Study On Fabrication And Performances Of Flexible Strain Sensor Based On Low Dimensional Nanomaterials And Microstructured Substrates

Recently flexible electronic devices,especially flexible strain sensors,have attracted extensive attention for their potential applications in various areas such as wearable devices,electronic skin,human-machine interface,intelligent robots,flexible display,and smart healthcare due to these advantages of wearability,high performance,low cost,portability,and biocompatibility.However,flexible strain sensors based on single nanomaterials and polymer substrates are still facing some urgent problems.It is difficult to achieve the high sensitivity and large stretchability in flexible strain sensors simultaneously with better comprehensive performances.Recent researches have showed that multi-components nanomaterials and microstructured substrates could improve their functions as flexible strain sensors effectively.One hand,atomic layer deposition(ALD),because of unique self-limiting and self-saturation reaction mechanism,enables the deposited nanomaterials with large area uniformity,simple and precise thickness control,and excellent three-dimensional conformality.On the other hand,biomimetic method is a cheap,convenient and environment-friendly route to fabricate microstructured substrates.To solve the above-mentioned problems,in this thesis,several kinds of flexible strain sensors have been prepared and attempted.Among them,sensors based on Ir nanoparticle decorated multi-wall carbon nanotubes(Ir NPs@MWCNTs)and duck web/rose petal patterned polydimethylsiloxane(PDMS)films were obtained by combination of ALD and biomimetic methods,and sensors based on MWCNTs-Ag nanowires(Ag NWs)and elastic cords with cotton textile fibers were fabricated by ultrasonic mixing method.The influences of ALD cycles for Ir NPs,substrate patterns and various nanomaterials ratios on the performances of the sensors has been investigated carefully,as well as their practical applications in human motion monitoring and phonation detection.Main achievements are summarized as follows1.The effect of ALD Ir cycles of 100,200 and 300 on the performances of strain sensors of Ir NPs@MWCNTs and duck web patterned PDMS has been investigated.The biomimetic flexible strain sensors of Ir NPs@MWCNTs on duck web patterned PDMS show superior sensitivity(34.96),larger sensing range(0-30%),better stability(>10000 stretch and release cycles),and fairly faster response time(150 ms)under optimal 200 ALD Ir cycles due to the uniform distribution of Ir NPs on MWCNTs.It is attributed to the synergic effect of utilizing patterned PDMS films copied from duck webs as substrates and Ir NPs@MWCNTs as sensing materials.Its maximum gauge factor is about 3.6 times higher than the sensor based on MWCNTs and duck web patterned PDMS film and 21.3 times higher than the sensor based on MWCNTs and flat PDMS film.After more than 10000 strain cycles,the sensor current drifts about 10.8%from 2.83×10-8 A to 3.14×10-8 A,which demonstrates the long-term stability of the sensor.2.Similarly,the flexible strain sensor based on 200 ALD cycles Ir NPs@MWCNTs and petal patterned PDMS film exhibits optimal performances.Its maximum gauge factor is about 20.33,which is about 7.2 times more than the sensor based on MWCNTs and petal patterned PDMS film,and is about 24.1 times more than the sensor based on MWCNTs and flat PDMS film Its stretchablilty attains 35%strain,3.7 times higher than the sensor based on MWCNTs and flat PDMS film.The response and recovery time is 200 and 250 ms,respectively.After 9000 strain cycles,the sensor current drifts about 9.9%from 5.27×10-6 A to 5.79×10-6 A,showing a rather good long-term stability.Above all,biomimetic flexible strain sensors based on 200 ALD cycles Ir NPs@MWCNTs and duck web/rose petal patterned PDMS films show improved comprehensive performances,which is attributed to the synergic effect of low dimensional Ir NPs@MWCNTs as sensing materials and biomimetic microstructured PDMS films as substrates.3.The impact of MWCNTs-Ag NWs mass ratios of 1:5,1:15,1:20,1:30,1:50 and 1:100 on the performances of strain sensors of MWCNTs-Ag NWs and elastic cords has been examined.The flexible strain sensor based on 1:30 MWCNTs-Ag NWs and elastic cords shows best sensing functions.Its maximum gauge factor is about 415.99,which is 17.3 times higher than sensor based on MWCNTs and elastic cord,and 21.3 times higher than sensor based on Ag NWs and elastic cord.It exhibits maximum stretchability of 70%with faster response and recovery time of 195 and 189 ms,respectively.After 9000 strain cycles,the sensor current only changes from 2.71 ×10-7 A to 2.78×10-7 A with drift value of?2.6%,indicating the excellent long-term stability.The better comprehensive performances such as superior sensitivity,larger stretchable range and long-term stability can be ascribed to the MWCNTs/Ag NWs synergistic conductive network with 1:30 ratio as well as the microstructurd elastic cords with cotton textile fibers.4.Several flexible strain sensors have been applied in human movement detection such as the motion of finger,wrist,palm,and swallow,pulse monitoring,and phonation detection.The experimental results indicate faster response,accurate detection,and better repeatability.Overall,flexible strain sensors based on Ir NPs@MWCNTs and duck web/rose petal patterned PDMS films,and MWCNTs-Ag NWs and elastic cords might have promising applications in wearable electronics,electronic skin,intelligent robots,smart healthcare,and so on.