Electrospinning Equipment: Effects of Concentration & Voltage on Nylon 6 Nanofiber Membrane

Nylon 6 nanofiber membranes have garnered significant attention due to their exceptional mechanical strength, high porosity, and large specific surface area. These membranes are typically manufactured using conventional techniques such as melt spinning, dry spinning, and wet spinning. However, electrospinning stands out for its high manufacturability and broad application potential. As a widely used thermoplastic polymer, Nylon 6 has demonstrated considerable potential in various fields, including energy, environment, and biomedicine, where it can be utilized as battery separators, filtration materials, and tissue engineering scaffolds.

Despite these promising applications, Nylon 6 nanofiber membranes face several challenges, such as chemical and mechanical degradation, toxicity, non-biodegradability, difficulty in recycling, high production costs, and a propensity for clogging. To address these issues and optimize the performance of these membranes, researchers have employed electrospinning to tailor the physicochemical properties of the fibers to meet specific application requirements. However, theoretical investigations into the electronic properties of Nylon 6 nanofiber membranes remain limited. Therefore, this study not only experimentally explored the physicochemical properties of Nylon 6 nanofiber membranes but also conducted theoretical analyses of their electronic properties using Density Functional Theory (DFT) to provide theoretical support for further development and application of this material.

1. Research Findings

1. 1 Electrospinning of Nylon 6 Nanofiber Membranes

In this study, Nylon 6 nanofiber membranes were successfully fabricated via electrospinning machine. The researchers dissolved Nylon 6 pellets in a mixture of acetic and formic acids to prepare solutions of varying concentrations (14 wt%, 16 wt%, and 18 wt%). These solutions were loaded into a syringe and subjected to high voltage (20 kV or 25 kV) through a nozzle, stretching the solution into ultrafine fibers that were deposited onto an aluminum foil-covered collector to form the nanofiber membrane. By precisely controlling parameters such as solution concentration, voltage, and the distance between the nozzle and the collector, the researchers were able to regulate the diameter and morphology of the fibers, successfully producing uniform Nylon 6 nanofiber membranes. The results showed that a 14 wt% Nylon 6 solution at 20 kV could form uniform ultrafine nanofibers without bead or spider-web-like structures (as shown in Figure 1).

Figure 1. SEM images of electrospun Nylon 6 nanofibers at different concentrations and voltages: (a) 14 wt% @ 20 kV, (b) 16 wt% @ 20 kV, (c) 18 wt% @ 20 kV, (d) 14 wt% @ 25 kV, (e) 16 wt% @ 25 kV, and (f) 18 wt% @ 25 kV, along with their respective fiber diameter size distributions (nm).

1.2 Influence of Concentration and Voltage on Fiber Diameter

The study revealed that the diameter of the electrospun fibers was directly proportional to the solution concentration and slightly decreased with higher applied voltage. Specifically, as the concentration increased from 14 wt% to 18 wt%, the fiber diameter rose from 73.34 nm to 85.00 nm at 20 kV. When the voltage was increased from 20 kV to 25 kV, the fiber diameter slightly decreased, for example, from 73.34 nm to 72.12 nm for the 14 wt% solution. This demonstrated that adjusting the solution concentration and applied voltage could effectively control the fiber diameter (as shown in Table 1).

Table 1. Crystallite size and d-spacing of nanofibers at different concentrations and applied voltages.

1.3 Density Functional Theory (DFT) Analysis of Electronic Properties

DFT calculations indicated that the HOMO-LUMO band gap energy of the Nylon 6 molecule was 6.60 eV, signifying high kinetic stability (as shown in Figure 2). Additionally, the electronic chemical potential was -3.83 eV, indicating a strong electron-donating capability of Nylon 6. These characteristics suggest potential applications of Nylon 6 nanofiber membranes in electrochemical sensing and electronic devices.

Figure 2. Analysis of molecular orbitals and band gap energy of Nylon 6 molecules.

1.4 Molecular Electrostatic Potential (MESP) Analysis

MESP analysis identified the nitrogen atom of the amine group in the Nylon 6 molecule as a binding site for electrophilic attack. The MESP map showed that the nitrogen atom carried a positive charge, making it a favorable site for electrophilic reactions, while the oxygen atom in the carbonyl (C=O) group had a negative charge, rendering it susceptible to electrophilic attack (as shown in Figure 3). This charge distribution endows Nylon 6 nanofiber membranes with efficient charge transfer capabilities for applications in electrochemical sensing and electronic devices.

Figure 3. Molecular electrostatic potential (MESP) map of Nylon 6 molecules: (a) folded MESP; (b) unfolded MESP.

2. Conclusions

This study successfully fabricated Nylon 6 nanofibers via electrospinning machine. Using DFT, the Nylon 6 molecule was optimized, and its chemical descriptors, including HOMO-LUMO levels, ionization energy, and electron affinity, were calculated. The study found that a 14 wt% solution promoted the formation of uniform ultrafine nanofibers, eliminating bead and spider-web-like structures. The fiber diameter was directly proportional to the solution concentration and slightly decreased with higher applied voltage. When the applied voltage reached 25 kV, the fiber diameter decreased with increasing concentration. The thickness of the electrospun membranes diminished as the electrospinning voltage increased, making the production of such membranes more challenging. MESP analysis identified the nitrogen atom of the amine group as a binding site for electrophilic attack. The HOMO-LUMO band gap energy and global chemical reactivity characteristics of Nylon 6 indicated its kinetic stability. The results demonstrate that variations in concentration and applied voltage are crucial factors in altering the properties of electrospun nanofibers.

During the experimental research process, a user-friendly and high-precision electrospinning device is indispensable. The Weimai Multi-functional Electrospinning Machine E04, equipped with two sets of exclusive four-needle/eight-needle array nozzles, can simultaneously perform dual-component material spinning and multi-material coaxial multi-needle electrospinning to produce more complex fiber membranes. The integrated refrigeration and dehumidification system controls temperature and humidity to ensure optimal spinning conditions, preventing issues such as liquid spraying, droplet formation, and fiber hanging. The device can also control experimental time, record, save, and import historical experimental data.

Article Source: https://doi.org/10.1038/s41598-025-88356-y