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For example, consider a pot of water with a drop of oil floating on it, with surfactants present in the water.

Will the surfactants in the water spread evenly across all three interfaces (water/metal, water/air, and water/oil)?

Are there material-specific surfactants, such that each of the three interfaces might attract different surfactants?

If so, are there also surfactants that would tend to spread across all three interfaces evenly?

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A surfactant is a material that has two regions, one that tends to be attracted to its environment, and another that is repelled by the environment. The amount to which they will be attracted to one interface or another depends upon whatever would minimize the total free energy of the system. Thus, unless the interactions for water/oil, water/air, and water/surface were equivalent, you should see that the surfactant preferentially moves to the interface where it will have the biggest impact on the free energy.

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