Can someboddy explain this from the physical point of vew?
Thank you in advance.
Hello Vladimir Farber !
Dielectric Polarization
Non-Polar Molecule
A nonpolar molecule refers to a molecule without a dipole. The charges in a nonpolar molecule are equally distributed. In spite of the lack of a dipole, a dielectric nonpolar material introduced in an electric field will be affected. In an electric field, the positive and the negative charges in a nonpolar molecule experience forces in opposite directions as a result of their opposite polarities. This force causes the electron cloud of a nonpolar molecule to be displaced in the direction of the attraction. This displacement goes on till the attraction by the electric field is balanced by the internal forces of the molecule. Thus, in the presence on an electric field, even a nonpolar molecule experiences induced dipole moment.
This dipole moment is induced in the direction of the field and is directly proportional to the strength of the electric field the nonpolar material is subject to. Both polar and nonpolar molecule experience polarization on exposure to electric field but the difference between a nonpolar and a polar molecule is that, nonpolar molecules are induced with a dipole by current whereas polar molecules have permanent dipoles. Due to the induced nature of polarity, on the removal of the electric field, a nonpolar material loses its polarity are returns to its original state.
Polar Molecule
Polar molecules undergo Dipolar Polarization which is also referred to as Orientation Polarization. A polar molecule on the other hand is already blessed with electric dipoles and this dipole is not induced. This dipole exists due to the bonds and the structure of a polar molecule. But we cannot utilize this already existing dipole moment right away. Due to thermal agitation, the dipoles in a polar material are oriented randomly. Therefore the dipole moment of the molecules in the material cancels out resulting in a net dipole moment of zero. We need to apply an electric field here as well, albeit for different purposes.
When an electric field is applied, the individual dipole moments align themselves in the direction of the electric field. This means that the bonds, their nature and their orientation remains constant and the polar molecule only rotates about its axis minutely to align itself. This alignment when summed up over all the molecules leads to a net dipole moment in the direction of the electric field. The extent to which the polar molecules get polarizes and align themselves is related to two factors; the strength of the external field and the thermal energy that breaks this alignment.
Dipolar Polarization. The already existing dipoles rotate to align with the electric field. It is also known as Orientation Polarization.
Reference: https://byjus.com/physics/dielectric-polarization-in-polar-and-nonpolar-material-and-dielectric-constant/
Dielectric anisotropy in polar solvents under external fields
Article Dielectric anisotropy in polar solvents under external fields
Structural Anisotropy in Polar Fluids Subjected to Periodic Boundary Conditions
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3269192/
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