Abstract:

Significance Electrospinning technology has been widely used to produce a variety of nanofibers due to its ease of operation, compatibility with a wide range of polymers, and ability to control fiber morphology and dimensions. However, conventional electrospinning relies primarily on syringes and needles as spinnerets, resulting in low fiber yields and limited scalability. Currently, there are two main types of electrospinning technologies capable of large-scale nanofiber production: needleless electrospinning and air-assisted electrospinning. Both methods have received extensive research attention. Although needleless electrospinning has been extensively discussed in previous literature, there is a lack of summaries on air-assisted electrospinning techniques. Therefore, it is crucial to review the development status of air-assisted electrospinning technology to improve the large-scale production capabilities of electrospun fibers.

Progress Over the past decades, many studies have been devoted to improving the productivity of electrospinning for nanofiber production. Two main types of electrospinning technologies have potential for the mass production of nanofibers: needleless electrospinning and air-assisted electrospinning, each with its advantages. The latter offers increased productivity and refined fiber diameters. Introducing airflow into the electrospinning process creates additional forces on the jet that not only increase jet stretching and redirect the jet path, but also accelerate fiber solidification. As a result, fiber formation is accelerated, fiber diameter is reduced, and a unique fiber morphology is formed. These innovative changes also alter the fiber deposition location and fiber aggregation states, providing unique benefits. The airflow can be integrated in several directions, such as parallel, vertical, and reverse to the initial jet motion. Despite the difference in airflow direction, they all contribute to increased jet or fiber elongation. Various air-assisted electrospinning setups have been documented, including those based on traditional needle-based and state-of-the-art needleless electrospinning setups. Aerodynamic electrospinning has been developed using near-field induction to generate the jet and high-speed airflow to redirect the jet deposition. In combination with an air amplifier, electrospinning allows the trajectory of the jet to be manipulated. In addition, air can be incorporated into electrospinning by introducing it into the spinning solution to form bubbles, a technology also known as bubble electrospinning. The large curvature of the solution bubbles induces the generation of multiple jets, which increases nanofiber production. Centrifugal electrospinning is another air-assisted variant in which the airflow is passively generated by the high-speed rotation of the spinneret. The centrifugal forces combined with the electric field and airflow enhance the fiber production process. These innovative designs create opportunities to increase nanofiber production and provide unprecedented control over final product performance for a variety of applications. However, despite significant advances in this area, the technology is still in its infancy and requires further advances in both practical applications and theoretical understanding.

Conclusion and Prospect This review provides an overview of the current research situation in air-assisted electrospinning, including a brief history of its development, basic concepts, different spinning equipment designs, parameter effects, and modeling simulations. Air-assisted electrospinning is rapidly emerging as a viable approach for the production of large-area nanofibers. Previous research has resulted in unique designs based not only on needle-based and needleless electrospinning approaches and centrifugal spinning but also on breakthrough bubble dynamics. The ability to adjust fiber packing density through air flow opens up a viable way to manipulate nanofiber performance. Despite the remarkable progress, air-assisted electrospinning still faces challenges, particularly in precisely controlling the air-jet interaction and solvent evaporation during the electrospinning process, given the instability of the jet and the complexity of the polymer solutions. Despite many novel designs, the diversity in structure and shape of electrospinning nozzles still leaves many areas that are not well understood. These require further advances in experimentation and design. In addition, the harmonious blending of airflow and electric field forces has been a critical yet challenging aspect of air-assisted electrospinning. The theoretical understanding of the intricate interplay between aerodynamics and electric field during high-speed jet dynamics remains a mystery, particularly to the rapid drying mechanism influenced by the combined effects of airflow and electric field force. The lack of repeated validation by multiple research groups casts a shadow of doubt on the applicability of the existing findings, underscoring the need for further validation. The application potential of nanofibers produced by air-assisted electrospinning in various fields has yet to be fully realized. These challenges and uncertainties call for future research and development. It is expected that continued efforts in this particular field will lead to a deeper understanding of the underlying principles and mechanisms, which will ultimately lead to the optimization of nanofiber production techniques. As a result, air-assisted electrospinning is poised to revolutionize the field of nanofiber manufacturing, providing new opportunities for innovation and impacting various industries.

Key words: airflow assistance, electrospinning, nanofiber, productivity, spinneret