Construction And Application Of Silk Fabric-based Energy And Sensing Devices

With advances of electronic science and technology,more electronic devices have been developed in recent years.Among them,wearable electronic devices attract the most interest due to their great potentials in medical monitoring,sports rehabilitation,communication and entertainment.Compared with the conventional electronic device,wearable devices possess excellent flexibility,which can meet the requirements of different working environment.Currently,one of the main challenges in wearable electronics is to develop miniaturized energy supply systems with excellent flexibility,which can be integrated with other electronic elements to form a smart wearable device.Textile is an ideal material to serve as the substrate of wearable devices.Although textile could provide excellent flexibility,its relative rough surface greatly limits its application in electronic devices.Therefore,there is an urgent need to functionalize conventional textiles for the fabrication of flexible electronic elements.In this thesis,silk fabric was selected as the substrate materials to prepare textile-based wearable electronic elements.The main works are summarized as follows:1.Silk fabric-based wearable thermoelectric generator for energy harvesting from human bodyHerein,we present a wearable TE power generator based on commercially available silk fabrics for energy harvesting from waste heat generated by the human body.Nanostructured Bi2Te3 and Sb2Te3 were synthesized hydrothermally and deposited on both sides of the silk fabric to form TE columns of n-type and p-type materials.After connecting the columns with silver foils,a prototype,integrating an array of 12 thermocouples was fabricated and evaluated as a wearable TE generator.The effects of repeated bending or twisting on the performance of the generator were examined.The practical applications of silk fabric-based TE generators with designed patterns for the collection of heat energy from the human body are demonstrated in this study.2.Fully-printed ultra-flexible supercapacitor supported by a single-textile substrateSilk fabrics were chosen as substrate materials to fabricate all-printed,single textile-supported supercapacitors with high performance,ultra-flexibility and great mechanical stability.The current collector and the active materials layers were screen-printed on a silk fabric and a polydimethylsiloxane(PDMS)film,respectively.After being pasted with gel electrolyte,the PDMSbased electrode was transferred exactly on top of the silk fabric-based one to obtain a single textilesupported supercapacitor,the design of which is inspired from the conventional sandwich-structured ones.Digital photographs and field-emission scanning electron micrographs were collected to illustrate the fabrication process.The electrochemical performance was evaluated with cyclic voltammetry(CV),galvanostatic charge-discharge(GCD)and electrochemical impedance spectroscopy(EIS).The mechanical stability and the compatibility of printing techniques to the textile aesthetics were also investigated to demonstrate the feasibility of the as-prepared devices in wearable electronics.3.Patterned fabrication of textile-based piezoresistive pressure sensor using Parafilm?Flexible pressure sensors can be applied to monitor human physiological parameters such as breath rate,pulse rate and respiration frequency.It is highly desirable to develop a facile and low-cost approach for the fabrication of textile-based pressure sensors with designed patterns.In the present work,a new technique involving cutting and melting of parafilm? is utilized to prepare a textile-based piezoresistive pressure sensor with two pieces of Ag nanowires-deposited silk fabrics as substrates.By simply cutting and melting of parafilm?,silk fabric-based pressure sensor with various patterns could be produced.Since the parafilm? also functions as the adhesive binder in the device,the melting temperature could significantly change the distance between two fabrics,further affecting the sensing performance.After investigation,it is found that the device incubated at 100 oC could deliver the best performance.The device also shows high sensitivity,rapid response and excellent stability(more than 500 loading/unloading cycles).The potential application of the sensor in human motion and physiological monitoring is demonstrated in this work.This study provides a facile and low-cost approach to fabricating textile-based flexible pressure sensors for practical wearable electronic applications.The success of this project is expected to introduce new approaches for the production of textilebased wearable electronic elements and to further expand the applications of silk fabrics.