Conductive polymer composites (CPCs) can be developed into flexible sensing systems because of their excellent flexibility and sensitivity to external stimulation. A recent study available as a pre-proof in the journal Carbon focuses on creating a multifunctional sensor based on CPCs consisting of thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs).
Study: Highly-stretchable porous thermoplastic polyurethane/carbon nanotubes composites as a multimodal sensor. Image Credit: nevodka/Shutterstock.com
What are Stretchable Sensors?
Due to the pressing demand for electronic interfaces, adaptable screens, smartwatches, and flexible robotic systems, the production of stretchable sensors that can be used to detect external stimuli is expanding rapidly. Stretchability is critical because it makes devices comfortable and more effective when used in human health and motion detection applications. Several approaches for fabricating stretchable sensing devices with detailed structural design and material refinement have emerged in recent years.
Utilizing Conductive Polymer Composites (CPCs)
Conductive polymer composites (CPCs) comprised of elastic polymers and conductive materials are among the finest candidates for constructing stretchable detectors owing to their excellent machinability, wear resistance, cost-effectiveness, high flexibility, and adaptability. CPCs are highly stretchable due to their elastic polymer, while conductive elements act as detecting components in reaction to environmental stimuli, including strain, pressure, temperature, and moisture.
Limitations of Traditional CPC-based Stretchable Sensors
Conventional CPC-based flexible sensors are made by mechanically injecting conducting materials, particularly carbon-containing nanoparticles, into a flexible and elastic matrix material to create a three-dimensional (3D) linked composite material. When the sensors are subjected to external stimuli, the inner conducting networks change as the polymer matrix deforms, causing variation in electronic signals.
However, to build a flawless 3D conducting system, carbon-containing nanoparticle-filled CPCs often need a significant number of conducting nanoparticles, leading to an increase in workability and a reduction in CPC mobility. Furthermore, owing to poor compatibility, it is challenging to scatter inorganic conductive nanoparticles evenly in a polymeric matrix. This, in turn, compromises the sensor performance and operational use of the sensing devices.
Development of a Novel Multimodal Stretchable Sensor
To address the limitations of standard CPC-based sensors, a technique for evenly dispersing conductive elements throughout the polymer matrix must be outlined. Filtering, impregnation, or ultrasonography may be used to load conductive elements onto a stretchy 3D polymer skeleton.
In this study, the researchers created a highly flexible multifunctional sensor using thermoplastic polyurethane (TPU) permeable framework with carbon nanotubes (CNTs). The newly created multimodal sensor has excellent repeatability and accuracy when it comes to strain, pressure, and temperature measurements.
Fabrication and Characterization of TPU and CNT-Based Composites
The researchers used vapor-induced separation (VIPS) and ultrasound-assisted anchoring methods to produce novel TPU and carbon nanotube-based porous composites.
VIPS prepared the permeable TPU framework first. Moisture from the surrounding environment was collected on the surface of the TPU mixture, resulting in phase separation and the creation of a porous microstructure in the TPU skeleton. The permeable TPU skeleton was then anchored with carbon nanotubes using an ultrasound-assisted immersion in a carbon nanotube/water solution.
Scanning electron microscopy was used to characterize the surface topologies of TPU@CNT materials with a multilayer porous structure. The electrical and mechanical properties were determined using a digit precision multimeter in conjunction with universal tensile testing equipment. A hot stage connected with a digit precision multimeter was used to evaluate the thermal sensing capabilities of TPU@CNT materials.
Key Findings of the Research
The novel CPC-based multimodal sensor has an extraordinarily low strain threshold of 0.01 percent and an extremely broad strain detection range of 0.01-900 percent, which is superior to most earlier described CPC-based strain sensors. With a large enough strain, the detector can sense minute physiological signals and movement patterns.
The sensor also exhibits a reproducible and consistent electric signal to pressure stimulation, due to the bidirectional development of the CNT network and the stretchability of the 3D permeable TPU framework. As a result, the sensor produced in this manner is capable of sensing the tactile impulses associated with stretching and compressing. Additionally, the sensor has an excellent temperature detecting capability due to the linear NTC effect.
Importance for Future Applications
The present work used VIPS and ultrasound-assisted anchoring methods to produce a highly stretchable porous TPU@CNT composite for use as a multifunctional sensor. The novel multimodal sensor has tremendous promise in the realms of electronics, wearable technology, and human-computer interaction due to its extreme flexibility and exceptional multimodal functionalities. Additionally, it can be employed to develop advanced human wellbeing and motion detection systems.
Reference
Zhu, G. et al. (2022). Highly-stretchable porous thermoplastic polyurethane/carbon nanotubes composites as a multimodal sensor. Carbon. Available at: https://www.sciencedirect.com/science/article/pii/S0008622322003116?via%3Dihub
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