ELECTROHYDRODYNAMICS OF ELECTROSPINNING PROCESS

Alexandre F. Spivak
Department of Engineering Mechanics
University of Nebraska - Lincoln
Lincoln, NE  68588
Advisor:  Professor Yuris Dzenis

Date: Thursday, December 7, 2000
Time: 3:30 p.m.
Place: W106 Nebraska Hall


The emerging technology of manufacturing of polymer nanofibers by electrospinning is addressed in this dissertation. Rapidly growing interest in the electrospinning process is based on a large number of current and potential applications of polymer nanofibers. In spite of a clear need for theoretical models for better process control and optimization, the bulk of the electrospinning research to date has been empirical by nature. From the electromechanical point of view, electrospinning is a process of elongational flow of a charged polymer jet that is stretched by intensive electric forces. The main stages of the process are jet initiation, steady state spinning, and jet instabilities. Analytical models of these three stages are developed in this dissertation. The jet initiation is treated as a problem of shape evolution of a charged liquid meniscus held by surface tension. The criterion of jet initiation is formulated. The steady state spinning is analyzed and a governing equation for the steady state jet is derived. Non-linear rheological properties of the polymer fluids are incorporated in the electromechanical model for the first time. Stability of a rectilinear jet is analyzed by modeling jet radius fluctuations. An equation for the critical initial jet radius is derived. A model of bending instability is formulated taking into account viscoelastic properties of a polymer fluid. Governing equations for viscoelastic jet bending are derived. Kinetics of hierarchical bending instabilities is analyzed for the first time. Experimental observations of the electrospinning process corroborate the theoretical models. Experimental observations and the results of modeling indicate the importance of the electrospinning process zone beginning at the point of the first instability and extending to the nanofiber collector. Preliminary experimental analysis of the composition of the process zone is performed and reported.