The Application Of 3D Direct Write Technique And Smart Responsive Film In Energy Conversion

With the exhaustion of traditional energy sources and the aggravation of environmental pollution,it has become an important way to realize sustainable development by developing environment-friendly energy conversion technologies.As a new nano-device,nanogenerators have realized the conversion of mechanical energy into electrical energy,which has become a hot spot in energy conversion in recent years.It has been predicted that nanogenerators based on helical micro-nano structures have a higher output voltage,however,there are great challenges in preparation of helical structure in micro/nano scale.Low-grade waste heat also contains huge energy.Converting low-grade waste heat into electricity is an attractive method to alleviate the growing energy crisis.However,the waste heat below 100 °C,especially near room temperature,has a low energy level,making it difficult to recycle.Besides,energy conversion is not limited to the collection of electrical energy.Developing multiresponsive system and converting external stimuli directly into mechanical motion without electrical source are also a way to alleviate energy crisis.This thesis focuses on energy conversion.Firstly,a new 3D direct-write method is developed to prepare polymer helical nanobelt.A piezoelectric nanogenerator based on helical PVDF-Tr FE nanobelt is prepared by using the 3D direct-write method.Finally,the liquid crystal network(LCN)is used as the response material for the collection of low-grade waste heat below 100 °C and multiresponsive actuators.The main research content of this thesis are as follows:(1)We developed a very simple direct write technique for preparing helical nanobelts.The formation of the helical nanobelt was mainly due to the geometric asymmetry of the polymer and the inner/outer surface strain difference.The influences of the size of the nozzle and the pulling speed on the shape of the helical nanobelt were investigated.The 3D direct-write method proposed in this paper was proved to be a general method for the preparation of polymer helical nanobelts.A displacement sensor based on polypyrrole helical nanobelt has been investigated.The resolution of the displacement sensor was 300 nm.This displacement sensor showed a linear response to the displacement change in the tested range of 300 nm to 7.2 μm.(2)A piezoelectric nanogenerator based on helical carbon materials(graphene and multi-walled carbon nanotube)and PVDF-Tr FE hybrid nanobelts was prepared by using the 3D direct-write method proposed in this paper.Due to the geometric stress constraint effect,helical PVDF-Tr FE nanobelts have a higher piezoelectric coefficient than their thin films.The addition of carbon materials could enhance the piezoelectric performance of the helical PVDF-Tr FE nanobelt.The hybrid helical nanobelt containing 0.005 wt.% graphene had the highest output voltage of 35 m V.This work demonstrates that the helical structures are able to improve the performance of piezoelectric nanogenerators,which provides a way for the design of self-powered micro-electronic devices.(3)A PVDF-Tr FE/LCN bilayer actuator was successfully prepared to recover the low-grade waste heat.The actuator utilized the thermal expansion property of LCN and mechanical tension to maintain automotion of the whole device.This dynamic generator was able to operate in a temperature of ～30 ℃ with a temperature difference of 6 K.The device was found to exhibit a maximum output voltage of ～4.5 m V.This work extends the versatility of LCN and actuators,and provides more options for lowgrade waste heat recovery near room temperature.(4)A multiresponsive actuator based on polyimide(PI)and an azobenzene contained liquid crystal network(azo-LCN)was designed to response to humidity,organic solvent vapor and light.After the bilayer film being activated by alkaline solution,the motion of self-oscillation and crawling as well as an artificial gripper controlled by light and solvent vapors could be realized.In addition,a unique dual-functional information storage was also realized by the photoisomerization of azo molecules and the phase transition of azo-LCN.