Solution electrospinning is a versatile and widely used technique for producing polymer and composite nanofibers with diameters ranging from tens of nanometers to several micrometers. The process involves the application of a high-voltage electric field to a polymer solution, which overcomes surface tension and elongates the solution into ultrafine fibers that are deposited onto a grounded collector. This method is particularly advantageous for creating high-surface-area materials with tunable morphologies, making them suitable for applications in filtration, energy storage, and other advanced technologies.

The electrospinning setup consists of three primary components: a high-voltage power supply, a syringe or capillary tube containing the polymer solution, and a grounded collector. When a high voltage is applied, the electric field induces charge separation in the polymer solution, forming a Taylor cone at the tip of the needle. As the electric force overcomes the surface tension of the solution, a charged jet is ejected and undergoes whipping instabilities, leading to significant stretching and thinning of the fiber. The solvent evaporates during this process, leaving behind solid nanofibers on the collector.

Key parameters influence the morphology, diameter, and uniformity of the electrospun nanofibers. These include solution properties, processing conditions, and environmental factors. Among the most critical parameters are voltage and solution viscosity.

Voltage plays a pivotal role in determining fiber diameter and morphology. Typically, voltages between 5 kV and 30 kV are applied, depending on the polymer-solvent system and the desired fiber characteristics. At low voltages, the electric field may be insufficient to overcome surface tension, resulting in droplet formation rather than fiber formation. As voltage increases, the jet experiences greater stretching forces, leading to thinner fibers. However, excessively high voltages can cause instability in the jet, leading to bead formation or irregular fiber diameters. Optimal voltage must be determined empirically for each polymer-solvent combination.

Solution viscosity is another crucial parameter, directly influenced by polymer concentration and molecular weight. Low-viscosity solutions tend to produce beads or discontinuous fibers due to insufficient chain entanglement. Conversely, high-viscosity solutions yield thicker fibers or may even clog the needle, preventing jet formation. A moderate viscosity range ensures sufficient polymer chain entanglement for fiber continuity while allowing adequate stretching under the electric field. For most polymers, concentrations between 5% and 20% (w/v) are commonly used, but this varies with polymer type and solvent.

Other parameters affecting electrospinning include:
- Flow rate: Lower flow rates (0.1–2 mL/h) allow sufficient time for solvent evaporation, producing uniform fibers.
- Tip-to-collector distance: Distances between 10 cm and 20 cm are typical, balancing solvent evaporation and jet stability.
- Solvent volatility: Fast-evaporating solvents reduce bead formation but may require humidity control to prevent premature drying.
- Conductivity: Adding salts or conductive materials can enhance jet stability and reduce fiber diameter.

Electrospun nanofibers have found extensive use in filtration applications due to their high surface area, porosity, and tunable pore structure. These fibers are particularly effective in air and water filtration, where they can capture particulate matter, bacteria, and even nanoparticles. The small fiber diameters enhance interception and inertial impaction mechanisms, while the high porosity ensures low pressure drop across the filter. Composite nanofibers incorporating materials like activated carbon or metal-organic frameworks further improve filtration efficiency by adding adsorption capabilities.

In energy storage, electrospun nanofibers serve as electrodes and separators in batteries and supercapacitors. Their high surface area facilitates greater active material loading and improved ion transport, enhancing energy and power density. For lithium-ion batteries, electrospun carbon nanofibers provide conductive networks that improve charge-discharge kinetics. In supercapacitors, polymer-derived carbon nanofibers exhibit high electrical conductivity and porosity, enabling rapid charge storage and release. Hybrid nanofibers incorporating conductive polymers or metal oxides further enhance electrochemical performance.

Composite nanofibers expand the functionality of electrospun materials by incorporating nanoparticles, carbon nanotubes, or other polymers. These additives can impart mechanical strength, electrical conductivity, or catalytic activity. For example, adding silver nanoparticles introduces antibacterial properties, while graphene oxide enhances electrical conductivity for sensor applications. The distribution of additives within the fibers depends on their compatibility with the polymer matrix and the electrospinning conditions.

Despite its advantages, solution electrospinning faces challenges such as low production rates and scalability issues. Multi-needle setups or needleless electrospinning methods have been explored to increase throughput. Additionally, optimizing solvent systems for environmentally friendly processing remains an area of active research.

In summary, solution electrospinning is a powerful technique for fabricating polymer and composite nanofibers with precise control over morphology and composition. By carefully optimizing parameters such as voltage and viscosity, researchers can tailor fibers for specific applications in filtration and energy storage. Continued advancements in material formulations and process scaling will further expand the utility of electrospun nanofibers in industrial and technological applications.