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Wetting-nonwetting transition at the liquid-air interface of methanol-cyclohexane-water mixtures.

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Kahlweit,  M.
Abteilung Kinetik der Phasenbildung, MPI for biophysical chemistry, Max Planck Society;

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Busse,  G.
Abteilung Kinetik der Phasenbildung, MPI for biophysical chemistry, Max Planck Society;

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Haase,  D.
Abteilung Kinetik der Phasenbildung, MPI for biophysical chemistry, Max Planck Society;

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Citation

Kahlweit, M., Busse, G., Haase, D., & Jen, J. (1988). Wetting-nonwetting transition at the liquid-air interface of methanol-cyclohexane-water mixtures. Physical Review A, 38(3), 1395-1401. doi:10.1103/PhysRevA.38.1395.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002D-4D1F-A
Abstract
In mixtures of methanol and cyclohexane, a layer of the lower methanol-rich phase (a) intrudes between the upper cyclohexane-rich phase (b) and air (c). As water is added, the layer disappears. In the literature, this effect is interpreted as a wetting-nonwetting transition near a critical point. We suggest instead considering the transition as being caused by the effect of water on the surface tensions σac and σbc of the two liquid phases against air: In the water-free mixture one finds wσ≡(σbc-σac)/σab>1. Consequently, the b/c interface is thermodynamically unstable, and the system minimizes its free energy by placing a layer of phase a between phase b and air. As water is added, both σac and σab increase steeply, whereas σbc is less affected, which makes wσ decrease. As soon as wσ<1, the b/c interface becomes stable and the system gradually disposes with the layer of phase a.