanowires. The range of energy band gap for ZnO nanowires obtained from the extrapolation graph is in agreement with PL highest peak approximately 3.00 eV. Therefore, this direct or single step deposition method is of great interest since it has successfully produced ZnO nanowires with significant characteristics without employing the non-direct step growth.

Elastocaloric effect in zinc oxide nanowire

In this work, zinc oxide (ZnO) nanowire is proposed for elastocaloric application which has been overlooked until now. The elastocaloric effect ([Formula: see text]CE) is calculated by Maxwell relation. The large elastocaloric temperature and entropy change evaluated as 17 K and 28 J/kgK, respectively, at 300 K correspond to the stress of 12 GPa or strain of 5.5% by the simulation data. The elastocaloric temperature can be increased to 22 K under the operating tempering of 600 K. However, [Formula: see text]CE estimated from the experimental data is found as 2.6 K at 300 K, which corresponds to stress of 6 GPa. These results are expected to significantly expand the knowledge of ZnO nanomaterials as a potential candidate for [Formula: see text]CE. The results are based on the indirect approximation; hence, a direct measurement is needed to verify the obtained results.