Measuring the streaming potential is an established electrokinetic method for characterising the surfaces of solid materials in contact with electrolyte solutions. If a liquid is moved along a solid surface under defined pressure, the charge carriers present in the electrical double layer shift, resulting in a measurable electrical voltage. The zeta potential, which is a key parameter for surface charge, wettability and interactions at interfaces, can be derived from the relationship between the applied pressure and the generated voltage.

The automated electrokinetic streaming potential analyser EKA 100 from Anton Paar is used to determine such zeta potentials of solid samples. The device works with pressure-controlled flow cells in which an electrolyte solution flows through the sample in a defined manner. The pressure is generated by a mechanical pump that provides discrete pressure stages up to a maximum differential pressure of around 500 mbar. The associated pressure-voltage relationship is recorded point by point, which ensures precise recording of the measurement data.

The evaluation is based on the gradient of the measured voltage as a function of the applied pressure, from which the zeta potential is calculated via ΔU/Δp. Different measuring cells are available for different sample geometries. Flat samples can be analysed in a flow cell with an adjustable gap, whereby gap widths of up to 0.10 mm can be realised. Alternatively, a cylindrical tube cell can be used for the analysis of membranes or fibre samples. To improve the accuracy of the results, the pH value and the conductivity of the electrolyte solution can be entered during the measurement and used to correct the calculated zeta potential.