High-performance flexible piezoresistive strain sensor based on biaxially stretched conductive polymer composite films with reduced graphene oxide-carbon nanotubes
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摘要: 随着现代科技的快速发展及人们生活水平的提高，柔性压阻传感器在人体健康监测、智能机器人、可穿戴电子设备和人机交互等方面展现了巨大应用潜力。本文采用Hummer’s法制备了还原氧化石墨烯(rGO)，其后通过静电组装将碳纳米管(CNT)负载在rGO的表面上，并将其引入热塑性聚氨酯(TPU)基体中制备成导电纳米复合材料。此外，采用逐次双向拉伸技术实现了基体中纳米填料的进一步分散和平行取向，并基于所获得的复合薄膜研制出了一种可监测微小应变的高性能柔性压阻传感器。研究发现，rGO-CNT/TPU4×4传感器(拉伸比为4×4)在保持高灵敏度(1.5%应变的情况下灵敏度(GF)=46.7)和高线性度(R2=0.98)的同时，能够适用于不同应变和频率变化，并且在循环加载测试中展出优异的稳定性和可重复性。该柔性压阻传感器可以用于识别细微的人体生理活动，包括脉搏和呼气等。此外，还设计制备了一个可压缩的传感器阵列来监测在不同压力下的信号变化情况。本研究对于高性能柔性压阻应变传感器的快速宏量制备及结构与性能调控具有重要的科学指导意义。Abstract: In recent years, flexible piezoresistive sensors have shown great application potential in human health monitoring, smart robots, wearable electronic devices, and human-computer interaction, while it is challenging to efficiently fabricate highly sensitive and low-cost flexible piezoresistive sensor for detecting micro strains. In this work, reduced graphene oxide (rGO) was prepared by Hummer's method, then carbon nanotubes (CNTs) were immobilized on the surface of rGO by electrostatic assembly. Subsequently, the hybrid nanofillers were introduced into thermoplastic polyurethane (TPU) matrix to prepare conductive polymer composite. The further dispersion and parallel orientation of nanofillers in the matrix were achieved by the sequential biaxial stretching process. It is shown that the sensor prepared by biaxially stretched conductive polymer composite exhibits higher sensing performance compared to the sensor without experiencing biaxial stretching. The rGO-CNT/TPU4×4 sensor (with a stretching ratio of 4×4) shows high sensitivity (GF=46.7 at 1.5% strain), high linearity (R2=0.98), responsive capability to different strains and frequencies, excellent stability and repeatability in cyclic loading tests. The flexible piezoresistive sensor can be used to identify subtle human physiological activities, including pulse and exhalation. In addition, a compressible sensor array was fabricated to achieve accurate identification of weight distribution. This study provides an important scientific guidance for the rapid large-scale fabrication and structure and property tuning of high-performance flexible piezoresistive strain sensors.
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Key words:
- biaxial stretching /
- strain sensor /
- self-assembly /
- reduced graphene oxide /
- carbon nanotube
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图 1 逐次双轴拉伸的示意图
Figure 1. Schematic description of the sequential biaxial stretching process
MD—Machine direction; TD—Transverse direction
图 2 石墨 (a) 、氧化石墨烯(GO) (b)、还原氧化石墨烯(rGO) (c) 和rGO-碳纳米管(CNT) (d) 的SEM图像；rGO (e) 和rGO-CNT (f) 的高分辨率TEM图像
Figure 2. SEM images of graphite (a), graphene oxide (GO) (b), reduced graphene oxide (rGO) (c) and rGO-carbon nanotube (CNT) (d); High resolution TEM images of rGO (e) and rGO-CNT (f)
图 3 rGO/TPU1×1 (a)、rGO/TPU4×4 (b)、rGO-CNT/TPU1×1 (c) 和rGO-CNT/TPU4×4 (d) 的SEM图像
Figure 3. SEM images of rGO/TPU1×1 (a), rGO/TPU4×4 (b), rGO-CNT/TPU1×1 (c) and rGO-CNT/TPU4×4 (d)
图 4 不同拉伸比下rGO/TPU和rGO-CNT/TPU电导率的变化 (a)、rGO/TPU4×4和rGO-CNT/TPU4×4复合材料电阻随温度的变化 (b)
Figure 4. Change of conductivity of rGO/TPU and rGO-CNT/TPU under different stretching ratios (a),and resistance of rGO/TPU4×4 and rGO-CNT/TPU4×4 composites varied with temperature (b)
图 5 压阻传感器的灵敏度(GF) (a) 和传感器在不同压力下的相对电阻变化ΔR/R0 (b)
Figure 5. Gauge factor (GF) as a function of piezoresistive strain (a) and relative resistance variation ΔR/R0 of the sensor under different forces (b)
图 6 应变传感器在0.5%应变和不同频率下的相对电阻变化((a), (b))；应变传感器在0.1 Hz频率和不同应变下的相对电阻变化((c), (d))
Figure 6. Relative resistance change of strain sensors during a cyclic loading at a strain of 0.5% and different frequency ((a), (b)); Relative resistance of the strain sensors with different nanofillers under cyclic loading at different strain and frequency of 0.1 Hz ((c), (d))
f—Frequency; ε—Strain
图 7 应变传感器在应变为0.5%和频率为0.1 Hz的500个周期中的稳定性：(a) rGO/TPU4×4；(b) rGO-CNT/TPU4×4
Figure 7. Stability of strain sensors during 500 cycles at a strain of 0.5% and a frequency of 0.1 Hz: (a) rGO/TPU4×4; (b) rGO-CNT/TPU4×4
图 8 传感器对加载/卸载垫片 (a)、硬币 (b)、呼气 (c) 和脉冲 (d) 的信号响应
Figure 8. Electromechanical responses of the sensor to loading/unloading gasket (a), coins (b), exhalation (c) and pulse (d)
图 9 rGO-CNT/TPU4×4传感器阵列的应用((a)传感器阵列的示意图；(b)一个3×3的传感器阵列上放置棋子；(c)棋子的质量分布；(d)相应的信号响应)
Figure 9. Application of rGO-CNT/TPU4×4 for a sensor array ((a) Schematic of the sensor array; (b) A 3×3 sensor array loaded by chess pieces; (c) Mass distribution of chess pieces; (d) Corresponding signal responses)
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