Predicting Operating Rules for Successful Melt Electrowriting

This communication predicts the previously undocumented "operating space"for melt electrowriting (MEW) of polycaprolactone as a model linear homopolymer by demonstrating the relative importance of viscous and elastic effects against surface tension-driven instabilities. It was shown that the polymer has a critical molecular weight of Mw,c ≈ 16,900 Da above which the manifestation of entanglement effects resulted in a noticeable change in the fiber morphology and a significant inflection point in the increasing melt viscosity. Calculations of dimensionless viscosity and elasticity, named Ohnesorge (Oh) and Deborah (De) numbers, respectively, suggested that the elasticity played a significant role in the stabilization of the melt electrospun jet, while no specific role of viscosity was directly noticed. In particular, our results showed that the requirements for the successful MEW of structures with minimum irregularities were De > 6 and number of entanglements greater than 3. In addition to identifying the correlation between the fiber morphology and melt rheological properties, the findings of this study may be used to predict the outcome of untested linear thermoplastics in the MEW process.