Preparation And Application Of Flexible Piezoresistive Sensing Layer Based On Hierarchical Porous Structur

Flexible force-sensitive sensors have attracted extensive attention due to their potential applications in the fields of human physiological signal monitoring,robotics and electronic skin.It is soft,comfortable,and easy to fit the skin.Besides,it can convert external stimulation into electrical signal or other signal output and detect the magnitude of the external force more accurately.In this paper,the research progress of flexible force-sensitive sensors for porous structure-sensitive materials is reviewed.The research field of porous structure flexible force-sensitive sensors is classified,and the characteristics,preparation methods and application fields are studied in detail.It is concluded that the graded porous sensors with different parameters is the main direction of this development.In view of the fact that most flexible force-sensitive sensors cannot possess both high sensitivity and wide detection range.Besides,they have poor air and moisture permeability when worn on the surface of skin.Thus,a flexible force-sensitive layer and its sensor with graded porous structure are proposed in this paper.The sensor has high sensitivity,wide detection range,good air moisture permeability,and good moisture permeability.In this paper,a convenient non-solvent induced phase separation（NIPS）method was used to prepare a flexible sensor layer based on graded porous structure.Using deionized water as non-solvent,different mass fractions of polyurethane homogeneous solutions（10%,12%,14%,16%）were layered into non-solvent to construct grade porous polyurethane membranes 10%PU,10%12%PU,10%14%PU,10%16%PU with grading 0,2,4,6.Then one-dimensional carbon nanotubes（CNT）and two-dimensional MXene were dispersed on grade porous membranes by ultrasonic method,and graded porous polyurethane membranes called10%PU@MXene+CNT,10%12%PU@MXene+CNT,10%14%PU@MXene+CNT,10%16%PU@MXene+CNT with multi-dimensional conductive paths were constructed.After that,they are packaged with a single electrode printed with a screen.The structure of porous membranes with different grades and their effects on the permeability,mechanical properties,electrical properties and piezoresistive properties were researched.Experiments show that the porous structures formed by phase separation of homogeneous solutions with different mass fractions have different morphology.With the increase of mass fraction,the pore diameter,pore volume and porosity gradually decrease,and the surface area gradually increases.The more graded the porous is,the more significant difference between the upper and lower layers of porous membrane is.The highest graded porous 10%16%PU@MXene+CNT flexible sensor showed excellent sensitivity over a wide detection range of 0.7 to 20 k Pa,higher than other graded porous membranes,and it has a high stability over 8000 cycles.Its air and moisture permeability are 0.9922 L/m²/s and 1123.6 gm^-2 D^-1,which are 1.35 and 4.40times of those of non-porous membrane respectively.In conclusion,the structure of the highest graded porous 10%16%PU@MXene+CNT flexible piezoresistive sensor is born with high sensitivity,wide detection range and good air and moisture permeability at the same time.In addition,the flexible piezoresistive sensor is used to detect human movement and physiological signals,and its practicability is verified.