Surface Potential and Zeta Potential Measurement via Sliding Drop Electrification

Surface potential and zeta potential are critical in understanding surface interactions in solid-liquid systems. Traditional methods, such as streaming potential or electrophoresis, are often limited by low precision, high cost, and dependency on specific assumptions. These challenges hinder reliable characterization of materials, particularly under diverse conditions such as varying pH or high salt concentrations. The spontaneous charge separation of moving liquid drops, an effect observed during sliding or dewetting, offers a promising avenue for surface characterization. However, existing techniques lack the precision to quantify this effect directly or translate it into reliable surface property measurements.

The technology measures surface potential and zeta potential by exploiting the charge separation that occurs when a liquid drop slides over a hydrophobic surface placed on a grounded metal plate. As the drop moves, it collects charge and leaves an opposite charge on the surface. This process is called slide electrification.

Key parameters are carefully chosen for accuracy (Fig. 2). The slide length ensures charge saturation, balancing drop size and transfer efficiency. The inclination angle (20°–70°, typically 50°) provides stable motion by gravity without disrupting charge separation. Drop volume (0.5–5 mm) affects contact line area and signal strength. Substrate properties like hydrophobicity and dielectric constants influence charge retention; coatings like PFOTS enhance reproducibility. Electrode placement captures the drop's charge at the end of the path, and a quantitative model converts the signal into precise surface potential values incorporating Debye length, dielectric constants, and electrostatic potential equations. This enables precise conversion of measured signals into surface potential values, providing a highly accurate and reproducible method for surface characterization.

• High Precision: Direct measurement of surface potential and zeta potential using advanced electrode technology.
• Cost-Effective: Reduces dependency on expensive and complex instruments like streaming potential analyzers.
• Broad Applicability: Works with various liquids, including polar and ionic solutions, and supports a wide range of surface chemistries.
• Simplified Setup: Utilizes basic components like inclined planes, reducing mechanical and operational complexity.
• Versatility: Suitable for single or multiple drop measurements, allowing optimization for different sample types and conditions.

• Material Science: Characterizing coatings, polymers, and functional surfaces.
• Chemical Engineering: Monitoring corrosion, catalysis, and electrochemical reactions.
• Biological Systems: Studying membranes, proteins, and other biointerfaces.
• Industrial Quality Control: Ensuring consistent surface properties in production processes.
• Energy Harvesting: Optimizing triboelectric nanogenerators using charge separation data.

EP23211526.1, 22.11.23

• Bista, P., Ratschow, A. D., Butt, H. J., & Weber, S. A. (2023). High voltages in sliding water drops. The Journal of Physical Chemistry Letters, 14(49), 11110-11116.
• Bista, P., Ratschow, A. D., Stetten, A. Z., Butt, H. J., & Weber, S. A. (2024). Surface charge density and induced currents by self-charging sliding drops. Soft Matter.