On the mechanism of jet splitting in electrospinning

Electrospinning from drops containing polymers is widely used to produce fibers of different morphologies with various applications in tissue engineering, filtration, energy, biotechnology and sensors, and efforts have been made to understand the associated instabilities. The fiber diameter can be reduced to an extent with solution properties and primarily through jet instabilities like branching whipping and jet splitting. We unravel the dynamics of jet splitting in electrospinning using ultra-high-speed stereo imaging. Experiments were conducted over a wide range of molecular weights of the PEO polymer. Taylor jets start for an electric field above 2800 V/cm, while above 3500 V/cm, the jet flattens, and sideways branching occurs. But branching only occurs when the collector is significantly wider than the nozzle. In a particular range of molecular weights, holes nucleate at the base of the branch. These holes rapidly expand and split into two subfilaments. The same splitting mechanism occurs for the tertiary jets to reduce the fiber diameter by an order of magnitude. For the largest molecular weight polymer solutions, we observe ‘fractal-type branching’.