  Several oil-water separation techniques have been proposed to improve the
capacity of cleaning water. With the technological possibility of producing
materials with antagonist wetting behavior, as for example a substrate that
repeal water and absorb oil, the understanding of the properties that control
this selective capacity has increased with the goal of being used as mechanism
to separate mixed liquids. Besides the experimental advance in this field, less
is known from the theoretical side. In this work we propose a theoretical model
to predict the wetting properties of a given substrate and introduce
simulations with a 4-spins cellular Potts model to study its efficiency in
separating water from oil. Our results show that the efficiency of the
substrates depends both on the interaction between the liquids and on the
wetting behavior of the substrates itself. The water behavior of the droplet
composed of both liquids is roughly controlled by the hidrophobicity of the
substrate. To predict the oil behavior, however, is more complex because the
substrate being oleophilic do not guarantee that the total amount of oil
present on the droplet will be absorbed by the substrate. For both types of
substrates considered is this work, pillared and porous with a reservoir, there
is always an amount of reminiscent oil on the droplet which is not absorbed by
the substrate due to the interaction with the water and the gas. Both
theoretical and numerical models can be easily modified to analyse other types
of substrates and liquids.
