| With the development of material science and electronic technology,wearable devices,such as flexible sensors,flexible energy storage devices and flexible power generators,have been widely used in personal communication,entertainment,health monitoring and portable energy supply.Because of its excellent wearability,skin affinity and compatibility with the conventional clothing industry,textile has been regarded as one of the ideal candidates to serve as the substrate of flexible electronic devices.Recently,great efforts have been dedicated to develop efficient methods for the rapid,large-area and low-cost preparation of textile-based flexible electronic systems.Screen printing technology is widely used to construct textile-based electronic devices due to its simple operation and low cost.However,the screen-printed material layer often shows a flat and compact surface morphology,which cannot meet the requirements of some devices on the surface microstructure.Moreover,water filtration,detergent exposure and mechanical distortion/friction usually occur in the washing process.Thus,it is also a grand challenge to enhance the washing tolerance of the textile-based electronic devices.In this project,flexible supercapacitor and flexible piezoresistive sensor were prepared with parafilm M?substrate using screen printing technology.The adhesive-removal properties of the devices were also tested to demonstrate the beauty of the parafilm M?substrate.The following aspects are included in this thesis:1.Screen-printing fabrication of material layer with micro-structured surfaceFullerene nanopowder,multi-walled carbon nanotubes and graphene oxide nanosheets were selected as the representatives of 0-D,1-D and 2-D nanomaterials,respectively,for the preparation of printing pastes.By adjusting the composition and proportion of the pastes,the surface morphology of the screen-printed material layer was examined with scanning electronic microscopy?SEM?.It is found that the surface structure of the screen-printing layer is highly correlated to the dimension of nanomaterials in the slurry.For the fullerene slurry,a smooth and compact surface can be obtained.The multi-walled carbon nanotube slurry could be utilized to produce ordered microstructure.As to two-dimensional graphene oxide slurry,the surface shows scaly structures.Further studies indicate that the density of the surface microstructure and the size of the micro-pillars can be effectively controlled by adjusting the mesh number.By changing the amount of binder,the inks with the mass ratio?materials:binder?of 5:1,15:1 and 25:1 were prepared to generate highly ordered micropillar arrays with the pillar height of 41.4±4.6?m.Based on the results,the possible mechanism for the screen-printing fabrication of microstructures was proposed.This work may provide a new method for controllable preparation of the printed electrode with microstructured surfaces.2.Parafilm M?-based re-stickable waterproof solid-state flexible supercapacitorsThis work uses screen printing technology to build a parafilm M?-based,waterproof all-solid-state flexible supercapacitor that can be repeatedly adhered-removed from the textile.Firstly,silver paste,carbon paste,and active materials were deposited on top of the parafilm?substrate by screen printing technology.Then,the device was directly packaged using the thermoplastic parafilm M?.Finally,the performance,flexibility,water resistance,and usability of the devices were tested.The results show that the supercapacitor has excellent capacitance performance(64 Fg-11 at a current density of 1 A g-1),high cycle stability?capacity retention rate after 2000 cycles is 88.6%?,and good flexibility?after bending/twisting 100 times the capacitance retention rate>98%?.Due to the superhydrophobic nature of parafilm M?,the capacitance of the prepared supercapacitor is maintained at 98.9%and 97.9%of its original level after 4 times of water rinses and 24 h of water immersion,respectively.More importantly,the device can be repeatedly attached and removed from textiles and the three in-series-connected devices can be attached on the T-shirt to power a LED lamp.This work not only reports a new type of waterproof,all-solid-state flexible supercapacitor,but also provides a new strategy for overcoming the problem of machine washing of textile electronics.3.Parafilm M?-based re-stickable flexible piezoresistive sensorPiezoresistive sensors have been extensively studied for their great flexibility and high sensitivity.Inspired by nature,constructing electrode with microstructured surfaces is one of the most effective ways to improve the sensing performance.In this work,screen printing was employed to prepare the parafilm?-based flexible electrodes with microstructured surface.Then,the electrodes were applied to build flexible piezoresistive sensors with parafilm M?as the substrate,the packaging material and the spacer.The multi-walled carbon nanotube slurry with different viscosities were prepared to screen-print electrodes for manufacturing piezoresistive devices.The results show that the surface microstructure can significantly improve the sensitivity of the devices.The sensor achieves the sensitivity ranging from 24.90 to 7.78 kPa-1?0-12 kPa?,and detection limit of 42 Pa.Parafilm M?-based sensor can be repeatedly adhered and removed from the textiles without significant damage to the device.It can also be attached on clothes to sense the human behaviors.This work not only develops a highly sensitive and re-stickable flexible piezoresistive sensor,but also expands the application of screen-printing technology in the field of flexible electronics.In this thesis,screen-printing technique was used to controllably prepare functional material layers with microstructured surface for the manufacture of flexible supercapacitor and highly sensitive piezoresistive sensor on parafilm M?.This work may provide a new method for large-area and low-cost fabrication of microstructured electrodes.The use of re-stickable thermoplastic may also be a new strategy to protect the textile-based flexible devices from machine washing. |
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