Laboratory Products


Dynamic streaming potential analysis Carina Santner, Dr Thomas Luxbacher, Anton Paar GmbH


Zeta potential is a measure of the electrostatic interaction at the interface between a solid surface and a liquid medium. While electrophoretic light scattering enables the determination of zeta potentials for particles in a dispersion, streaming potential measurements serve as a tool for assessing the zeta potential on solid surfaces. The dynamic streaming potential is an extension of the classic streaming potential measurement and allows for real-time monitoring of the interaction between solutes and solid surfaces. This article aims to understand the principles of the dynamic streaming potential measurement and explores its various applications.


Introduction


Zeta potential is a key parameter in colloid science and electrochemistry. It is established on the surface of any material when it comes in contact with a liquid medium, typically an aqueous solution, and is thus an interfacial property. Put simply, it refers to the electric charge that exists on the surface of small particles when they are suspended in a liquid or on a solid surface that is surrounded by an aqueous solution.


Measuring the zeta potential helps us understand how surfaces perform, how well particles stay dispersed, and how solutes interact with solid surfaces. Knowing the zeta potential of macroscopic surfaces is important in applications like water treatment, creating materials for medical applications or formulating various cosmetic and detergent products. Understanding a material’s zeta potential helps to improve its surface for better performance.


In this article, we introduce the dynamic streaming potential, discerning its distinctions from the classic streaming potential, and elucidate the diverse range of applications that offers users a wide range of new possibilities.


Classic streaming potential


Streaming potential is a phenomenon that occurs in fl uid-fi lled capillaries or porous materials when there is relative motion between the fl uid and the solid surfaces [1]. Solid materials with a fl at surface are placed in a suitable measurement cell in a way to create a rectangular fl ow channel (Figure 1a).


Subsequently, the channel is fi lled with an aqueous electrolyte solution, typically a diluted salt solution. This leads to charge formation at the interface between the solid sample and the electrolyte solution. These charges are then compensated by oppositely-charged ions from the diluted salt solution.


When the measurement is started, a pressure gradient ∆p is applied to the electrolyte solution, inducing a fl ow through the capillary in the measurement cell, which is shown in Figure 1b. This movement causes the charges, which were established before at the liquid/solid interface, to travel with the fl ow.


Figure 1: (a) Schematic presentation of the formation of a rectangular fl ow channel between samples with a fl at surface. (b) Generation of streaming potential by liquid fl ow through a capillary channel enforced by a pressure gradient.


This results in an accumulation of charge carriers on one side of the measuring cell and a depletion on the opposite side.


A so-called streaming potential Ustr is generated along the fl ow channel. The measured streaming potential, in combination with the applied pressure, is then used to calculate the solid surface zeta potential Ustr of the sample.


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