| Nowadays,the development of Information Society is inseparable from data acquisition,transmission and processing.Pressure sensor is one of the most commonly used micro electro mechanical systems（MEMS）in signal acquisition by sensing pressure changes and then converting them into electrical signals that a computer can process.With the rapid development of flexible electronics and emerging technologies such as electronic skins,human-computer interactions and wearable electronic devices,flexible pressure sensors have been paid much attention.Piezoresistive flexible pressure sensor has gradually become a research hotspot because of its advantages of simple fabrication process and anti-interference property.In this paper,we designed a piezoresistive flexible pressure sensor based on cross-scale microstructures to achieve the trade-off of sensitivity and pressure sensing range.The flexible pressure sensor was well applied into multiscale pressure sensing and fine-grained identification.Besides,to improve the environmental tolerance of the flexible pressure sensor,we designed a superhydrophobic protective layer used for the sensor encapsulation,and systematically investigated the superhydrophobicity,mechanical durability and self-cleaning property of the protective layer.The introduction of microstructures such as pyramid and dome arrays into the flexible pressure sensors has been proved to be an effective way to improve the performance of the sensors.The honeycomb structure in biology is composed of hexagonal cells with excellent geometric and mechanical properties,which has been widely used in materials science.In this paper,some stainless steel balls with the same diameter were hexagonal close-packed and then used as template of honeycomb-shaped structure.Flexible and transparent polydimethylsiloxane（PDMS）was chose to replicate the honeycomb-shaped structure and then was covered by multi-walled carbon nanotubes（MWCNTs）,namely PDMS/MWCNTs conductive layer.Finally,a piezoresistive flexible pressure sensor was obtained by assembling two copper foil electrodes with the PDMS/MWCNTs conductive layer as a sandwich structure.The influence of different structure parameters of the honeycomb-shaped structure on the performance of the flexible pressure sensor was discussed in detail,taking the bottom thickness and diameter of the honeycomb-shaped structure as main variables.The piezoresistive flexible pressure sensor with the optimal parameters was found to show extremely fast response and recovery time（45ms and 35ms）.In addition,the sensor possesses a sensitivity of 25.7k Pa-1 in the pressure range of 0-0.56k Pa,2.3k Pa-1 for 0.56-20.4k Pa,and a widely linear sensing range（20.4-460k Pa）at high pressure with a sensitivity of 0.13k Pa-1.The flexible pressure sensor shows an excellent stability up to 9500 loading-unloading cycles.In practical application,the flexible pressure sensor can be used to detect and recognize the signals of human motions,such as pulse,joint curvature,swallowing,speaking,and so on.Furthermore,in order to improve the environmental tolerance of the flexible pressure sensor,we designed a superhydrophobic protective layer based on a non-fluorinated flexible Zn/PDMS film-substrate system with labyrinth-like wrinkles.Excellent superhydrophobicity with contact angle（CA）up to 168.5°and slide angle（SA）low to 0°has been achieved on the Zn/PDMS surface,which is attributed to the micro/nano-textured structures of the labyrinth-like wrinkles,providing sufficient air pockets to form stable Cassie-Baxter state.Hydrophobic surfaces with various CA were obtained by tailing the Zn film thickness,which determines the structure characteristics of the forming labyrinth-like wrinkles.For example,the CA increases to 168.5°from 121.2°with the increase of Zn film thickness from 35nm to 352nm.Furthermore,the Zn/PDMS surface maintains excellent superhydrophobicity under stretching,bending,and twisting mechanical deformation up to 500cycles,due to the stability of the micro/nano-textured structures of the labyrinth-like wrinkles protected by the fantastic self-healing ability of the micro-cracks.Additionally,the Zn/PDMS superhydrophobic surface possesses an outstanding self-cleaning performance for various contaminants.The non-fluorinated flexible superhydrophobic surfaces with superb mechanical durability and self-cleaning property are promising as functional layers for flexible electronics,wearable devices and biomedical engineering etc. |
