AbstractsBiology & Animal Science

Electrospinning and Nanofibers

by Tao Han




Institution: University of Akron
Department: Polymer Science
Degree: PhD
Year: 2007
Keywords: electrospinning; nanofibers; buckling instability; bending instability; pendulum-like motion
Record ID: 1805154
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=akron1197407558


Abstract

Electrospinning offers a unique way to produce submicron and nanofibers. It utilizes an electrical force to generate a fine, charged jet from the surface of a viscous liquid. This jet moves straight towards a grounded collector for a certain distance, then bends into spiral coils; finally, the jet solidifies and collects as nonwoven cloth. Determination of the jet path near the onset of the electrical bending instability is important for the orderly collection of the electrospun fibers. The onset and development of the electrical bending instability were investigated. Under certain conditions, high applied voltage prohibited the onset of bending instability and a straight jet reached the collector. Micron and submicron fibers were produced by collecting a straight jet on a moving collector. The diameter, velocity and the longitudinal stress along the jet axis of an electrospinning jet were measured using custom-built equipment. A new apparatus was designed to measure the longitudinal stress along the electrospinning jet. The relaxation of longitudinal stress along the electrospinning jet was experimentally verified. The elongational relaxation time and elongational viscosity of the polymer solution were characterized. Buckling instabilities of electrospinning jets were observed and compared with the behavior of uncharged jets. Various two-dimensional and three-dimensional micron size patterns were produced by the buckled electrospun fibers. A novel pendulum-like motion of a straightelectrified jet was observed and the resulting hierarchical structures made from buckled fibers were presented. A theoretical model was proposed and simulated results showed reasonable agreement with the experimental observations. This work extends the understanding of the complicated electrospinning process.