Dewetting Film Dynamics Inside a Capillary Using a Micellar Nanofluid

An experimental study was performed in which hexadecane was displaced by a micellar nanofluid in a glass capillary. Experiments have shown that a thick film was formed on the capillary wall after hexadecane was displaced by the nanofluid. The thick hexadecane film is unstable, and over time it breaks and forms a thin film. Once the thick film ruptures, it retracts and forms an annular rim (liquid ridge) that collects liquid. As the volume of the annular rim increases over time, it forms a double-concave meniscus across the capillary and dewetting stops. The thin film on the right side of the double-concave meniscus then breaks and the contact angle increases. The process repeats until the droplets build up all along the capillary wall. Finally, the droplets are displaced from the capillary wall by the nanofluid and spherical droplets appear inside the capillary. This is a novel phenomenon because we did not observe any film formation when we used a solution without micelles. The theoretical model based on the lubrication approximation using the capillary pressure gradient was developed to estimate the annular rim dewetting velocity. The predicted dewetting velocity is found to be in fair agreement with the experimentally measured value.