Alberto Ramon

Near‐field electrospinning (NFES) enables producing two‐ and three‐dimensional patterns and objects with submicrometric features by the controlled positioning of an electro‐hydrodynamically emitted fiber on a collector. To realize the high‐resolution potential of NFES, matching the jet arrival speed to the intended printing speed is essential. In this work, we use electrostatic jet deflection (EJD) to determine how the jet speed and characteristics of the collected fiber depend on the ink properties, ambient conditions, and processing parameters. We observe that the jet speed increases with higher applied voltages and lower nozzle‐to‐collector distances owing to the increase in electric field strength. It also increases with the ink’s electrical conductivity and preventing the drying of the drop. Slower jets are generated when using high‐viscosity inks or increasing the nozzle diameter, which promotes the ink drop drying at the nozzle exit. Fiber diameter is affected by the evaporation of the solvent on the drop surface, and it can be increased when raising the polymer concentration in the ink. Overall, we take advantage of the availability of EJD for determining the jet speed, enabling us to produce high‐resolution patterns by NFES while demonstrating different procedures to tune the jet speed and fiber diameter.

Electrohydrodynamic (EHD) jet printing of solvent-based inks or melts allows for the producing of polymeric fiber-based two- and three-dimensional structures with sub-micrometer features, with or without conductive nanoparticles or functional materials. While solvent-based inks possess great material versatility, the stability of the EHD jetting process using such inks remains a major challenge that must be overcome before this technology can be deployed beyond research laboratories. Herein, we study the parameters that affect the stability of the EHD jet printing of polyethylene oxide (PEO) patterns using solvent-based inks. To gain insights into the evolution of the printing process, we simultaneously monitor the drop size, the jet ejection point, and the jet speed, determined by superimposing a periodic electrostatic deflection. We observe printing instabilities to be associated with changes in drop size and composition and in the jet’s ejection point and speed, which are related to the evaporation of the solvent and the resulting drying of the drop surface. Thus, stabilizing the printing process and, particularly, the drop size and its surface composition require minimizing or controlling the solvent evaporation rate from the drop surface by using appropriate solvents and by controlling the printing ambient. For stable printing and improved jet stability, it is essential to use polymers with a high molecular weight and select solvents that slow down the surface drying of the droplets. Additionally, adjusting the needle voltages is crucial to prevent instabilities in the jet ejection mode. Although this study primarily utilized PEO, the general trends observed are applicable to other polymers that exhibit similar interactions between solvent and polymer.