| Sensors,human tools for obtaining information from natural environment,have always played an important role in production and life.With the continuous development of emerging fields such as medical health,electronic skin,soft robots and artificial intelligence,traditional rigid sensors cannot meet the needs of the time,and flexible sensors are attracting more and more attention.As the core of flexible sensors,the flexible sensing materials are the fundamental factors that determine the performance of the sensors.Therefore,developing new high-performance flexible sensing materials is one of the main ways to promote flexible sensor development.As materials science continues to develop,a wide range of nanomaterials have been created in recent years,particularly two-dimensional.MXenes are a new type of twodimensional carbon and/or nitride,which have rich and controllable physical and chemical properties and surface functional groups,and show sufficient application prospects in the field of flexible sensing.However,the application of pristine MXenes materials in the field of sensing is limited to some extent by the low sensitivity and inadequate mechanical properties of MXenes materials themselves.Considering the above-mentioned deficiencies,this dissertation takes the development of new flexible sensors as the research objective,selects the traditional sensing material and the new2 D MXene as the research subject,gives full play to the coordination between them,prepares a series of polymer/MXene flexible sensing materials,and systematically investigates their flexible sensing performance and use.The main research contents are as follows:(1)The preparation of polyaniline/MXene nanocomposites and studies of their flexible gas-sensing properties.PANI/MXene nanocomposites were prepared by synthesising polyaniline nanoparticles on multilayer bulk MXene using lowtemperature in-situ polymerization.The morphology,structure and composition of PANI/MXene were investigated by physical characterization.It was proved that polyaniline nanoparticles with an average diameter of 25 nm were uniformly distributed on the layered structure of MXene.The gas-sensing properties of PANI/MXene were studied by electrochemical characterization.It not only has a response of 41.1% to 200 ppm ethanol,but also has a fast response/recovery time(0.4/0.5 seconds),high cycle stability and flexibility.The sensing mechanism of PANI/MXene was studied by DFT simulation,indicating the outstanding role of surface functional groups in gas-sensing.(2)The preparation of polyvinyl alcohol/MXene electronic skin and studies of its flexible pressure-sensing properties.The PVA/MXene electronic skin was prepared by vacuum-assisted filtration of a mixed solution of MXene and polyvinyl alcohol.Thanks to the synergistic incorporation of strong hydrogen bonds in MXene and PVA,the effective layer spacing and mechanical flexibility of this electronic skin are significantly improved over pristine MXene film.As a result,the PVA/MXene electronic skin is capable of rapid dynamic pressure detection over a wide range of 0 to100 k Pa,while maintaining stable performance over 7,000 cycles of long-term continuous operation.Excellent environmental stability of PVA/MXene electronic skin demonstrated by molecular dynamics simulation.Therefore,the high stability of morphology and pressure-sensing properties can be maintained even after long-term immersion in various p H solutions.Finally,through in vitro cell culture and detection of visceral activity in mice,the biocompatibility and practicality of the PVA/MXene electronic skin was demonstrated.(3)The preparation of sodium alginate coated MXene film and studies of its temperature-sensing properties.To produce paper-like ultra-flexible sodium alginate coated MXene film,MXene@starch mixed solution treated with yeast was fully soaked in sodium alginate and calcium chloride solution.The system exhibits excellent temperature sensing performance over the full temperature range of-20 ℃ to 100 ℃using MXene as the active conductive skeleton and sodium alginate hydrogel as the heat-sensitive coating layer.The high sensitivity of the sodium alginate coated MXene film makes it possible to detect the temperature of approaching objects.In the end,the temperature monitoring system based on the film has successfully realized the monitoring of the operating temperature of the cold storage model.(4)The preparation of Poly(acrylic acid-acrylamide)/MXene@PDADMAC semiinterpenetrating hydrogels and studies of their strain-sensing properties.P(AA-coAM)/MXene@PDADMAC semi-interpenetrating hydrogels have been synthesized by heating copolymerization of AA(acrylic acid)and AM(acrylamide)monomers with MXene@PDADMAC as template,APS(ammonium persulfate)as initiator and MXene nanoflakes as cross-linking agent,conductive filler.The hydrogel exhibits excellent mechanical properties and low hysteresis in mechanical property tests due to its stable network structure.As a result,it exhibits sensitive response characteristics in the strain range of 0-300%,with a sensitivity of up to 0.98.At the same time,the significantly improved water retention of the hydrogels was explained by the formation of a large number of hydrogen bonds with water molecules using DFT simulations,LF-NMR,FTIR and other characterizations.As a result,it has maintained stable performance in the 30-day long-term test and 1100 cycle tests.Finally,the hydrogel-based portable sign language-Chinese character conversion device can realize real-time sign language translation and display,thanks to its high sensitivity and good fit with fingers.In this dissertation,a series of polymer/MXene composites have been prepared and their properties for flexible sensing have been systematically investigated.With the improvement of the preparation methods of MXene materials,the adjustment of the types of polymers and the composite methods,the polymer/MXene flexible sensing system has been continuously improved,and the development of MXene-based flexible sensors has been promoted. |
