Methods for electrical impedance spectroscopy and tomography characterising particles in suspensions and crystallisation processes

Electrical impedance spectroscopy (EIS) is a method used to study the frequency dependence of the dielectric properties of colloidal suspensions by applying an alternating electric field. When an alternating electric field is applied, a dipole moment can be induced on a charged-particle due to the relative motion between the particles
and their electric double layer. The macroscopic display of induced dipole moment is usually represented by the impedance parameters, including the impedance real part,
imaginary part, phase angle and the relaxation frequency. These quantities are related to the size, shape and surface of the dispersed particles, the nature of the dispersed
medium, and also the concentration of the particles.

This thesis describes a fundamental study of the EIS method applied to colloidal particles. The relationship between the impedance parameters and the properties of
particle suspensions is investigated. The study reveals the effects of particle size, particle concentration and ionic concentration dependence on the detected impedance
parameters. Based on the study, new methods, including modelling, signal process, test set-up and data analysis, for characterisation of particles in suspensions are
developed through the experimental approach and theoretical analysis. The methods are verified with silica suspensions and applied to crystallisation processes. The online
measured electrical impedance spectra associated with L-glutamic acid nucleationgrowth processes and a polymorphic transformation are analysed. It is demonstrated
that the methods can be applied for on-line monitoring of the particle size and polymorphs in crystallisation processes. Electrical impedance tomography based on
EIS measurement conducted with different materials, including non-conductive plastic bar, banana, and silica suspensions are studied. The responses of electric polarisation of colloidal particles on tomographic images can be observed. However, the difference in particle size cannot be observed in the tomographic images possibly due to the limits of the imaging resolution from an 8-electrode sensor and the signal quality affected by the limits of the common mode voltage rejection ratio of the instrument.