(417h) Zeta Potential: A Neglected Parameter in the Characterization of Nanoparticulate Suspensions

Zeta Potential: A Neglected Parameter in the Characterization of Nanoparticulate Suspensions

David Fairhurst PhD and Patrick O’Hagan PhD

While particle size (distribution) has been long recognized as an important metric, the most fundamental and critical aspect, especially of nanoparticulate suspensions, is the molecular interaction between the suspended particles and the medium at the interface. It is such an interaction, along with the particle–particle interactions, that determines the dynamic properties of the dispersion and strongly affect the performance of the suspension.

The zeta potential (ZP) is a parameter (symbol ζ), which is related to the surface charge (vide the interfacial chemistry), a property that all materials possess, or acquire, when suspended in a fluid. The sign and magnitude of the ZP affect process control, quality control, and product specification; at the simplest level, the ZP can help maintain a more consistent product and at a complex level, it can improve product quality and performance. At the very least its measurement answers the question: Is the electrical charge on the material particle positive or negative? Such information is often sufficient to suggest further steps in formulation or processing. The next higher level of inquiry has to do with quality control: Has the product sufficient electrostatic repulsion (because of the magnitude of the surface charge) to maintain its stability?

            The ZP represents, in the practical sense, the effectiveness of the particle surface charge in solution.  While it may derive, initially, from the fundamental number of surface sites, (how many, what type, etc.), more importantly, from a practical application, are the solution conditions themselves, because they control the resulting final sign and magnitude of ζ.  The consequence of this to the process of dispersing particles is critical. And importantly, it is useless to quote a measured ζ value without specifying the suspension conditions under which the measurement was made.

            In this paper we will discuss the effect of ZP on suspension properties and present a variety of applications of ZP measurements to illustrate its practical broad utility and commercial significance.