Abstract

Flexible strain sensors have received increasing attention with the development of wearable electronic devices. However, integrating wide strain detection range, high sensitivity while maintaining relatively wide linear response range for such sensor system still remain a challenge. A fabric based flexible sensor (S-CNT/PDMS-F) was designed and fabricated, and the sensor can simultaneously achieve high sensitivity, wide linear response and strain detection range by combining self-segregated carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composites and elastic medical bandage. It has been observed that this new sensor system can achieve a high sensitivity with a gauge factor of 615, a large linear responsive range of 0–100% strain (R²=0.993) and a wide strain detection range of ∼200%, which is superior to almost all the reported CNT/PDMS flexible strain sensors. Compared to the similar fabric based strain sensor system deploying non self-segregated structure (C-CNT/PDMS-F), our S-CNT/PDMS-F demonstrates higher electrical conductivity and lower electrical percolation threshold and response time of 55 ​ms, as well as more stable and repeatable performance under cyclic loading conditions. The capability of the sensors in monitoring physiological activities and weight distribution has also been demonstrated.

Background Introduction:

With the rapid development of flexible electronic devices, the demand for high performance conductive polymer composites (CPCs) has steadily increased in many fields, such as medical equipment, human-machine interactions, and soft robotics. In recent years, CPCs consisting of conductive nanofillers embedded within an insulating elastic polymer matrix have been widely used in wearable electronic devices such as flexible strain sensors due to their simple and low-cost preparation processes, controllable electrical conductivity, and excellent mechanical and electrical properties. To date, flexible strain sensors are considered the core technology for wearable electronic devices and have received increasing attention from both academia and industry. Flexible strain sensors with a wide strain detection range, high sensitivity, excellent stability, repeatability and durability are of particular interest to meet the imperative demands of various high-end applications, such as human motion monitoring, electronic skins, and “smart” prosthetics.

Here, a self-segregated CNT/PDMS nanocomposite with a good phase compatibility has been prepared and applied as a coating on elastic medical bandage to obtain a self-segregated CNT/PDMS fabric-based strain sensor. The resulting sensor system has a wide strain detection range, high sensitivity, linearity in response, and high repeatability. The strain sensor has been demonstrated for a range of wearable sensing devices including human motion detection, loading condition monitoring, and recognizing object weight distribution. These promising results demonstrate the strong potential of our low cost sensor system for wide ranging applications such as motion detection, health monitoring, human-machine interactions and intelligent robotics, etc.

Article Highlights:

1. A CNT/PDMS nanocomposite coating with a self-segregated structure was prepared, and the nanocomposite coating was applied to an elastic medical bandage to obtain a fabric-based strain sensor. Due to the presence of self-segregated structure (PDMS particles), the percolation threshold of the strain sensor was reduced (as low as 0.51 wt% CNT), and a 3D conductive network structure was obtained.

2. The fabric-based strain sensor achieved a high sensitivity (GF=615), wide linear response (linearity of R²=0.993 within the strain range of 0-100%), wide strain detection range (up to 200%), fast response time (55 ms), recognition ability for different strains (frequencies), and excellent cyclic stability.

3. The sensor realized the functions of wearable devices, including human motion monitoring, load status monitoring, and recognition of object weight distribution.

Summary and Outlook:

By deploying self-segregated CNT/PDMS nanocomposite as a coating on highly elastic fabric based bandage, a new strategy is proposed for developing low cost, high performance S-CNT/PDMS-F strain sensor with ultrahigh sensitivity and wide strain detection range. The high sensitivity of the sensor (GF = 615) can be attributed to the presence of the self-segregated cross-linked PDMS particles within the nanocomposite coating. Apart from the large total strain detection range (up to 200%), the sensor also demonstrated a promising linear response within strain range 0–100% (R² = 0.993). In addition, compared with strain sensor without self-segregated PDMS, the developed S-CNT/PDMS-F has a faster response time, better signal output response under different frequencies and strains, and its signal stability, repeatability, and durability are improved. The excellent properties of the S-CNT/PDMS-F are also demonstrated for a wide ranging applications such as human movement monitoring, pressure monitoring and the load distribution recognition, etc.

Article Details:

Highly stretchable, sensitive and wide linear responsive fabric-based strain sensors with a self-segregated carbon nanotube (CNT)/Polydimethylsiloxane (PDMS) coating

Libing Liu, Xuezhong Zhang, Dong Xiang, Yuanpeng Wu, Dan Sun, Jiabin Shen, Menghan Wang, Chunxia Zhao, Hui Li, Zhenyu Li, Ping Wang, YuntaoLi

Article Link: https://doi.org/10.1016/j.pnsc.2021.10.012

Author introduction

Dr. Dong Xiang, an associate professor at the School of New Energy and Materials at Southwest Petroleum University, obtained his PhD degree from Queen's University Belfast in the UK. He mainly engages in research on polymer-based composites, additive manufacturing, service behavior and performance optimization of composites for oil and gas field, flexible strain sensors. He is currently a candidate for academic and technological leaders in Sichuan province, a high-level overseas talent in Sichuan province, a member of the Advanced Materials Committee of the Sichuan Science and Technology Collaborative Innovation Promotion Association, and a reviewer for over 30 SCI journals. He is the principal investigator of over 10 projects, including the National Natural Science Foundation of China and International Cooperation Project of Sichuan Province. He has published over 100 SCI papers (H-index 24), authorized over 40 patents, published 2 monographs. He was selected for the "2022 Top 2% Global Scientists List", won the Alan Glanvill Award from Institute of Materials, Minerals and Mining (IOM3) and the Young Scientist Medal from International Association of Advanced Materials (IAAM) in 2022.

Libing Liu, a PhD candidate at the School of New Energy and Materials, Southwest Petroleum University, specializes in the research of flexible strain sensors based on conductive polymer composites, advanced manufacturing technology, fiber surface modification, and the structural and functional integration of fiber reinforced composites. He has published 8 SCI papers, obtained 6 patents, and participated in the writing of one monograph chapter.