Fabrication And Application Of Flexible Piezoresistive Sensors Based On Carbon Nanotubes

E-skin has attracted widespread attention due to its potential applications in wearable health monitoring,smart prosthetics,and robotic skin.The flexible piezoresistive sensor can sense the stimulation of the external environment and convert the pressure into electrical signals or other signal outputs,which is the most important part of the electronic skin.But most flexible sensors do not have the function of moisture permeability,so creating a highly sensitive and moisture permeable flexible sensor remains a key challenge for the development of electronic skin.This subject proposes a simple and effective method to prepare flexible piezoresistive sensor.A non-solvent-induced phase separation method（NIPS）was used to prepare a porous polyurethane film using distilled water as a non-solvent.Carbon nanotubes,which are conductive materials,are attached to porous polyurethane by means of ultrasound to form a uniform conductive network.Then,a carbon nanotube polyurethane（PU@CNT）porous film and a single-sided electrode were assembled into a flexible piezoresistive sensor.The effects of the film-forming structure of different concentrations of polyurethane（10%,12%,15%,18%）on the moisture permeability and mechanical properties and piezoresistance of polyurethane porous films were studied.Porous polyurethane films with different PU concentrations have different structures,and the porous film will change from large-pore irregular structure to small-pore regular structure as the polyurethane concentration increases.The three-dimensional structure of the porous film established by micro-computer tomography（micro-CT）indicates that the porous structure forms channels in the interior of the film,making the film permeable to moisture and air.The porosity of the four concentrations of the porous film were 64.25%,58.03%,52.4%,and 40.27%.Under the temperature and humidity conditions of 32°C and 50 RH%,the air permeability and moisture permeability of 10%-PU@CNT are as high as 6.433L/m²/s and 2059 g m^-2d^-1,which are 8.68 times and 8.01 times of non-porous polyurethane films respectively.And the experimental results show that the moisture permeability does not affect the piezoresistive response of the sensor.Based on the porous structure of the PU@CNT film,the sensitivity of PU@CNT sensor with a PU concentration of 12%can reach a maximum of 51.53 k Pa^-1 under the pressure of 0.7-3k Pa.With the change of the pore structure of the porous film,the hysteresis error of the 18%-PU@CNT ratio is optimized to 67.8%compared to the 10%-PU@CNT sensor,and has high stability（>8000 cycles）and wide sensing range（0-16k Pa）.In order to verify the practicability of the prepared flexible piezoresistive sensor,the sensor was used to detect human physiological signals,human motion,and spatially resolved pressure.