Electrical Double Layers in Electrospray Propulsion

Ionic liquids, propellants in electrospray thrusters, cannot be described by classical dilute double layer theories; new theoretical frameworks have been introduced which predict multilayer double layer structures with different capacitance curves. These theories must be generalized to account for ion size asymmetry and be verified with experimental data. This work explores three different methods for measuring capacitance: cyclic voltammetry, impedance spectroscopy, and potentiostatic intermittent titration technique. All three methods gave qualitatively similar capacitance curves at moderate potentials, with a central hump and rising wings. Concentrated solution theories predict the wings to eventually decay, and this was seen in the impedance data as well as the positive wing in voltammetry.