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Effect of Model Polycyclic Aromatic Compounds on the Coalescence of Water-in-Oil Emulsion Droplets

Jian, Cuiying, Liu, Qingxia, Zeng, Hongbo, Tang, Tian
The Journal of Physical Chemistry C 2017 v.121 no.19 pp. 10382-10391
adsorption, droplets, emulsions, heptane, kinetics, molecular dynamics, oils, polycyclic compounds, simulation models, solvents, toluene
A series of molecular dynamics simulations were performed to investigate the effect of polycyclic aromatic compounds (PACs) on the coalescence of two water droplets in oil (i.e., n-heptane and toluene). Our simulations revealed that, in both solvents, the presence of PACs can significantly hinder the coalescence or even completely prevent it. Detailed structural and kinetic analysis provided insights into the underlying mechanisms for the coalescence inhibition. In n-heptane, regardless of their concentration, the PAC molecules formed an adsorption layer on the water droplets which, if the concentration is sufficiently high, is able to introduce strong steric hindrance and shield the water–water interaction. While the formation of an adsorption layer was also observed in toluene at sufficiently high PAC concentration, the prevention of coalescence at relatively low concentration is mainly driven by the unadsorbed, free-floating PAC molecules in the bulk toluene. The simulation results reported here fully agree with our previous experimental observations and well interpreted the experimental results from the atomic level.