Electrospinning Equipment: Electrospun and Dip-Coated PI/PTFE@PI Nanocomposite Dielectric Membranes

In the era of rapid development of modern communication technologies, the demand for high - performance dielectric materials is soaring. With the continuous advancement of 5G and the approaching 6G communication technologies, high - frequency communication devices have stringent requirements for materials with outstanding dielectric properties, high heat resistance, and remarkable mechanical strength. Polyimide (PI), renowned for its excellent comprehensive properties, has gained significant attention in the dielectric field. However, its relatively high traditional dielectric constant restricts its application in high - performance integrated circuits. On the other hand, polytetrafluoroethylene (PTFE) possesses excellent dielectric properties and chemical stability. Combining these two materials holds the promise of creating dielectric materials that can meet the needs of high - frequency communication. This article delves into the research on preparing PI/PTFE@PI nanocomposite membranes using an electrospinning device and the dip - coating method, highlighting their vast potential in the dielectric field.  

I. Research Content

(1) In this research, an electrospinning machine was utilized to prepare nanofiber membranes consisting of PI and PTFE. The process was carried out with specific experimental parameters, such as a voltage of 20 kV and a needle - to - collector distance of 25 ± 1 cm. Subsequently, the dip - coating technique was adopted. The nanofiber membranes were immersed in a 10% polyamic acid (PAA) solution and then underwent an imidization treatment, successfully fabricating PI/PTFE@PI nanocomposite membranes (for the preparation process, refer to Figure 1).

(2) Thermal Stability: The composite membranes demonstrate high thermal stability. According to thermogravimetric analysis (TGA) (refer to Figure 2a), the initial decomposition temperature of PI - CM is 450°C, while that of the PI/PTFE@PI composite membrane is 407°C. Nevertheless, all composite membranes maintain high weight stability above 400°C. The maximum thermal degradation temperature (Tmax) of the composite membranes ranges from 641 - 659°C, close to the 659°C of the pure PI composite membrane; the 5% weight loss temperature (Td5%) is between 407 - 450°C. Although the addition of PTFE lowers the initial decomposition temperature of the composite membrane, its overall thermal stability can still satisfy the requirements of practical applications.

(3) Mechanical Properties and Abrasion Resistance: The CM - 20% composite membrane exhibits excellent mechanical properties, with a tensile strength reaching 26.8 MPa (the data is sourced from Figure 2d). From the tensile test results, the tensile stress of the PI/PTFE@PI composite membrane is significantly higher than that of the PI - CM membrane. However, as the PTFE content increases, the tensile strength first rises and then declines. This is because an appropriate amount of PTFE helps form a nanofiber - bonding structure, enhancing the tensile strength. Conversely, excessive PTFE, due to its low tensile strength, reduces the overall strength of the composite membrane. In terms of abrasion resistance, CM - 20% performs optimally (refer to Figure 3). The coated membrane has significantly enhanced abrasion resistance compared to the uncoated one, which is attributed to the interlocking of nanofibers in the composite membrane, providing physical reinforcement.

(4) Dielectric Properties: The dielectric constant of the composite membranes ranges from 1.24 to 2.00, and the dielectric loss ranges from 0.008 to 0.071 within the frequency range of 8.2 - 12.4 GHz. As shown in Figure 4, the dielectric constant of the uncoated pure PI nanofiber membrane is approximately 1.21 at a frequency of 10 GHz. After coating, it increases to 1.64. Among them, the CM - 10% sample has the highest dielectric constant, reaching 1.99. Regarding dielectric loss, the dielectric loss of the uncoated pure PI nanofiber membrane is 0.001 at 10 GHz. After coating, the dielectric loss of PI - CM is 0.007. The dielectric loss of the composite membranes containing PTFE is between 0.001 - 0.009. For instance, the dielectric loss of CM - 30% at 10 GHz is merely 0.001, meeting the requirements of practical applications. The dielectric breakdown strength ranges from 108 - 169 kV mm−1. The CM - 20% sample has the highest dielectric strength, reaching 169.44 kV mm−1, and the dielectric strength of the PI - CM membrane is 108 kV mm−1. The addition of PTFE and the coating treatment enhance the dielectric strength of the composite membrane.

(5) Surface Wettability and Water Absorption: The composite membranes perform impressively in surface wettability and water absorption. CM - 20% and CM - 40% display hydrophobic properties, with water contact angles reaching 92.2° and 110.8° respectively (refer to Figure 5). As the PTFE content in the composite membrane increases, the water absorption is remarkably improved. The CM - 40% has the lowest water absorption, only 0.5%. This is of great significance for dielectric materials used in specific humid environments as it can effectively mitigate the impact of moisture on material performance.

II. Conclusion

This study successfully prepared nanofiber membranes composed of polyimide (PI) and polytetrafluoroethylene (PTFE) via an electrospinning machine. Nanocomposite membranes were then fabricated by dip - coating with a 10% polyamic acid (PAA) solution, followed by an imidization treatment. The resulting PI/PTFE@PI nanocomposite membranes exhibit outstanding dielectric properties, excellent thermal stability, low water absorption, enhanced mechanical properties, and remarkable abrasion resistance.

Specifically, the dielectric constants of PI - CM and the composite membranes range from 1.24 to 2.00, and the dielectric losses range from 0.008 to 0.071 in the 8.2 - 12.4 GHz frequency range. The dielectric breakdown strength ranges from 108 to 169 kV mm−1. The introduction of a customized coating structure significantly boosts the dielectric strength of the membranes. Additionally, the electrospun composite membranes made from a PAA - PTFE mixture show excellent hydrophobicity, with a contact angle of 110.8° and an extremely low water absorption of 0.5%. The CM - 20% variant has a tensile strength of 26.8 MPa, further demonstrating the mechanical robustness of the membranes. Thermal analysis reveals that these membranes possess high thermal stability, with a maximum thermal degradation temperature (Tmax) ranging from 641 to 659°C and a 5% weight loss decomposition temperature (Td5%) ranging from 407 to 450°C. These results highlight the potential of PI/PTFE@PI composite membranes as promising candidates for high - performance applications in the telecommunications field, especially in high - frequency environments.

Article Source: https://doi.org/10.1016/j.coco.2025.102367