Wearable color-changeable strain sensor based on polyacrylamide organogel
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摘要: 柔性应变传感器在可穿戴医疗设备、电子皮肤等领域具有广泛的应用前景，然而传统柔性应变传感器只能输出电信号，缺乏对应力应变的直接可视化响应，限制了其在应力预警、健康监测等方面的应用。本文以柔性透明银纳米线(Silver nanowire，AgNW)/硅橡胶薄膜为电极，以浸渍有机电致变色染料和锂离子的聚丙烯酰胺有机凝胶(Polyacrylamide，PAAm)为变色单元，成功制备了一种具有三明治结构的柔性可变色应变传感器。研究结果表明，该PAAm传感器具有优异的拉伸和压缩回弹性及中等应变响应性能(响应灵敏度为0.7)，此外它可在外力作用下产生颜色变化，实现对应变的可视化响应。该传感器在交互式可穿戴设备、电子皮肤、防伪、人工假肢和智能机器人等方面具有广阔的应用前景。Abstract: Flexible strain sensor has great potential in medical industry, health care and robotics, etc. However, most flexible strain sensors reported only output electrical signal (e.g. resistance, current and capacitance) in response to external strain, and lack direct notice of external loading, restricting their applications in early warning and health care, etc. In this work, we produced a flexible color-changeable strain sensor by using the silver nanowire (AgNW)/silicone composite film as the transparent electrode and polyacrylamide organogel as the electrochromic component. In addition to the excellent flexibility and moderate strain sensing performance (strain sensitivity of 0.07), the senor obtained has a reversible color transformation in response to external strain via the electrochromic effect. In virtue of these advantages mentioned above, the current sensor has broad applications in interactive wearable devices, electronic skin, anti-counterfeiting, artificial prosthetics and intelligent robots.
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Key words:
- flexibility /
- transparent electrode /
- electrochromic /
- visualization /
- strain sensor
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图 2 银纳米线(AgNW)/聚二甲基硅氧烷(PDMS)透明导电薄膜的制备流程图
Figure 2. Synthesis of the transparent and conductive silver nanowires (AgNW)/polydimethylsiloxane (PDMS) film
图 3 (a) AgNW的SEM图像；(b)~(f) AgNW/PDMS薄膜的SEM图像；(g) AgNW/PDMS薄膜的表面电阻率；(h) AgNW/PDMS薄膜的光学照片；(i) 氧化铟锡(ITO)和AgNW/PDMS薄膜在可见光区的透光率
Figure 3. (a) SEM image of AgNW; (b)-(f) SEM images of AgNW/PDMS films; (g) Surface resistivity of AgNW/PDMS films; (h) Optical image of AgNW/PDMS films; (i) Optical transmission of Indium tin oxide (ITO) and AgNW/PDMS films
图 4 (a) 纯PDMS和AgNW-1.5/PDMS薄膜的典型拉伸应力-应变曲线；(b) AgNW-1.5/PDMS薄膜在1000次拉伸循环载荷作用下的力学响应
Figure 4. (a) Typical tensile stress-strain curves of the pure PMDS and AgNW-1.5/PDMS film; (b) Mechanical behavior of AgNW-1.5/PDMS film under 1000 cycles of tensile loading
图 5 (a) 聚丙烯酰胺(PAAm)气凝胶的光学照片；(b) PAAm气凝胶的SEM图像；(c) PAAm有机凝胶的光学照片；(d) MBI和PAAm气凝胶的FTIR图谱；(e) PAAm有机凝胶的典型拉伸应力-应变曲线
Figure 5. (a) Optical image of polyacrylamide (PAAm) aerogel; (b) SEM image of PAAm aerogel; (c) Optical image of PAAm orangogel; (d) FTIR spectrum of MBI and PAAm aerogel; (e) Typical tensile stress-strain curve of PAAm organogel
图 6 PAAm传感器的力学特性：(a) 典型拉伸应力-应变曲线；(b) 加载频率为0.1 Hz、1 Hz和10 Hz，加载应变为10%时的循环拉伸应力曲线；(c) 1000次循环拉伸载荷下的应力变化曲线；(d) 典型的压缩应力-应变曲线；(e) 加载频率为0.1 Hz、1 Hz和10 Hz，加载应变为50%时的循环压缩应力曲线；(f) 1000次循环压缩载荷下的应力变化曲线
Figure 6. Mechanical behavior of PAAm sensor: (a) Typical tensile stress-strain curve; (b) Stress under cyclic tensile strain of 10% at the frequency of 0.1, 1 and 10 Hz; (c) Stress under 1000 cycles of tensile loading; (d) Typical compressive stress-strain curve; (e) Stress under cyclic compression strain of 50% at the frequency of 0.1, 1 and 10 Hz; (f) Stress under 1000 cycles of compressive loading
图 7 (a) PAAm传感器的相对电阻变化(RCR)-压缩应变曲线；(b) PAAm传感器对不同频率30%压缩应变的RCR响应曲线；(c) PAAm传感器随电压变化的光学照片；(d) PAAm传感器的循环伏安曲线
Figure 7. (a) Change in relative resistance (RCR)-compression curve of the PAAm sensor; (b) RCR curves of the PAAm sensor response to compressive strain of 30% at 0.1, 1 and 10 Hz; (c) Optical images of the PAAm sensor at varied voltage; (d) Cyclic voltammogram curves of the PAAm sensor
图 8 ((a)、(b)) PAAm传感器用于手腕运动和膝盖运动监测；(c) 传感器用于应变可视化的电路图；(d) 按压模式下传感器的颜色变化；(e) 手指按压后传感器应变分布的有限元模拟
Figure 8. ((a), (b)) PAAm sensor to wrist movement and knee movement; (c) Circuit diagram of the PAAm sensor for direct visualization of strain; (d) Color change of the sensor under pressure; (e) Finite element simulation of the strain distribution of the PAAm sensor pressed by a thumb
R0—Initial resistance; RL—Resistance load
表 1 AgNW/PDMS复合薄膜的命名
Table 1. Naming of AgNW/PDMS films
Sample Concentration of AgNW/(mg·mL−1) AgNW-1/PDMS 0.01 AgNW-1.5/PDMS 0.015 AgNW-2/PDMS 0.02 AgNW-2.5/PDMS 0.025 AgNW-3/PDMS 0.03 
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