Phenomenological model of a polar liquid (see also our publications) predicts ferro-electric ordering and 3D ferroelectric phase transition as a reason behind lambda-transition in supercooled water. According to our analytical estimations it occurs at T=210-240K, which coincides nicely with the actually observed temperature range (about 228K). A similar 2D phase transition in a polar liquid in a thin ferro-electric layer of water molecules formed on a hydrophobic interface occurs at a strictly large temperature > 228K, the exact value of which depends on the hydrophobic properties of the surface.

The true picture of the water molecules ordering next to a hydrophobic surface or a liquid-gas interface is in fact more complicated than a model. Next to the interface both the water polarization and the density should vanish. To account for the density changes we incorporated the density variations into the free energy functional. The resulting model even though only in the mean field approximation reveals spontaneous liquid polarization at the liquid boundary. To see that we solved the mean field equations and plotted both the liquid density and the average dipole moment (along the water surface) next to the liquid boundary.

The spontaneous polarization of the liquid is the consequence of the dipole-dipole interactions and effectively makes the liquid interface behave as a ferro-electric film. The true value of the net dipole moment of the water surface depends on the liquid properties and is subject to fluctuations. At the end, since the dipole moment is essentially 2D the fluctuations can destroy the ferro-electric ordering in a phase transition similar to BKT.

The validity of the mean field picture represented above depends on the density of the liquid: . In realistic situations the parameter is not very large and this may inhibit observations of the order parameter in molecular dynamics situations.

Related posts:

1. Molecular polarization on a polar liquid interface: the structure of a water surface
2. Ferro-electric phase transition in a polar liquid and the nature of lambda-transition in supercooled water
3. Ferro-electric phase transition in a polar liquid and the nature of \lambda-transition in supercooled water
4. Spontaneous polarization of a polar liquid next to nano-scale impurities
5. Water molecules alignments on a hydrophobic surface – I