Impedance spectroscopy interpretation of silica and polystyrene colloidal suspensions

Impedance spectroscopy differences between colloidal 295-nm silica and 300-nm polystyrene nanoparticles in deionized water are analyzed in this work. Using two different two-electrode measurement setups, designed for this application, impedance spectroscopy measurements performed directly in the colloidal suspensions with same nanoparticles size, shape and concentration, are fitted using Randles circuit models. The parameter analysis allows to identify the suspension response, the electrode-suspension interfaces response and nanoparticle double layer response. The first measurement system consists of a two aluminum wire electrodes characterized in a frequency range from 0.1Hz to 100 kHz while the second system was two square stainless steel electrodes characterized from 0.1Hz to 5 MHz. According to the results, polystyrene nanoparticles suspension presents higher conductivity and higher values of capacitance than silica suspension. It is revealed that as the nanoparticle concentration decreases, the suspension conductivity decreases for both colloidal suspensions. On the other hand, the electrode polarization effect contributed with high impedance and capacitance values, but showed a contrary behavior with the variation of the nanoparticles concentration. These differences found mainly arise because of the hydrophilic and hydrophobic nature of the silica and polystyrene nanoparticle surfaces.