Research On Printed Capacitive Flexible Pressure Sensor Based On New Functional Composite

In recent years,capacitive flexible pressure sensors have received great attention from academic and industrial circles for different applications such as medical health and artificial intelligence.At present,the low-cost preparation of high sensitivity large area flexible pressure sensors is still a huge challenge.A new type of pressure sensitive functional ink that can be used for preparing the dielectric layer of capacitive flexible pressure sensors is proposed.The ink is prepared by three-phase composite of thermal expansion microcapsules,silver nanowires（AgNWs）and polydimethylsiloxane（PDMS）.Using thermally expandable microcapsules to form a controllable microstructure inside the dielectric layer,and adding AgNWs increases the change rate of the relative permittivity of the composite dielectric under pressure,thereby improving the sensitivity of the pressure sensor.Moreover,the flexible pressure sensor array is prepared by screen printing,which can simplify the preparation process and reduce the manufacturing cost.The research content of the thesis mainly includes the following three aspects:（1）The effect of heating temperature and thermal expansion microcapsule weight fraction on the microstructure,mechanical properties and capacitance response of the porous dielectric layer;（2）The influence of AgNWs on the dielectric properties,mechanical properties and capacitance response of the AgNWs/PDMS composite dielectric layer;（3）The preparation method of the pressure-sensitive functional ink,the effect of the printing conditions on the printing quality of the device and the application research of the printing pressure sensor.The research findings of the thesis found that:（1）As the heating temperature increases from 85 °C to 95 °C,the volume expansion ratio of the thermally expandable microcapsules inside the PDMS reaches the maximum,and the particle size range after thermal expansion is 25-75 μm.With the heating temperature and the weight fraction of thermally expanding microcapsules increasing,the elastic modulus of the porous dielectric layer decreases.The thermal expansion microcapsules/PDMS composite with a mass fraction of 10% is prepared by heating at 95 °C to obtain a porous dielectric layer.The sensitivity of the pressure sensor with porous dielectric layer in four different pressure ranges of 0-0.2 kPa,0.2-1 kPa,1-10 kPa,10-45 kPa is 2.9,2.2,2.9,3.4 times of the pressure sensor without microstructures.（2）With the increase of AgNWs mass fraction,the dielectric constant,dielectric loss and elastic modulus of AgNWs/PDMS composite dielectric gradually increase.When the AgNWs mass fraction is 0.5%,the flexible pressure sensor gets the maximum sensitivity of 0.1707 kPa^-1.（3）AgNWs（0.5 wt%）and thermal expansion microcapsules（10 wt%）were mixed with PDMS to prepare composite pressure sensitive functional ink,and screen printing was used to prepare capacitive flexible pressure sensor.The optimal printing quality of the composite pressure sensitive functional ink was obtained with printing condition for the screen mesh number of 300 mesh,the printing speed of 7.2 m/min,the doctor blade angle of 65 degrees and the ink resting time of 7h.The maximum sensitivity of the full printed pressure sensor is 0.255 kPa^-1,the linear range is 0-1 kPa,the minimum detection limit is 1.3 Pa,and the stability is good.The printed pressure sensor can sense the proximity of an object with the longest distance of 24 cm,which is superior to other capacitive pressure sensors reported,and shows good application potential in the fields of object shape recognition and electronic skins.