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Abstract
In this paper, a hydroxylated graphite surface is generated as a hydrophilic oleophobic material for the application of oil-water separation, and the effects of hydroxyl density on the three-phase wettability are studied in oil-water-graphite systems. We analyze the adsorption of water molecules on the hydroxylated surfaces and obtain the relationship between water-oil-solid interfacial properties and the hydroxyl density, which results from the synthetic effects of the orientation of molecules and hydrogen bonds. With the increase of hydroxyl density, the water-solid contact angle first decreases rapidly, and then remains constant. The density of the hydrogen bond formed between hydroxyls and water molecules in the adsorption layer can explain the regularity of the three-phase wettability. The orientation of the water molecules in the adsorption layer shows insignificant variation, owing to the hydrogen bond network formed between the water molecules; thus, little change is observed in the hydrogen bond density in the adsorption layer.
Highlights
The water content of crude oil increases during oil recovery due to water injection, leading to increases attention to the study of oil-water separation [1]
We focus on generating a hydroxylated graphite surface, and reveal the mechanism of the effect of hydroxyls on the wettability of graphite surfaces in a three-phase system using the Molecular Dynamics (MD) simulation
We find that theincreases number with the increase in hydroxyl density, which a different from that with the contact angle
Summary
The water content of crude oil increases during oil recovery due to water injection, leading to increases attention to the study of oil-water separation [1]. The main idea is to prepare a hydrophilic oleophobic surface in a water environment [6] For this process, the wettability problem [7] in the oil-water-solid three-phase system needs to be studied. Graphite is a typical example of a carbon material that has many advantages, such as high stability, corrosion resistance to acid/alkali and organic solvents, and the ability to withstand severe changes of temperature [13,14] It is often used as the hydrophobic oleophilic material for the oil-water separation. With the increase of hydroxyl density, the effects of hydroxyls on the orientation of water molecules and the density of hydrogen bonds in the adsorption layer may be different, contributing significantly to the surface wettability.
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