Pressure-temperature Dual-parameter Flexible Sensor Based On Conformal Printing Of PEDOT Microstructures

With the vigorous development of artificial intelligence,Internet of Things,wearable electronics and other technologies,flexible pressure sensors,as one of the key basic components,are widely used due to their broad application prospects in the fields of human-computer interaction,medical health,electronic skin,and perception reconstruction.However,flexible pressure sensors still face the technical bottleneck that the sensing function is single,and the traditional micro-nano processing methods cannot meet the requirements of large-area and mass-manufacturing devices.Aiming at the above technical bottlenecks,this thesis proposes a research idea to construct a pressure-temperature dual-parameter flexible sensor by conformal printing of poly-3,4-ethylenedioxythiophene/polystyrene sulfonic acid（PEDOT:PSS）functional ink interface.The specific scheme is as follows:first,a PEDOT:PSS-based functional ink suitable for screen printing is prepared;next,PEDOT is conformally constructed on the surface of a polydimethylsiloxane（PDMS）film with a multi-level microstructure by screen printing PEDOT:PSS conductive coating;finally,the above-mentioned PEDOT:PSS-based microstructured functional film was encapsulated with interdigital electrodes,the interface multi-level microstructure was used to realize the change of contact resistance under pressure stimulation,and the thermoelectric properties of PEDOT:PSS were used to realize the temperature change.sensing.The main research contents of the thesis include three aspects:（1）Research on screen printing sensing functional ink based on PEDOT:PSS;（2）Research on conformal printing construction of PEDOT:PSS based sensing functional layer and its structure-activity relationship;（3）Model design and exploration of the pressure-temperature dual-parameter sensor model.The results of the thesis found:（1）Waterborne polyurethane（PU）can effectively improve the interfacial bonding strength between the printed PEDOT:PSS coating and the PDMS film.When the PU addition amount was 60 wt.%,the PEDOT:PSS/microstructured PDMS interface could withstand 100 KPa pressure without damage.After adding 0.3 wt.%tackifier and 0.25wt.%surfactant（FS-30）,the viscosity of PEDOT:PSS-based functional ink increased from 0.5 Pa·s to 1 Pa·s,and the surface tension decreased from 58 m N/m to 23m N/m,which meets the printability of screen printing inks.Oxygen plasma was used to treat the surface of PDMS film,and its surface energy was increased from 39m N/m to 64m N/m,which reduced the contact angle of PEDOT:PSS functional ink on its surface from 110°to 25°.The well-controlled wetting and spreading behavior of the microstructured PDMS surface lays the foundation for the subsequent conformal printing of conductive layers.（2）Increasing the number of printings can effectively improve the conformal effect of PEDOT:PSS functional ink on the surface of microstructured PDMS.When printed once,the PEDOT:PSS coating has a large resistance,about 2MΩ.Printing three times reduces the PEDOT:PSS coating resistance to about 1.5KΩ.Through micro-morphological analysis,it is found that the use of printing can realize the conformality of the ink on the surface of the multi-level structure.The data of EDS shows that the ink has a relatively good distribution on the surface of the structure within the printing range,but the distribution of the ink is affected by the scale of the multi-level structure.The influence of the ink distribution structure top to the bottom of the structure content will increase.This proves that the PEDOT:PSS functional ink achieves good conformality on the microstructured PDMS surface.（3）The obtained microstructured sensing functional layer film was packaged and tested with the cross-finger electrode.When the microstructure was replicated with 80mesh sand thesis,the multistage structure had a wide longitudinal deformation space,and the sensor had a wide linear pressure response range,in 0-350kpa pressure range with a sensitivity of 32Kpa^-1.When using 3000 mesh sandpaper for microstructural replication,the longitudinal space of multistage structure is narrow,and the sensor is rapidly saturated in 0-30kpa pressure range with a sensitivity of 134.25Kpa^-1.When it is larger than 30KPa,the spatial deformation is saturated with a sensitivity of 10.15Kpa^-1.（4）Dimethyl sulfoxide（DMSO）was used to doping PEDOT:PSS film to improve its electrical conductivity and effectively eliminate the influence of temperature on the resistance of PEDOT:PSS film.Temperature has little effect on the resistance of PEDOT:PSS film in the temperature range of 10℃～90℃.By printing silver electrode at both ends of the film and forming thermoelectric junction with PEDOT:PSS,the temperature difference generated by the electrode temperature difference is detected to realize the sensing detection of temperature.The Seebeck coefficient of PEDOT:PSS film is about22.3μV/K.The temperature sensing can be realized by rational design of sensing model based on the thermoelectric characteristics of PEOT:PSS film.In this thesis,a pressure-temperature dual-parameter flexible sensor is constructed by conformal screen printing of PEDOT:PSS-based functional ink,which overcomes the technical bottleneck of complex structure design and easy signal crosstalk of traditional multi-parameter flexible sensors.The integrated printing and additive manufacturing technology used in this thesis is conducive to the realization of large-area and batch production of flexible sensors,which is of great significance for consolidating the basic theory in this field,guiding the development of highly sensitive functional materials,and promoting the upgrading of manufacturing technology.