Nanoscale Fiber Deposition via Surface Charge Migration at Air-to-Polymer Liquid Interface in Near-Field Electrospinning

In electrospinning, a liquid polymer meniscus deforms into a conical structure called the Taylor cone when an excessive electric field is applied to the air-to-polymer interface. This Taylor cone is electrohydrodynamically formed, and its apex ejects a microscale jet when a convective current dominates over the bulk current. However, when the convective current is negligible, and the surface current dominates over the bulk current, a new electrostatic microscale conical feature ("electrostatic" microcone) can be formed on the surface of the liquid polymer and emits a much lower jet flow rate than the Taylor cone. This study presents the deposition of nanoscale fiber by near-field electrospinning (NFES) and provides systematic studies for the formation of the electrostatic microcone, sub-microscale polymer jet from the microcone, and electrostatic characteristics of the polymer jet, which pertain to the jetting mechanism in NFES. Based on the understanding of the underlying mechanism of NFES, a jet profile model for the corresponding regime was developed, and its validity was examined with respect to nanofiber deposition e7eriments in the range 50-500 nm. In addition, the effect of solvent evaporation is discussed during the jetting process.