The Leibniz Institute for Polymer Research in Dresden has successfully validated the measurement results of DataPhysics Instruments’ ZPA 20 zeta potential analyser. The long-standing cooperation between the measuring instrument manufacturer and the institute has ensured that the measuring system meets the highest quality requirements. The bidirectional, oscillating measurement method used by the system is patented and allows high-quality data sets in shortest measurement times.
The zeta potential is a measurable quantity that characterises the charge situation at a solid surface in solution. It is measured at the boundary between the ion layer firmly adsorbed on the solid surface and the solution. Dr. Astrid Drechsler, a scientist at the Leibniz Institute for Polymer Research Dresden e.V. (IPF), and an expert in the characterisation of polymer interfaces, explains why the zeta potential is an important parameter, “When a solid surface is submerged in an aqueous solution, it becomes electrically charged due to dissociable surface groups and adsorption of ions and molecules. The zeta potential provides information about these chemical functionalities and charge formation processes. Thus, it can be used to, for example, predict interactions such as adhesion between different surfaces.” Zeta potential measurements are important in a broad range of applications, such as the investigation of fuel cell membranes, fouling processes of filter membranes, bacterial growth on food packaging, and washing of textiles.
Depending on the size and shape of the samples, the zeta potential can be determined using different measurement techniques. For small particles in the nanometre to low micrometre range, electrophoretic methods are often used. For larger samples in the millimetre and centimetre range, the analysis of the streaming potential or the streaming current has proven to be advantageous. The new ZPA 20 zeta potential analyzer from DataPhysics Instruments uses a patented method based on the streaming potential and streaming current analysis. It is therefore particularly suitable for the investigation of samples in the macroscopic range. The device can be equipped with the MC-ZPA/S, a measuring cell for solid materials such as plates, membranes, or foils, and the MC-ZPA/PF, a measuring cell for fibres, powders and granulates.
Customers who are unsure whether the ZPA 20 zeta potential analyser is the right device for them can not only rely on the in-depth knowledge of the DataPhysics Instruments’ team, but also request trial measurements with their samples. Dr. Sebastian Schaubach, Chief Innovation Officer at DataPhysics Instruments, says, “Our laboratory offers contract measurements for all possible applications, with the ZPA 20 as well as all other devices of our portfolio.”
Since 2017, Drechsler and her team have accompanied the development of the ZPA 20 zeta potential analyser through several project phases. “In the first phase, we validated data measured with the prototype of the zeta potential analyser,” says Drechsler. A second project phase enabled further improvements of not only the device but also its measuring cells. “The focus was simplifying the handling of the measuring cells and achieving reproducible sample preparation,” explains Anja Caspari, a chemical laboratory technician at the IPF.
The streaming potential analysis for investigating the zeta potential works as follows: an electrolyte solution is pumped through a measuring cell containing the sample material. Specifically, it is pumped between two flat solid samples or through the gaps in fibre or powder packages. The flow of the electrolyte solution separates ions near the surface and carries them with it. This results in a difference in potential between the electrodes situated at both sides of the sample. Electrodes measure these differences, depending on the experiment, as streaming current, or streaming potential. These values, together with the pressure difference in front of and behind the measuring cell, allow the calculation of the zeta potential.
The ZPA 20 zeta potential analyser uses a patented measuring method to achieve rapid results with high accuracy. Schaubach explains, “The ZPA 20 zeta potential analyser measures the streaming potential or streaming current in a bidirectional and oscillating fashion.” The electrolyte solution is pumped over or through the sample not only in one direction but alternately in opposite directions. Additionally, the flow rate of the electrolyte liquid changes within every repeated cycle, resulting in pressure changes. The device records up to 100 pressure values together with the corresponding streaming potential or streaming current in one second. Thus, results with excellent statistical quality are generated within a short time frame. The software can easily process large amounts of data and evaluate them automatically.
The measuring method saves time during the measurements and also helps to reduce common sources of error. The oscillating measurement creates both positive and negative pressure differences, and consequently positive and negative values of the streaming potential or current. This may prevent the polarisation of the device electrodes.
Additionally, the bidirectional flow can reveal asymmetries of the sample surface, such as, for example, inhomogeneous fibre or powder packages as well as insufficiently fixed flat samples. Therefore, with the oscillating, bidirectional flow of the electrolyte, error sources can be identified and measurement errors prevented.
“The cooperation with the IPF helped us to tailor the ZPA 20 zeta potential analyzer to the needs of our customers right from the start and to design it with the highest scientific standards in mind,” says Schaubach, “We are especially proud that the patented measurement method renders zeta potential measurements quicker, easier and more reliable than ever before.”