Experimental Assessment of Charge Flow in Electrospinning
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Electrospinning is a method of using high voltage electric fields to transform polymer solutions into nano-scale fibres. The field has seen significant work on processing different polymers and their resulting fibres but less work has focused the electrospinning process itself. The aim of this thesis is to present experimental observations of charge behaviour in the electrospinning process in the context of the underlying physics typically used to describe electrospinning. This thesis presents a review of existing methods of measuring aspects of the electrospinning process, and reviews published mathematical models of the process as representative examples of the current understanding of the underlying physics that drive the electrospinning phenomena. A novel measurement technique is introduced - high frequency data capture of the electric current flow simultaneously at the high voltage and collector electrode. This is used in three ways: to examine bulk charge density, to measure fibre flight time, and to quantify charge lost from the fibre in flight. Charge density is studied by comparing current and mass flow at the Taylor cone under a wide range of conditions. For 8% PVOH in water a constant bulk charge density was found of 7.7 C/kg. Flight time is studied by determining the time from the application of high voltage to the charged fibre first arriving at the collector electrode. It was found that for 8% PVOH the flight time depended strongly on applied voltage while electrode distance had a negligible effect. Charge loss was studied by comparing the magnitude of the simultaneous current flows in the quasi-steady state to determine if the charge flowing into the Taylor cone arrives with the fibre at the collector. For 8% PVOH, 8% PVOH with ionic salt, 9% PVOH in water and 18% PVB in ethanol, it was found that charge is always lost.