http://orcid.org/0000-0002-3826-8024
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Abstract
Spreading of liquids on solid surfaces is an important process from both fundamental and applied viewpoints. Over the past few decades, many interests have focused on the spreading behavior and spreading mechanism of pure liquids and/or surfactant solutions over different hydrophobic substrates in air, however, there are a few studies to investigate the spreading behavior of oily liquids on solid surfaces in aqueous environment. Therefore, this paper aimed to study the spreading behavior of oil (oleic acid) droplets on a highly hydrophobic substrate, Polytetrafluoroethylene (PTFE), in deionized water. Experiments were conducted using a manufactured device based on high-speed microscopic imaging technology, and the spreading kinetics was characterized in terms of dynamic contact angle, spreading radius and spreading height. Results showed that the ‘approach-bounce’ behavior of oil droplets over solid in deionized water was similar to that of bubbles in water. The whole spreading process could be separated into two stages: the initial fast inertial spreading stage and the subsequent slow viscous spreading stage. In the inertial force dominated stage, the spreading radius increased rapidly in a scaling law of R ∼ t 0.5, while it increased slowly with t 0.1 during the viscous force dominated stage. In addition, the dynamic contact angle and spreading height also exhibited similar behavior. These findings can provide the guidance for the separation industries such as adsorption of oily agents on mineral surfaces to increase physicochemical differences between different components in flotation, and recovery of crude oil from oil wells.
Graphical Abstract
