Design And Application Of Flexible Functional Polymer Materials And Devices

Recently,extensive researches about flexible devices have been carried out on biomedicine,energy storage and conversion,flexible wearable device and other fields,due to its flexible and lightweight features.Flexible devices mostly adopt flexible electronic technology.Rigid microelectronic units are located on flexible substrate and connected through flexible conductive interconnectors.The rigid microelectronic units largely limit device's deformation degree,and the process is complex,not suitable for large-scale assembly.Utilizing the organic conductive materials and semiconductors with intrinsic stretchability to fabricate flexible device is a simple and effective way.But this kind of materials' stretchability is poor,and their mechnical and electrical properties need to be improved.In this dissertation,flexible functional polymer materials have been designed and chosen to directly fabricate flexible devices,such as flexible supercapacitors,flexible actuators,and flexible pyroelectric nanogenerator.We studied the flexible devices'applications in energy storage,harvest and conversion area.This dissertation provides fresh insights into designing flexible conducting polymers and further fabricating flexible devices.The work includes the following four parts:(1)Polypyrrole(PPy)can be prepared by electrochemical polymerization to form a self-standing film.Due to its conjugated chain structure,conventional PPy films are brittle,which limits its application in flexible electronics.Many jobs have been carried out to improve the mechanical property and conductivity.But the strength and stretchability of PPy films are still low.How to successfully synthesize strong,ductile,and highly conductive PPy is the key point for its application in flexible electronics.Inspired by the network structure of animal dermis,we have designed and synthesized a series of polyol-polypyrrole(polyol-PPy)composites.Polyols and PPy are cross-linked by hydrogen bonding and electrostatic interactions to form a dynamic network,which helps to dissipate destructive energy efficiently and largely improve materials' strength and toughness.Among these polyols,the tetra-armed polyethylene glycol(PEE)provides the best performance.The PEE-PPy film shows both high tensile strength(125 MPa)and high flexibility(elongation-at-break-75%),leading to high tensile toughness(73 MJ/m~3)that exceeds the value of cocoon silk(70 MJ/m~3).In addition,the PEE-PPy film also shows a high conductivity(115 S/cm).These superior properties enable polyol-PPy composites as potential electronic materials for making flexible electronics.(2)The polyol-PPy film prepared in the first section is a water responsive polymer.In this section,we fabricate a moisture-driven mini-tractor by incorporating superparamagnetic nanoparticles into water-responsive PPy films.Under the direction of a static magnetic field,the mini-tractor directly prepared by flexible polymer film can harvest energy from moisture and quickly transport cargo that is 5-times heavier than itself to the destination.(3)With the development of wearable and flexible electronics devices,flexible supercapacitors(SCs)have been designed for power supply.The PPy doped with PEG 600 owned superior mechanical and electrochemical properties,which can be used as electrode material and current collector simultaneously.Thus,we fabricated a flexible self-freestanding SC with PEG 600-PPy film directly.This SC provides a large capacitance(561 F/cm~3)and has good cycle stability and long life.The device is ultrathin with a whole thickness of 100 ?m.And the device can be deformed such as folding and bending,with its capacitor performance remaining stable.This flexible SC directly fabricated by conductive polypyrrole with high performance can be used as energy storage devices for ultrathin flexible electronic devices.(4)Energy harvesting via pyroelectric nanogenerators(PNGs)is emerging as an attractive way to utilize waste heat.However,most of current PNGs need mechanical or electrical alternating devices to achieve fast temperature oscillation,which is the key for PNGs to work.We designed a self-sustaining pyroelectric generator based on commercial polyvinylidene difluoride polymer simply driven by hot water vapor,without any energy-consuming alternating devices.The PNG can effectively harvest waste heat in the environment and was able to output an open-circuit voltage of 145 V Our PNG could provide uninterrupted electricity to drive low-power electronic devices(such as a digital watch)to work continuously and light LED.This self-sustaining flexible generator is expected to be used as flexible energy supply device and provides a new strategy for efficiently recovering energy from hot water vapor that is wasted in industry and in our daily life.