Preparation Of Surface Micro-Structured TPU/CNTs Porous Materials And Research On Piezoresistive Properties

As flexible pressure sensors are widely used in the fields of healthcare,electronic skin and human-computer interaction,the requirements for their performance are also increasing.However,conventional flexible pressure sensors suffer from low sensitivity,so researchers have proposed the introduction of surface microstructures and porous structures to improve the sensitivity of sensors,and this has become a hot area of current research.In this study,thermoplastic polyurethane（TPU）was used as the polymer matrix and carbon nanotubes（CNTs）as the conductive filler,and a simple template method combined with supercritical carbon dioxide（Sc-CO₂）foaming process was used to prepare surface microstructure TPU/CNTs porous pressure sensors.The results showed that the synergistic effect of surface microsphere structure and porous structure significantly improved the sensitivity of the sensor.The main studies are as follows:（1）TPU/CNTs pressure sensors with surface microsphere structure were prepared by the solution method combined with glass templates,and the effect law of different CNTs content on the conductivity and piezoresistive sensitivity was systematically investigated.The results showed that the percolation threshold of TPU/CNTs nanocomposites was 2 wt.%.The introduction of microsphere structure effectively improved the piezoresistive sensitivity,in which the MTPUC₅ pressure sensor exhibited the highest piezoresistive sensitivity(0.151 kPa^-1,0～2 kPa).The sensor offers excellent piezoresistive performance,including fast response（response time≤250 ms）and a wide operating range（0～80 kPa）for monitoring a wide range of human physiological signals.In addition,the mechanism of introducing a microsphere structure to improve the piezoresistive sensitivity was elucidated by Abaqus finite element software.（2）In order to improve the piezoresistive sensitivity,the Sc-CO₂ foaming process and introduces the cell structure inside the MTPUC₅ pressure sensor to study the effect of different bubble structures on the piezoresistive sensitivity.The results show that with the increase of foaming temperature,the diameter of vesicles increases,the density of vesicles decreases,and the piezoresistive shows a trend of first increasing and then decreasing;while with the increase of foaming pressure,the diameter of cell decreases,the density of cell increases,and the piezoresistive shows a trend of increasing.Among them,the micro spherical FTPUC₅T₁₀₀P₂₀ pressure sensor shows the best piezoresistive sensitivity(0.285 kPa^-1,0～2 kPa).The sensor offers excellent piezoresistive performance:fast response time（response time≤100 ms）,wide operating range（0～80kPa）,and stability over 1000 cycles.In addition,it can be used to monitor a wide range of human physiological signals（facial activity,small arm muscle contractions and arterial pulses,etc.）（3）To further improve the piezoresistive sensitivity,TPU/CNTs porous pressure sensors with different microstructures on the surface（square-shaped,single-ridged and double-ridged）are prepared in this chapter based on the research basis of section（1）and（2）.The effect of different surface microstructures on the piezoresistive sensitivity was systematically investigated.The results showed that the double-ridge FTPUC₅T₁₀₀P₂₀sensor exhibited the best piezoresistive sensitivity(0.309 kPa^-1,0～2kPa)and showed fast response capability（response time≤80 ms）and super 600 cycles stability.In addition,the sensor has excellent ability to detect small tension motions such as dorsal skin folds,cervical muscle contractions,small arm muscle contractions and arterial pulses,and can provide timely signal feedback to external temperature changes.