Journal of Colloid and Interface Science, Vol.586, 257-268, 2021
Coalescence and spreading of drops on liquid pools
Hypothesis: Oil spills have posed a serious threat to our marine and ecological environment in recent times. Containment of spills proliferating via small drops merging with oceans/seas is especially difficult since their mitigation is closely linked to the coalescence dependent spreading. This inter-connectivity and its dependence on the physical properties of the drop has not been explored until now. Furthermore, pinch-off behavior and scaling laws for such three-phase systems have not been reported. Experiments: We investigate the problem of gentle deposition of a single drop of oil on a pool of water, representative of an oil spill scenario. Methodical study of 11 different n-alkanes, polymers and hydrocarbons with varying viscosity and initial spreading coefficients is conducted. Regime map, scaling laws for deformation features and spreading behavior are established. Findings: The existence of a previously undocumented regime of delayed coalescence is reported. A novel application of the inertia-visco-capillary (I-V-C) scale collapses all experimental coalescence data on a single line while the early stage spreading is found to be either oscillatory or asymptotically reaching a constant value, depending on the viscosity of the oil drop unlike the well documented monotonic, power law late-time spreading behavior. These findings are equally applicable to applications like emulsions and enhanced oil recovery. (C) 2020 Elsevier Inc. All rights reserved.