| Through the measurement of body surface pressure,real-time monitoring of human health and limb movements and other behaviors,which is a hot research and development in the wearable field.Conductive filler was compounded with porous flexible polymer,and formed conductive polymer composites.When the conductive polymer composites were subjected to external stresses,the change of contact point between fillers causeed the regular response of resistivity and produced piezoresistive effect.This kind of piezoresistive material was becoming the key to construct intelligent and functional wearable devices.However,at present,the commercial porous polymer foam has an aperture of more than 150?m.The low specific surface area of the material limits the density of the potential contacts between the packings,so it can not be used to prepare sensors with high sensitivity and wide range of power.In this project,Pickering high internal emulsion?Pickering-HIPE?was prepared by using polyurethane?PU?water dispersions as the continuous phase and cyclohexane as the dispersed phase.In the emulsion,PU elastic particles stabilized cyclohexane droplets were used as liquid templates,and freeze dried technology was used to remove the template.PU particles were formed and formed flexible PU foam materials with small pore size.After that,the foam material was used as the framework and the flexible conductive PU composite foam?rGO@PU sensor?was prepared by means of"soaked graphene oxide dispersion?GO?-VC reduction"method.Research shows:?1?Even if adding sodium chloride?NaCl?in continuous phase or using PU/SDS or PU/Tween-20 composite stabilized system,the diameter of PU foam material which was freeze-dried was greatly deviating from the emulsion particle size before freeze-drying,so it was difficult to control the foam aperture quantitatively.?2?"Ostwald"ripening was the main reason for the instability of Pickering-HIPE and the particle size incontrollable of foam materials.By adding HD in the dispersed phase and inhibiting the"austenite"ripening of the emulsion,the PU foam material with complete pore structure was obtained.The pore size of the foam was basically coincided with the particle size of the emulsion.The minimum average pore diameter of the material was about 32?m,which was only about 1/5 of the commercial foam.?3?By adjusting the solid content of PU water dispersions or the"oil/water"ratio of HIPE,the average pore size of flexible PU foams can be controlled within the range of 30-200?m.?4?when changing the size of GO lamination and the number of times of immersion,the rGO coverage of the PU foam composite material would also change,and caused the change of piezoresistive sensitivity and stress path.After 3 times in GO dispersion solution of small layer size,the stress sensitivity of the rGO@PU sensor was 0.31kPa-1,and the maximum stress was389kPa.?5?The material could be used to detect compression,distortion,bending and other multi-dimensional stresses.The bending range ccould reach 360°,the resolution was 1.26°,and the maximum torsion angle is 114 rad/m. |
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