Spreading and shrinking behaviors of oil films with different viscosities on a cold immiscible liquid substrate

Abstract

The spreading behavior of an oil film on an immiscible liquid substrate plays an important role in practical phenomena such as oil spills and thermal spraying. Especially in extremely cold regions such as the Arctic regions, the spreading behavior and balanced state of the spilled oil may be significantly affected due to the varying oil physical properties caused by the low temperature. The effect of low-temperature conditions on the spreading behavior remains poorly understood. The spreading experiments of silicone oils with viscosities of 50, 100, 350, and 1000 cs were carried out on cold substrates by controlling the liquid substrate temperature in the range of − 20 °C to 20 °C through a circulating bath. The effects of substrate temperature on the spreading morphology, equilibrium thickness, spreading rate and other parameters of the oil film were investigated. When the temperature was greater than 10 °C, silicone oils spread continuously, whereas when the temperature was less than 0 °C, some of them first exhibited a short period of shrinking behavior before spreading. The surface tensions at three interfaces, namely oil–air, oil–substrate, and substrate–air, were analyzed comprehensively. A novel equilibrium equation of the gravity-surface tension based on Neumann’s triangle rule was derived to calculate the stable thickness of the oil film, in which the contact angle at the three-phase junction was measured experimentally, and the quantitative relationship between the surface tension and temperature was considered. The calculated results were in excellent agreement with the experimental results. A modified prediction model was fitted to accurately describe the spreading velocity of the silicone oil by considering the effect of temperature on the viscosity and density. Finally, the variations in the temperature inside the oil film were discussed to explain the shrinking phenomenon. The study provides theoretical support for the creation of oil spill clean-up methods for low-temperature waters.