Electrospinning of nanofibers: Analysis of diameter distribution and process dynamics for control

Electrospinning employs electrostatic force to stretch a charged polymer solution jet and is capable of producing submicron diameter fibers. There has been considerable interest in electrospun fibers due to the ease with which nanometer-scale fibers can be produced from a wide range of polymers. In many applications, the average electrospun fiber diameter and its uniformity have important implications for the product's performance and process economics. Thus, it is desirable to develop electrospinning capability to achieve consistent and controllable fiber diameters. However, the current state-of-the-art electrospinning process results in varying diameter both during a run and runto-run. In addition, the relations of the process and material parameters to the resulting fiber diameter characteristics are not completely understood.;This research focuses on understanding what determines the fiber diameter distribution and developing the knowledge base for design of a fiber diameter control system in order to achieve a consistent and repeatable process.;The effects of operating parameters on process variability and resulting fiber diameter distribution are investigated. Different operating regimes are determined based on the Taylor cone behaviors and fluctuations. A minimal jet fluctuation regime is identified which helps select appropriate operating conditions.;The role of solvent evaporation in fiber spinning process is analyzed. Fiber diameter becomes smaller when solvent evaporation happens more slowly. The effect of ambient humidity on fiber formation by using aqueous PEO solutions is studied. For aqueous PEO solutions, the relative humidity is found to significantly affect fiber diameters and formation.;The correlations between several measurable variables such as straight jet diameter and bending angle to the resulting fiber diameter are established and able to predict the resulting fiber diameter.;The fundamental process dynamics are identified by step responses. An electrohydrodynamics model is developed to understand the fluid cone-jet and electric current dynamics as well as provide the basis for developing a measurement-based fiber diameter control system.