Characterization of non-aqueous dispersions of carbon black nanoparticles by electrochemical impedance spectroscopy

Understanding fundamental electrochemical characteristics of industrial fluids, lubricants and their contaminants will allow for improvements in monitoring the performance of existent, and the formulation of new advanced industrial fluids and lubricants. This study focusses on the electrochemical characterization of model systems of colloidal dispersions of carbon black (CB), validation of these models, and investigation of applications of electrochemistry for determining the relative effectiveness of dispersants. Utilizing electrochemical impedance spectroscopy (EIS) analysis of industrial colloidal dispersions, an experimental method was developed to study the mechanism of dispersant/carbon black interactions, and the role of these interactions in the formation and stabilization of colloidal dispersions. Experimental EIS parameters such as conductivity, permittivity, critical frequencies of impedance and modulus relaxations, and impedance and modulus values were used in modeling equations describing particle sizes and interaction mechanisms occurring in CB dispersions. Results from the modeling equations show that dispersant micelles averaging 9 nm in diameter were present in solution. The dispersant micelles have a tendency to aggregate and form a loose “network”. In solutions containing CB, dispersants surround CB particles and form a colloidal suspension. An increase in relative concentration of the dispersant leads to a better stability of the suspension and prevents CB agglomeration. The diameter of the suspended CB particles decreases with added dispersant until a stabilization point is reached at approximately 200 nm. The validity of the impedance data and results of the modeling equations were confirmed by other analytical techniques, such as quasi-elastic light scattering and adsorption analysis.