Controllable Fabrication Of Printed Microstructures And Its Application In Sensors

Flexible electronics are widely used in wearable electronics,haptic artificial intelligence,flexible displays,sensing and energy storage due to their easy conformability,high sensitivity and fast response.The overall performance of devices can be improved and their application scenarios expanded through strategies such as the development of sensitive functional materials,the design of functional layer microstructures and the optimisation of micro-and nanofabrication methods.Among these,one of the most effective ways to improve the performance of flexible devices is generally considered to be the innovative design of functional layer microstructures.The most commonly used methods for constructing microstructures are usually photolithography and natural template methods.However,they have some shortcomings in terms of process complexity and microstructure controllability.In response to the shortcomings of existing methods,this thesis proposes three printed microstructure controllable preparation methods that combine the design construction of microstructures with the selection of functional materials.Two different types of fully printed microstructured flexible pressure sensors are developed that achieve good sensing performance.The main research involves two areas:（1）the construction of microstructures and their sensing properties by sandpaper conformal printing and microcapsule assisted forming printing;（2）the construction of controllable microstructures and their sensing properties by 3D direct writing.The results of the thesis showed that:（1）For both sandpaper structures by conformal printing and porous structures by microcapsule assisted forming,the number of replicated sandpaper grains and the mass fraction of microcapsules have a significant effect on the morphology of the microstructure.The higher the sandpaper grit,the smaller and more numerous the microstructured films will be.As the mass fraction of microcapsules increases,the number of pores increases,but the expansion of the microcapsules is inhibited in some dense areas.Optimisation of ink formulations,addition of surfactants（0.5%）to spray inks and oxygen plasma treatment of the film surface can reduce the contact angle by a factor of 1and increase the surface energy by a factor of 5.The addition of polyvinylpyrrolidone（PVP）to the ink increases the stability of the microstructured conductive film.However,it reduces the conductivity by 5 orders of magnitude.The incorporation of microcapsules in functional inks increases the strain of the film by a factor of 0.65 under 3 MPa stress.By increasing the mass fraction of carbon material,the film resistance can be reduced by more than 500 times.The microstructured conductive films were applied to the sensor,optimisation of spray volume and sandpaper grit showed that:the highest film sensitivity of 53.33 kPa^-1was achieved with 0.0125 mg/cm² of spraying,replicating 80 grit sandpaper.（2）The rheology and microstructure of 3D inks are significantly affected by the resin/carbon black ratio.The higher the proportion of polydimethylsiloxane（PDMS）and carbon black in model SE1700,the higher the viscosity of the ink and the less flattening of the printed structure.However,when the proportion of carbon black exceeds 5%,ink extrusion becomes difficult.With a small preset line spacing during printing,the dense surface of the printed structure will have a low bump and be less prone to deformation.Both the construction of microstructures and the incorporation of conductive carbon black improve sensor performance.Sensors with microstructures are 0.7 times more sensitive than those with little or no microstructure,and sensors with carbon black combined with microstructures are 10 times more sensitive.