Preparation Of Piezo-Sensor Based On Monolayer MoS₂ And Its Application On Textiles

As an intelligent device capable of converting mechanical deformation into regular voltage signals,flexible piezoelectric sensors have shown great application prospects in the fields of medical health,electronic skin,and human motion detection.However,the present flexible piezoelectric sensors still have certain shortages in the aspects of responsiveness and flexibility,which are difficult to satisfy the wearable needs of people in daily life.Therefore,the development of flexible composites with excellent piezoelectric properties for the comprehensive performance of piezoelectric sensors is important for the study of their applications in wearable textile articles.Monolayer MoS₂has exceptional piezoelectric responsiveness and has the advantages of smaller size and higher energy,which is often used in the design of a new generation of nano-pressure sensor devices.However,it is still worth to be explored in achieving the uniform preparation of small-sized monolayer MoS₂ crystals.In this paper,the electrostatic spinning and high-temperature calcination techniques were used to construct a carbon nanofiber loading substrate and realize the controlled preparation of monolayer MoS₂ carbon nanofibers（MoS₂-CNFs）,and investigate the structure and electrical properties of MoS₂-CNFs;furthermore,a flexible PVDF-based piezoelectric composite was designed and prepared based on monolayer MoS₂-CNFs,and the piezoelectric properties were tested and evaluated.Finally,a flexible piezoelectric sensor was fabricated as a substrate to detect the pressure signals generated by human physiological movements（breathing,pulse,finger bending）.（1）The high-temperature calcination technique was used to carbonize nanofibers to construct a loading substrate to achieve the modulation of the MoS₂ microcrystalline structure inside carbon fibers.The effects of sulfur source deposition,preliminary decomposition temperature,calcination time,and temperature increase rate on the internal MoS₂ structure and properties of carbon fibers were investigated.The MoS₂microcrystal structure was characterized by SEM,TEM,XRD,Raman,XPS,and four-probe methods,and the results showed that the precursor film（PANNAMo）was pyrolyzed at an initial decomposition temperature of 400℃,a calcination temperature of1100℃,and a ramp rate of 2℃/min to achieve small and medium-sized,monolayer structured MoS₂ nanocrystals in the carbon fiber matrix The homogeneous preparation of MoS₂ nanocrystals on the carbon fiber matrix was achieved.The piezoelectric sensor of MoS₂-CNFs was constructed on this foundation,and the results showed that the output voltage amplitude could reach 850 m V with deformation,which proved that the prepared MoS₂-CNFs have good piezoelectric properties.（2）MoS₂-CNFs were broken to produce MoS₂ carbon nanofiber rods（MoS₂-CNRs）for the preparation of MoS₂-CNRs/PVDF piezoelectric composites.The effects of MoS₂-CNRs content were investigated on the phase structure,thermal properties,mechanical properties,and piezoelectric constants of PVDF.The results showed that the total relative content of PVDF-βandγphases in the produced composite films was increased from69.93%to 89.48%and the piezoelectric constants were increased from 14.8 p C/N to 21.4p C/N at a MoS₂-CNRs content of 1.5%（relative to the mass of PVDF）,which proved that the addition of MoS₂-CNRs could effectively induce theα-crystalline toβ-crystalline transition in PVDF crystallization and improve the piezoelectric properties.Further,the MoS₂-CNRs were mechanically ball-milled using polyvinylpyrrolidone（PVP）as a dispersant to produce MoS₂ carbon nanoparticles（MoS₂-CNRs）,which were used to prepare MoS₂-CNRs/PVDF piezoelectric composites as functional fillers.After the modification of MoS₂-CNCs by PVP,the average particle size was reduced to about 300nm and the PDI was 0.178,which improve its dispersion in the system;Moreover,the PVDF-βphase content in the composite film was further enhanced after PVP modification,and the piezoelectric constant was increased from 14.8 p C/N to 34.0 p C/N in the pure PVDF film,indicating that the MoS₂-CNCs in uniform dispersion in PVDF nanofibers can effectively enhance the piezoelectric properties of the composites.（3）The MoS₂-CNFs-based flexible piezoelectric sensors were designed and prepared by encapsulating the above-mentioned composite films and tested for voltage output performance.The experiments show that the maximum voltage output amplitude of the flexible piezoelectric sensor with an area size of 2×2 cm² and thickness of 0.985mm can be 2.12 V and keep good linearity with R²=0.92715 in the pressure interval of0.05～0.5N.Through the voltage signal acquisition of the exhaled breath,it is shown that the voltage peak of the flexible sensor based on MoS₂-CNFs can be increased from 150m V of pure The results to 450 m V.It is shown that the piezoelectric composite material based on monolayer MoS₂-CNFs can detect the pressure signal during finger bending,pulse beating,and breathing after being attached to the fabric.