Studies On Preparation And Temperature Sensitivity Properties Of Flexible Temperature Sensor

In the past few decades,with the rapid development and significant breakthrough of the Internet of Things,the development and promotion of flexible temperature sensors has proved its importance and potential necessity.Polydimethylsiloxane(PDMS)with excellent thermal expansion was selected as the flexible substrate,flake graphite(FG),carbon black(CB)and carbon nanotubes(CNT)were used as conductive filler respectively.The effects of different conductive filler materials and concentration as well as dispersant concentration on the temperature sensitivity of the composites were investigated.At the same time,the temperature-sensitive properties of PEDOT:PSS with excellent visible light transmittance and chemical stability was also investigated.Then,a full screen-printed Wheatstone bridge temperature sensor with high temperature sensitivity and high linearity was constructed.The main structure of this paper is as follows:(1)Firstly,FG/PDMS,CB/PDMS and CNT/PDMS carbon-based flexible temperature sensors were prepared by two-step screen printing method.Experiments show that both FG/PDMS and CB/PDMS composites exhibit positive resistance temperature characteristics(PTC).The low conductive filled FG/PDMS composite is suitable for temperature threshold alarms and the high conductive fill is suitable for flexible temperature sensitive materials.When the mass ratio of cyclohexane/CB increases,the temperature sensitive range of the CB/PDMS composite is enlarged,and more importantly,the linearity of the temperature coefficient of resistance(TCR)is increased.In contrast,CNT/PDMS composite exhibits negative resistance temperature characteristic(NTC).The 10wt%CNT/PDMS composite has a good TCR value of-0.0021 K^-1 as well as an excellent linearity of 99.36%.It is expected to be applied in the field of high precision flexible temperature sensitive materials;(2)The effects of different FG/CNT mass ratios on FG/CNT/PDMS dual-conducting doping composite'TCR were studied.The resistance temperature characteristic test results indicate that the TCR change trend of the FG/CNT/PDMS composite can be regulated by the mass ratio of FG/CNT.The resistance of the composite material is determined by the combined effect of FG expansion and contraction,CNT scalability and interaction between FG and CNT conductive fillers.Most importantly,when the mass ratio of FG to CNT is close to 4:1,the TCR value of the FG/CNT/PDMS composite is almost maintained at the same level of 0.028 K^-1;(3)The effects of isopropanol filling concentration and different conductive additives on the temperature sensitivity of PEDOT:PSS composites were studied.The results show that isopropanol not only reconciles the tackifier of composites to meet the requirements of screen printing,but also has some important effect on the temperature sensitivity of composite.For the composite with 30wt%isopropanol filled,the TCR value decreases as the thermal cycle test progressed;Conversely,for the composite with 70wt%isopropanol filled,the TCR value increases as the thermal cycle test progressed.However,when the isopropyl alcohol filling concentration is 50wt%,the TCR value is substantially stable.The addition of a conductive additive does significantly increase the electrical conductivity of the composite,but the temperature-sensitive properties of composite are severely challenged.Benefit to the excellent compatibility with temperature sensitive materials,it is expected that such composite with significantly improved conductivity can be applied as flexible electrode materials;(4)A high sensitivity flexible temperature sensor is prepared in the form of a full screen-printed Wheatstone bridge.In order to enhance the sensitivity of the temperature sensor,we present a fully screen-printed flexible Wheatstone bridge used for flexible temperature sensing,a positive temperature coefficient and a negative temperature coefficient material were added together in four arms of the Wheatstone bridge,respectively.FG/CNT/PDMS composite with the FG/CNT mass ratio of 1:1 and a total carbon material filling concentration of 16wt%was used as a positive temperature coefficient of resistance material,and the PEDOT:PSS composite with a 50wt%isopropanol filled was used as a negative resistance temperature coefficient material.Within the temperature range of 30-90°C and 10 m A bias voltage,the Wheatstone bridges of the single PTC material,the single NTC material and the coupled with the positive and the negative temperature coefficient materials exhibit an approximately temperature sensitivity of 0.04 V/°C,0.02 V/°C and 0.06 V/°C,respectively,and linearity is higher than 96%.Three consecutive output voltage-temperature tests show similar temperature sensitivities,indicating that this Wheatstone bridge type flexible temperature sensor has excellent stability and is expected to be further applied and promoted in the industrial field.