Using Moving Electrode Impedance Spectroscopy to Monitor Particle Sedimentation

We have devised a method that employs moving electrode electrochemical impedance spectroscopy to monitor the sedimentation of particles in conductive suspensions. In contrast to standard electrochemical cells with a fixed geometry, our cell has a flexible design with a movable counter electrode that allows precise adjustment of the electrode distance. Measuring the electrical impedance at various electrode spacings and utilizing the linear dependence of this function on the electrode displacement enables probing of a small section of the sample. This has considerable advantages when heterogenous liquids (e.g., suspensions) are to be analyzed. We applied our moving electrode approach to various test cases and obtained the following results: (i) We demonstrated by experiment that the bulk conductivity can be measured correctly even if particle sediments cover the electrode surface. (ii) We studied monodisperse suspensions of various compositions and investigated the effect of particle concentrations and size on conductivity. (iii) We monitored the particle sedimentation process and, by combining experimental and theoretical results, identified a correlation between the growing mass of the sedimentation layer and the impedance measured. The intended application of our approach is to monitor crystallization processes in ionic liquids for use in zeolite synthesis.