Flexible Electrospun Nanofibers for Tactile Sensing and Integrated System Research
Flexible pressure sensors have broad applications in wearable healthcare, interactive interfaces, and humanoid robotics. Piezoelectric sensors are especially promising among the available flexible sensors due to their self-powering capability, high sensitivity, mechanical stability, and simple structure. Organic materials offer flexibility and ease of processing, while inorganic materials exhibit strong piezoelectric properties. Combining both types of materials, organic and inorganic, can enhance the overall performance of the sensors.
Polyvinylidene fluoride (PVDF) provides excellent flexibility and breathability, especially when electrospun, making it suitable for electronic skin and health monitoring applications. However, pure PVDF usually generates low output voltage. This limitation can be improved by incorporating nanofillers such as zinc oxide (ZnO).
ZnO is preferred due to its non-toxic properties and ease of synthesis. Recent studies show that combining ZnO and MXene into PVDF significantly enhances piezoelectric output. MXene, a two-dimensional (2D) material with high carrier mobility, further improves performance. This combination offers a promising path for developing sustainable, high-performance, and biocompatible piezoelectric sensors for next-generation wearable electronics.
In this study, a flexible PVDF/ZnO@MXene (PZM) piezoelectric sensor was developed using electrospinning, hydrothermal growth, and spin-coating. Initially, PVDF nanofiber membranes were produced, followed by the growth of ZnO nanorods under hydrothermal conditions. A 5% MXene solution, obtained by etching MAX phase materials, was then spin-coated to form the PZM active layer. Finally, the sensor was assembled with copper electrodes and encapsulated with a polyurethane film, completing the flexible PZM device.
The synergy between PVDF nanofibers and ZnO substantially enhanced the piezoelectric performance. MXene formed micro-capacitors and a three-dimensional (3D) conductive network, boosting charge storage and transfer. This sensor effectively detected physical contact and subtle physiological signals. Integrating it with Indium tin zinc oxide (ITZO) thin-film transistors (TFTs) further improved signal output and stability.
The PZM sensor demonstrates excellent performance, showing a high sensitivity reaching 2.32 V/N. It also shows a fast response time of 46 ms and a recovery time of 52 ms. The sensor can detect subtle signals like a 30 mV response from light leaf contact and up to 3 V under a 500 g weight. It effectively monitors dynamic events and physiological signals such as throat vibrations, pulse, and electrocardiogram (ECG) waveforms. When integrated with a TFT, the sensor output increases from 200 mV to 1.8 V under a 0.1 N force, enhancing signal clarity. After undergoing 500 cycles under 2 N force, it maintains a stable output of approximately 3.82 V, confirming its high durability.
The PZM sensor demonstrates superior performance by offering higher sensitivity at a lower pressure range, which is attributed to the synergistic integration of functional materials. Furthermore, the integration of TFT leads to nearly 10-fold signal amplification, thus significantly enhancing the ability of the sensors to detect subtle signals. These advantages highlight the competitiveness of the PZM sensors over existing sensors and provide valuable insights for developing smart sensor networks, particularly within the expanding landscape of the Internet of Things (IoT).