Visualized Strain Sensor Based On Electrochromic Gel And Transparent Electrode

Strain sensors are widely used in aerospace,military equipment,medical health,robotics and other fields.With the development of modern science and technology,traditional sensors based on semiconductor or metal materials become difficult to meet the requirements of the new generation of the sensors of high flexibility,sensitivity,portability and usability.In recent years,flexible strain sensors based on various organic materials have been developed rapidly,and flexible strain sensors with high sensitivity and large deformation ability have been successfully applied to wearable devices,robots,medical equipment and other fields.Existing flexible strain sensors generally need to be used in conjunction with special signal output equipment,and their complex structure limits their popularization and use.The development of the new flexible sensors with direct stress visualization function but no special display terminal is of great significance for the future development of science and technology.In response to the above problems,this paper develops a flexible visualizated strain sensor by introducing organic electrochromic dyes and lithium ions into polyacrylamide gel(PAAm)and combining with silver nanoparticles(AgNWs)transparent electrodes.The specific contents include:①Organic gel with both electrochromic and piezoresistive properties.By freeze-drying,the PAAm hydrogel was transformed into a PAAm aerogel skeleton,and after swelling in a dimethyl sulfoxide solution containing organic electrochromic pigments,a PAAm organic gel with electrochromic function was obtained.Thanks to the Li~+ions added during the preparation of the hydrogel,the prepared PAAm organic gel exhibits excellent piezoresistive properties,and its compressive strain sensitivity can reach 0.43.After 1000 cycles of fatigue testing,its relative change in resistance is only decreased by 5%.Compared with hydrogels,the moisture retention properties of PAAm organic gels are significantly improved,and the weight loss rate is reduced by 50%.Combining the electrochromic and piezoresistive characteristics of organic PAAm gels,the direct visual monitoring of stress distribution is achieved.②Transparent electrode based on silver nanowires.Taking AgNWs as conductive material and silicone rubber(PDMS)as flexible substrate,a transparent stretchable conductive film was successfully prepared by suction filtration.The transmittance of the prepared Ag NW/PDMS thin composite film in the visible range is greater than 70%,and the conductivity can be up to 5.3 S/cm.Because AgNWs are evenly embedded in the surface layer of PDMS substrate,the adhesion between conductive Ag NW layer and PDMS substrate is strong and the adhesion strength is up to 3 MPa.The Ag NW/PDMS film maintains a good stability in mechanical and electrical properties after 1000 cycles of loading test at a frequency of 1Hz and a strain of 10%,indicating its suitability for stretchable transparent electrodes.③Visualized and stretchable strain sensor.Combining PAAm organic gel with electrochromic and piezoresistive properties and transparent electrodes based on silver nanowires,a flexible strain sensor with a sandwich structure was prepared.The sensor not only can properly detect tensile strain,but also can directly visualize the distribution of stress and strain through the force-electrochromic reaction,eliminating the need for additional display devices and greatly simplifying the structure of sensors.In addition,this strain sensor has a good stretchability,showing its applicability for wearable devices,electronic skin,aerospace and other large deformation monitoring fields.