The formation of nanofibers from electrospinning process.

摘要

It is well known that a charged surface becomes unstable when electrical forces overcome the force from surface tension. As the electrical potential rises, the surface droplet becomes nearly conical and a fine jet flows from the vertex. The process of electrospinning may be considered in two parts, the creation of the jet by distortion of a drop and the continuous flow of the jet. There are two electrical forces that act on the jet. The electrical force from the external field pulls the jet toward the target. The self repulsion of the charge carried by the jet makes each element of the jet grow longer. The self repulsion of the charge carried by jet drives the bending instability and, in a different way, drives splitting instability. Both instabilities can be observed with a high frame rate camera.; A mathematical model was developed to calculate the three-dimensional path of the jets. The movement of the jet and the growth of bending instability were measured experimentally and compared to calculations from the model. The bending instability makes it possible for the length of the jet, measured along its axis, to increase by a factor of around 100,000, in the space between the droplet and the target that is only a few tens of centimeters long. When the jet is bent into many circles, the total perimeter of all the circles increases more rapidly than the diameter of the circles. The bending instability is a self-similar process that repeats at smaller and smaller scales, so the large elongation can be accommodated easily. Most of the above observations were made in solutions of polyethylene oxide in water, poly(2-hydroxyethyl methacrylate) in a mixture of ethanol and formic acid and polystyrene in a mixture of toluene and dimethyl formamide. The growth of the bending instability depends strongly on solution concentration. Jets with larger diameters, from the more concentrated solutions tended not to bend, but instead, to develop smaller jets with paths nearly perpendicular to the primary jet, which we call a splitting instability. At lower concentrations, the bending and splitting occurred simultaneously.