Interfacial tension measurement with force tensiometer

Force tensiometers are employed for measuring interfacial tension by gauging the forces exerted on a probe positioned at the liquid-liquid interface. This probe, connected to a highly sensitive balance, interacts with the interface, and the resulting forces are measured to calculate interfacial tension. Factors influencing the measured force include the size and shape of the probe, the contact angle between the probe and the liquid, and the interfacial tension between the liquids. Probes, typically made of platinum, are designed to maintain a zero degree contact angle with the liquid under study, with two common configurations being the du Noüy ring and Wilhelmy plate.

Interfacial tension measurement with Du Noüy ring and Wilhelmy plate

In interfacial tension measurements using the du Noüy ring, the denser liquid phase (e.g., water) is first immersed, followed by the less dense liquid (e.g., oil), while avoiding ring contamination. The measurement begins as the sample stage descends, and when the ring reaches the interface, the software detects it and continues until the force peaks and then drops. Measurement should progress from polar to dispersive liquids, with adjustments made if the denser phase changes (e.g., water becomes the less dense phase), termed the push mode. Density correction is automatically applied by the software.

Similarly, the Wilhelmy plate, another tool for interfacial tension measurement, involves a platinum plate interacting with the interface. However, compensating for buoyancy from the light phase is necessary. Despite its slightly more complex procedure, the du Noüy ring is favored for interfacial tension measurements due to its practicality.