2.4 The Static Dielectric Constant
73
• The concept that a group of five molecules can orient as a unit while retaining an
internal freedom of rotation seems incompatible with the notion of an extended
tetrahedral network structure [11].
• Using (2.50), the dielectric constant does not reduce to ∞ at frequencies sufficiently high for the contribution of the permanent dipole, μ 0 , orientation to become
zero, as expected for scalar isotropic polarizability [10].
• The Debye–Onsager–Kirkwood–Fröhlich theory of the dielectric polarization
assumes a dramatic stretching of the water molecule in the liquid state in comparison with the gas phase, which is not confirmed by IR and neutron scattering
measurements. For example, an adequate description of the experimental curve
is possible (see Fig. 1.27) with the dipole moment μ = 3.32 D, which is 180%
larger than the gas-phase dipole moment μ 0 = 1.85 D. However, the comparison of
the data from the neutron diffraction of ice [34] and the IR spectroscopy of water
vapor [35] shows that the O–H distance changes from 0.099 and 0.096 nm, respectively, showing a less than 4% difference. Furthermore, the IR molecular stretching
modes shift from gas to liquid only a few percent toward lower frequencies (see
Sect. 2.5).
• There is no uniform model for ice and water. The experimental temperature dependence of the static dielectric constant is achieved with different structural parameters for ice and water [36], while they are very similar from the IR spectroscopy
point of view (see Sect. 2.5).
• The static dielectric constant is 95% formed by the dielectric relaxation band (see
Sect. 2.3). The self-diffusion coefficients of water and ice are so high (see Sect. 1.4)
that during the relaxation time each particle is displaced by several molecular
distances, and thus they are oriented and translated many times. In other words,
any molecular configurations are destroyed by thermal shuffling over the period
of the external field. Diffusion should lead to the averaging of all intermolecular
dipole moments.
• In a system of identical dipole moments, individual dipoles tend to lose their identity and “dissolve” in a system of compensating polar charges. The compensation
occurs by a change in the electrostatic free energy of the system; therefore, polar
liquids with a high Onsager’s local-field ordering are expected to be poor solvents,
which is not the case for water.
Thus, the Debye–Onsager–Kirkwod–Fröhloch’s mechanism of “dipole moment
self-induction,” which is based on the Bernal–Fowler water model, assumes that
the reference H 2 O molecule is immersed in a medium of much smaller polarizable
particles. However, in Bernal–Fowler water, molecules are all the same size, and the
closing fields required by Onsager’s theory cannot be built with identical dipoles [11].
The problem of Onsager’s approach originates from the inappropriate mixing of
macroscopic and microscopic concepts. The theory of the local field fails, because
it does not account for intermolecular polarization effects, dealing with molecular
dipoles only.
73
• The concept that a group of five molecules can orient as a unit while retaining an
internal freedom of rotation seems incompatible with the notion of an extended
tetrahedral network structure [11].
• Using (2.50), the dielectric constant does not reduce to ∞ at frequencies sufficiently high for the contribution of the permanent dipole, μ 0 , orientation to become
zero, as expected for scalar isotropic polarizability [10].
• The Debye–Onsager–Kirkwood–Fröhlich theory of the dielectric polarization
assumes a dramatic stretching of the water molecule in the liquid state in comparison with the gas phase, which is not confirmed by IR and neutron scattering
measurements. For example, an adequate description of the experimental curve
is possible (see Fig. 1.27) with the dipole moment μ = 3.32 D, which is 180%
larger than the gas-phase dipole moment μ 0 = 1.85 D. However, the comparison of
the data from the neutron diffraction of ice [34] and the IR spectroscopy of water
vapor [35] shows that the O–H distance changes from 0.099 and 0.096 nm, respectively, showing a less than 4% difference. Furthermore, the IR molecular stretching
modes shift from gas to liquid only a few percent toward lower frequencies (see
Sect. 2.5).
• There is no uniform model for ice and water. The experimental temperature dependence of the static dielectric constant is achieved with different structural parameters for ice and water [36], while they are very similar from the IR spectroscopy
point of view (see Sect. 2.5).
• The static dielectric constant is 95% formed by the dielectric relaxation band (see
Sect. 2.3). The self-diffusion coefficients of water and ice are so high (see Sect. 1.4)
that during the relaxation time each particle is displaced by several molecular
distances, and thus they are oriented and translated many times. In other words,
any molecular configurations are destroyed by thermal shuffling over the period
of the external field. Diffusion should lead to the averaging of all intermolecular
dipole moments.
• In a system of identical dipole moments, individual dipoles tend to lose their identity and “dissolve” in a system of compensating polar charges. The compensation
occurs by a change in the electrostatic free energy of the system; therefore, polar
liquids with a high Onsager’s local-field ordering are expected to be poor solvents,
which is not the case for water.
Thus, the Debye–Onsager–Kirkwod–Fröhloch’s mechanism of “dipole moment
self-induction,” which is based on the Bernal–Fowler water model, assumes that
the reference H 2 O molecule is immersed in a medium of much smaller polarizable
particles. However, in Bernal–Fowler water, molecules are all the same size, and the
closing fields required by Onsager’s theory cannot be built with identical dipoles [11].
The problem of Onsager’s approach originates from the inappropriate mixing of
macroscopic and microscopic concepts. The theory of the local field fails, because
it does not account for intermolecular polarization effects, dealing with molecular
dipoles only.