Research On Controllable Manufacturing Process Of Hierarchical Microstructure Array For Flexible Strain Sensor

With the development of intelligent materials and micro/nano structure manufacturing technologies,the limitations of traditional rigid sensors become more and more obvious,and flexible strain sensors are increasingly prominent in health monitoring,electronic skin,humancomputer interaction,soft robots and other fields.Flexible strain sensors are the key components of wearable electronic products.Sensitivity and sensing range are the leading performance indexes of flexible strain sensors,and construct micro-nano hierarchical structure is an effective strategy to improve the performance of flexible strain sensors.Combined with the commonly used micro/nano hierarchical structure manufacturing methods,a composite forming process of micro-nanoimprinting and buckling was proposed to efficiently build primary V-groove array based on micro-nanoimprinting and curved secondary wrinkle structure based on buckling instability.In this paper,systematic research is carried out from the three aspects of "microstructure array process experiment,simulation analysis and theoretical modeling",focusing on the key issues which contains the efficient and controllable manufacturing of micro-nano hierarchical structure and the preparation and application of flexible strain sensors.According to the requirements of flexible strain sensor for efficient and controllable manufacturing of micro-nano hierarchical structural arrays,the V-groove array is selected as the first-level structure,and the forming process law and forming mechanism of the hierarchical structural arrays were explored,so as to lay the foundation for the efficient and controllable manufacturing of micro-nano hierarchical structure.Firstly,the uniaxial pre-stretching process is investigated,and the effects of first-level microstructure,substrate thickness and pre-strain on the forming results are analyzed through single factor experiments.On this basis,the response surface of each parameter is established through Box-Behnken experiments,and the coupling effects of each process parameter are analyzed to obtain the optimal forming process window.To further reveal the forming mechanism of buckling destabilization process,a process simulation model is established to accurately simulate the nonlinear buckling process and analyze the influence of different process parameters on the forming results,so as to provide theoretical guidance for the controllable manufacturing of micro-nano hierarchical structure arrays.The biaxial pre-stretching process is investigated to explore the influence of pre-strain loading and release strategies on the formation of the hierarchical structure morphology.Firstly,a biaxial stretching experimental bench is built with the characteristics of soft materials,and a special fixture for soft substrates is designed to realize the accurate application and release of biaxial strain.The effects of biaxial isometric and non-isometric pre-strain application and releasing strategies on the forming results are analyzed by single-factor experiments to further extend the forming laws of complex hierarchical structural morphology.A theoretical model for the controllable forming of wrinkle secondary structure with buckling instability is established to guide the controlled forming of micro-nano hierarchical structures.Firstly,for the planar substrate,the wrinkle critical buckling instability mode is explored based on the static equilibrium method,and then the amplitude variation law of buckling is obtained by the energy method and further extended to the large deformation case.A theoretical model is established for the structured substrate buckling instability,and the influence of each process parameter on the forming results is analyzed.A finite element simulation model is established to obtain the critical instability mode of the curved substrate wrinkles,which provides a theoretical basis for the controlled forming of micro-nano hierarchical structures.Based on the prepared micro hierarchical structures,further research on the fabrication of high-performance flexible strain sensors is carried out.High performance flexible strain sensors with unidirectional sensing and anisotropic sensing are constructed based on uniaxial and biaxial pre-stretching processes,respectively.Firstly,the sensing performance of micro-nano hierarchical structures with different morphologies are compared to analyze the influence of microstructure morphology on the sensing performance.By observing the morphological changes under different strains,the sensing mechanism of the sensor is analyzed to provide theoretical guidance for the construction of high-performance sensor devices,and then the dynamic performance of the sensor is characterized and applied to the monitoring of human motion and physiological signals.