Preparation And Performance Of Flexible Electronic Devices Based On Degradable Elastomers

The development of green and environmentally friendly flexible electronic devices based on degradable materials is of great significance for the healthy and sustainable development of wearable technology.Although various degradable materials have been explored for green wearable electronics,the synthesis of degradable elastomers with integrated characteristics of low modulus,self-adhesion,high resilience,and low hysteresis remains challenging.In this thesis,a biodegradable poly（citrate-1,8-octanediol-caprolactone）（POCL）elastomer was prepared via condensation polymerization.Biodegradable strain sensors and stretchable electroluminescent devices（ACEL）were prepared by blending POCL with functional materials.The relationship between the molecular structures and mechanical properties,transparency,wettability,degradation,and other properties was investigated.The electrical performance and responsibilities of the strain sensors and the luminescence performance of the ACEL devices were explored.The main research work and results are as follows:The biodegradable polymer POCL was prepared by using anhydrous citric acid,1,8-octanol and PCL as raw materials.It was found that POCL was elastomer when the PCL content was 0-60%;while POCL became a plastic material when the PCL content was higher than 60%,due to the crystallization of PCL segments.The structural analysis showed that the POCL elastomer had a loosely cross-linked network,which contained a large number of tangled flexible chains.Since the molecular chain was amorphous,the POCL elastomers showed high transparency with transmittance higher than 88.5%.With the increase of PCL content,the gel content and crosslinking density decreased,the elongation at break gradually increased,the elastic modulus decreased,and the hydrophilicity decreased.In addition,the POCL elastomers presented high resilience,and their average tensile recovery rate reached 95%.Due to the synergistic effect of chemical cross-links and physical entanglements,the POCL elastomers possessed low modulus and high elasticity and also exhibited low hysteresis.The ratio of the dissipated energy to the applied work was about 3.2%～6.6%.In vitro degradation experiments showed that the POCL elastomer degraded faster in the PBS buffers with higher p H values,and the higher content of PCL,the faster degradation at all p H values.Based on the crystallization,mechanical properties,and transparency of the POCL prepolymers and elastomers with different PCL contents,the elastomer with 50%PCL content(POCL_0.5)turned out to show the best performance,so POCL_0.5was selected for the preparation of flexible electronic devices.Strain sensors were prepared by blending POCL_0.5 elastomer with ionic liquids（IL）.The conductivity of POCL_0.5/IL ionogel increased with the increase of IL contents.When the content of IL reaches 50 wt%,the ionogel has the best transparency and conductivity,and can be applied as strain sensors.After 50 tensile-recovery cycles,the strain sensor maintained a high recovery rate of nearly 100%,and the ratio of the dissipated energy to the applied work was about 6.2%,showing a good low hysteresis.The sensors showed good strain response and sensitivity under different strain rates.In addition,after 15600 tests,the sensor retained a reproducible response,showing high fatigue resistance.In addition to excellent mechanical properties and response performance,the strain sensors also exhibited self-adhesion;the peeling force on human skin was around 25 N/m.When a piece of ionogel was attached to human skin without any interface glue,it wrinkled conformally with the human skin.The inorganic Zn S:Cu powder was uniformly dispersed in POCL prepolymer.By thermal curing of the blends,the dielectric POCL/Zn S:Cu luminescent layer was obtained.The electroluminescent device was composed of the luminescent layer sandwiched between a pair of transparent POCL_0.5/IL_0.5 ionogel.The ACEL devices can stably emit blue light under various deformation modes such as folding,twisting and stretching,showing excellent flexibility.The ACEL device was dissolved in a PBS buffer（p H=9）within 21 weeks.After the elastomers were resolved,inorganic Zn S:Cu powders could be collected for recycling.