Electrospinning Device for Nanofibers| Source Dependence of Polyacrylonitrile ElectrospunNanofibers on Piezoelectric Responset
Views: 1646
Author: Nanofiberlabs
Publish Time: 2025-06-18
Origin: Polyacrylonitrile (PAN)
Team of Wang Hongxia/Lin Tong from Tiangong University & Team of Chang Haibo from Henan University in 《JMCA》: Analysis on the Mechanism of Raw Material Dependence of Piezoelectric Response of Electrospun Polyacrylonitrile Nanofibers.
Polyacrylonitrile (PAN) nanofibers, due to their high flexibility, easy processability, and significant piezoelectric effect, are regarded as a new generation of intelligent materials to replace traditional polyvinylidene fluoride (PVDF), and have great potential in the fields of flexible sensing, self-powered electronics, etc. However, the piezoelectric properties of PAN nanofibers reported in different literatures can vary by orders of magnitude, which seriously restricts the process of their standardized application. The root cause is that the regulation mechanism of raw material sources on the intrinsic piezoelectric properties of materials has not been clarified, which has become a key scientific problem pending solution in the field for a long time.
Aiming at this challenge, the team of Professor Wang Hongxia and Professor Lin Tong from Tiangong University, in collaboration with the team of Professor Chang Haibo from Henan University, published a research paper entitled "Source-Dependent Piezoelectricity of Electrospun Polyacrylonitrile Nanofibers: From Molecular Conformation to Energy Harvesting Performance" in 《Journal of Materials Chemistry A》. This work first establishes a full-chain structure-property relationship of PAN raw material source-molecular conformation-solid state structure-piezoelectric performance, providing a new strategy for the rational design of high-performance piezoelectric materials.
The research team selected PAN raw materials from five international suppliers such as Sigma-Aldrich and J&K Scientific, and prepared nanofiber membranes with uniform morphology (fiber diameter ≈ 330 nm, thickness ≈ 60 μm) under strictly controlled parameter conditions, and systematically explored the synergistic effects of parameters such as molecular weight distribution, molecular structure, molecular conformation in the solid state, impurity content, piezoelectric output, dielectric properties, water absorption, surface charge, and tensile strength.
The study found that under the same force conditions, the open circuit voltage of piezoelectric devices made of nanofiber membranes prepared from different sources of PAN differed by up to 4.6 times, and the output power differed by 15 times. Among them, the nanofiber membrane prepared from PAN of Sigma-Aldrich had the best piezoelectric performance, with the peak-to-valley value (Voc-pp) of Voc reaching 84.3 V, while the output performance of the nanofiber membrane prepared from PAN of Macklin was the lowest, with Voc-pp only 18.5 V. They showed similar trends in the piezoelectric coefficient d33. After removing the surface static charge of the film by the conventional alcohol solution method, it not only did not affect the piezoelectric output, but even caused an increase in Voc-pp.
Figure 1: a) Schematic diagram of the electrospinning equipment; b) The morphology of the typical electrospun PAN nanofibers (scale: 1 μm), c) Diameter distribution histogram; d) Piezoelectric device structure, e) Schematic diagram of energy conversion test; f-h) Piezoelectric output and i) Power-load (P~R) curve.
There are subtle differences in molecular structure and composition among PAN nanofibers from different sources. PAN-SA and PAN-JK are homopolymers with relatively single molecular chain structures; PAN-AL, PAN-MA, and PAN-SP are copolymers containing a small amount of comonomers such as acrylamide, methyl methacrylate, or acrylic acid, leading to changes in the polarity and regularity of the molecular chains. All PAN raw materials contain trace ionic impurities (such as NH₄⁺), but their contents and distributions vary depending on the suppliers.
PAN nanofiber membranes from different sources showed significantly different hydrophilic/hydrophobic properties. Among them, PAN-AL had the smallest water contact angle and the fastest water diffusion speed, indicating the strongest surface polarity. Although there were large differences in the molecular weight and molecular weight distribution of PAN raw materials from different sources, these differences did not have a significant impact on the electrospinning process and fiber morphology. The mechanical properties (such as tensile strength, modulus) of PAN nanofiber membranes from different sources varied significantly, which may be related to the arrangement of molecular chains and internal defects of the fibers. However, their dielectric constants and dielectric losses differed little, indicating that the polarization ability mainly depends on the dipole orientation of the molecular chains rather than the macroscopic mechanical properties.
Figure 2: a) The dynamic change of the initial contact angle with time of the PAN nanofiber membrane, b) Water content, c) Voc-pp before and after removing the residual charge, d) Dielectric constant and dielectric loss, e) Stress-strain curve, f) Young's modulus, g) Tensile strength and h) Elongation at break.
The research team found that the differences in piezoelectric performance mainly depend on three key factors:
Molecular conformation: The content of planar zigzag conformation (Φ) is still the main determinant of piezoelectric activity. PAN-SA with the highest content of planar zigzag conformation (Φ=66.1%) showed the highest piezoelectric performance.
Comonomer units: The content of comonomer units exceeding >2% will lead to the decrease of piezoelectric performance, which may be related to the expansion of molecular spacing induced by copolymers, causing lattice distortion and inhibiting the formation of zigzag conformation.
Ionic impurities: Ionic impurities may promote the formation of planar zigzag conformation, thereby increasing the piezoelectric performance of PAN.
The research team further verified the differences in application performance of PAN nanofiber membranes from different sources. When used to light up commercial LEDs, these devices (the area of PAN nanofiber membranes is all 5 cm²) can light up different numbers of LEDs. The PAN-SA device can light up 10 commercial LEDs, and the performance is far better than other raw materials. When charging the capacitor, the PAN-SA device can charge a 4.7 μF capacitor to 3.0 V within 3 minutes, and the charging rate is 1.2-2 times that of other materials, highlighting the advantages of engineering applications.
Figure 3: a) The circuit diagram of the electric energy generated by the PAN nanofiber piezoelectric device driving commercial LEDs or charging the capacitor, b) The photo of the maximum number of LEDs lit by different PAN nanofiber devices, c) The voltage-time change curve during the charging process of the 4.7 μF capacitor.
This study breaks through the traditional "process-dominated" optimization paradigm of piezoelectric materials, and for the first time reveals the cascade regulation mechanism of the intrinsic properties of raw materials on the polarization efficiency of PAN nanofibers, providing a theoretical cornerstone for establishing a raw material-performance database and formulating industry standards. It will accelerate the development of a new generation of PAN-based piezoelectric materials with high stability and low batch sensitivity, and promote the standardization and industrialization of flexible electronics and energy harvesting technologies.
