A study on daughter droplets formation in bitumen/glass/water contact line displacement due to instability

Experiments were performed to study the displacement of a rectangular strip bitumen, coated on a glass plate, in the presence of water at different pH and temperature. During the displacement, modulated structure formed at the bitumen/water/glass contact line and ridge-like structure formed at the bitumen/water interface. The modulated and ridge structures formed due to the contact line and the free surface instabilities. These instabilities grew further, which led to the formation of daughter droplets. On the contrary, circular bitumen disk displaced uniformly in the inward radial direction to form single droplet in the presence of water. The number of daughter droplets formed increases with the decrease in the width of the bitumen strip for a constant strip length. It was observed that the number of daughter droplets increases with the increase in pH and temperature of water. The observed growth of instability and the experimental results were compared with the instability analyses on dewetting process available in the literature. It is recommended that a non-symmetrical shape of bitumen film on sand grain may be detrimental to bitumen separation in an oil sand extraction unit.