Effect of inertia on the dynamic contact angle in oscillating menisci

The contact angle between a gas–liquid interface and a solid surface is a function of the dynamic conditions of the contact line. Classic steady correlations link the contact angle to the contact line velocity. However, it is unclear whether they hold in the presence of inertia and the case of perfect wetting fluids. We analyze by means of experiments the shape of a liquid interface and the corresponding contact angle in accelerating conditions for two different fluids, that is, HFE7200 (perfect wetting) and demineralized water. The setup consists of a U-shaped quasi-capillary tube in which the liquid column oscillates in response to a pressure step on one of the two sides. We obtained the evolution of the interface shape from high-speed back-light visualization, fit interface models to the experimental data to estimate the contributions of all the governing forces, and perform measurements of the dynamic contact angle. We propose a new model to account for the impact of the interface acceleration on its shape, and we discuss the impact on the measurement of the transient contact angle. The new model allows us to perform dynamic contact angle measurements below 15°, which is challenging to obtain with traditional techniques. We show for the first time a dynamic characterization of the wetting behavior of HFE7200, and we compare the results with traditional hydrodynamic models.