| Flexible electronic materials with both flexibility and electronic properties have broad applications in the areas of wearable technology,flexible robots,and transducers.The dielectric elastomer and the flexible conductor both belong to the flexible electronic system.The one of traditional methods to study these materials is to introduce rigid particles into the elastomer matrix to increase the electrical properties.However,the incompatibility between inherent rigidity of the inorganic filler and the flexibility of elastomer matrix may cause stress concentration,increase of stiffness,decrease of ductility,and limit the durability of the material in its mechanical response.There are few studies on stretchable conductive materials with high electrical conductivity and high mechanical flexibility.Similarly,high dielectric constants,low elastic modulus,and low dielectric loss of dielectric elastomer materials are difficult to achieve at the same time,which limits the material application.This work used flowable liquid metal and silicone rubber to prepare functional flexible materials.In this research,two aspects of works are mainly included as follows:1)A three-dimensional polyurethane sponge(PUS)was filled with liquid flowable liquid metal(Galinstan)at room temperature and then compounded with silicone rubber(PDMS)to prepare a stretchable highly conductive elastomer composite.The three-dimensional open cell structure of PUS can store and support the liquid metal,and provide the skeleton of the conductive network.Galinstan's mobility ensures the continuation of the conductive network in the process of deformation.The loading of the liquid metal was controlled by controlling the evacuation time in the experiment and the effect of the liquid metal loading on the conductivity of the PUS-Galinstan composite was also investigated.In the range of evacuation time from 5 to 60 minutes,the longer time resulted in greater loading of liquid metal,and higher conductivity,and the highest conductivity is 2.67×106 S/m.At the same time,the experiment explored the electromechanical stability of the material:such as PUS-Galinstan composite with a density of 4.34 g/cm3,the conductivity is 1.89×106 S/m,when the maximum tensile strain was 275%,the change in electrical resistance(?R/R0)was 433%.After the combination of PUS-Galinstan and PDMS,the mechanical properties of the material have been further improved:the tensile strength was 1.11 MPa,the elongation at break reached 419%,and the modulus of elasticity was 0.22 MPa.Besides,the material has good conductivity and electromechanical stability,electrical conductivity is 1.87×106 S/m and a?R/R0 of 453%at 250%strain.2)Firstly,liquid metal nano-droplet(LM-NP)was prepared by ultrasonic technology,and a flexible silicone rubber dielectric elastomer composite was prepared based on LM-NP.Ultrasonic dispersion was first used to compare the effects of adding 3-mercaptopropyltriethoxysilane(KH580)or without KH580 on the dispersion of liquid metal.The hydrazine group in KH580 was bonded with liquid metal and a self-assembled film was formed with a thickness of about 6 nm on the surface to prevent re-melting of the dispersed liquid metal.The average size of the liquid metal particles reached 193 nm,about 88.6%of the liquid metal nanoparticle size was below 100 nm,and the liquid metal emulsion after ultrasonication can be stable for 48 hours with no significant sedimentation,while the average particle size of the liquid metal without KH580 is about 1 ?m,and it settles after 3 hours,thus affirming that the KH580 is helpful for the stability of LM-NP.LM-NP/PDMS composites have high dielectric constant,low dielectric loss and low modulus.When the volume fraction of the liquid metal is 63%,the dielectric constant of the composite reached to 25,which is 625%higher than that of the pure DC3481 silicone rubber,and within the frequency range of 10-1 to 106Hz,the loss tangent is always less than 0.2 and the elastic modulus is 0.91 MPa. |
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