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Chapter V Dielectric Study of ……
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orientation of the molecules of a polar dielectric having a constant dipole
moment in the direction of an electric field. In the original theory, the model of
an orienting polar molecule was a sphere rotating in a viscous medium and
overcoming a friction. If orientational polarization is considered more strictly it
must be understood as the introduction by an electric field of certain
orderliness in the position of polar molecules being in uninterrupted chaotic
thermal motion and not as a direct rotation of polar molecules under the action
of an electric field. For this reason, orientational polarization is connected by
its nature with the thermal motion of molecules and temperature must exert an
appreciable effect on the phenomenon of orientational polarization.
Orientational polarization can appear in a pure form only in gases,
liquids and amorphous viscous bodies. In crystals at a temperature below the
melting point the dipoles are said to be "frozen", i.e., secured in their places
so tightly that they can not be oriented and hence the orientational
polarization can not occur in them. The orientational polarization sometimes,
manifests itself in some crystals with loose packing of molecules, for example,
water ice. In some cases for example in cellulose and its derivatives there
may be rotations of not complete molecules but of their separate parts.
After a dielectric is energized or de-energized, the process of establishing
a orientational polarization requires a relatively long time as compared with
that of deformated orientational polarization.
This type of polarization occurs in liquids or gases when molecules
having a permanent or induced dipole moment aligned along the applied field.
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