Modeling of non-isothermal polymer jets in melt electrospinning

Abstract

We have developed a model for non-isothermal, free surface flows of electrically charged viscoelastic fluids in the stable jet region of the melt electrospinning process. The model is based on thin filament approximation applied to fully coupled momentum, continuity, and energy equations, Gauss’ law, and the non-isothermal Giesekus constitutive model. The asymptotic jet thinning relationship widely used in previous electrospinning models was found not applicable for the case of polymer melts. The underlying assumption of the balance of inertial and electrical forces in the asymptotic region does not hold for typical melts which exhibit high tensile forces throughout the spinning region, particularly under non-isothermal conditions. We have developed a new initial thinning condition for fluids with low electrical conductivity and high viscosity based on a force balance near the nozzle. The resulting system of equations is solved numerically and the simulated initial jet profiles are compared to digitized experimental images of the stable melt jet near the spinneret. In addition, the predicted effects of melt temperature, flowrate, and electric field strength on the final jet diameter are compared to the final average fiber thickness from non-isothermal experiments where the whipping motion has been suppressed by rapid cooling. The simulation results are in good quantitative agreement with the flow visualization experiments on electrospinning of polylactic acid (PLA) melt under various spinning conditions.