Distortional polarisability

Molecular polarisability is the result of two mechanisms (a) distortional polarisation and (b) orientation polarisation. Distortional polarisation is the result of the change of electric charge distribution in a molecule due to an applied electric field, thereby inducing an electric dipole. This distortional polarisation is coined ad. Permanent dipoles are also present in the absence of an electric field. At the application of an electric field they will orient more or less in the direction of the electric field, resulting in orientation polarisation. However, the permanent dipoles will not completely align with the electric field due to thermal agitation. It appears that the contribution of molecular polarisability from rotation is approximately equal to p2/(3kT). Accordingly, the total molecular polarisability is... 

When ions with this structure diffuse to the vicinity of a negative cathode, the ion is distorted by the field to become polarised, with the positive silver core nearest the cathode (see Fig. 12.2). Once within a critical distance the... 

Some investigatorshave advocated a type of accelerated test in which the specimens are coupled in turn to a noble metal such as platinum in the corrosive environment and the currents generated in these galvanic couples are used as a measure of the relative corrosion resistance of the metals studied. This method has the defects of other electrolytic means of stimulating anodic corrosion, and, in addition, there is a further distortion of the normal corrosion reactions and processes by reason of the differences between the cathodic polarisation characteristics of the noble metal used as an artificial cathode and those of the cathodic surfaces of the metal in question when it is corroding normally. 

Fig. 6. The two generic shapes of molecules which exhibit flexoelectric polarisation under distortion of the equilibrium director distribution...

If the cation is small and has a high charge, i.e. it has a high charge density, it is very polarising. Such a cation will distort the electron cloud of the anion, pulling the electron density towards itself. 

Ionic Polarisability Polarisability of an atom is the ability of the applied electric field to distort the electric cloud and thus induce an electric dipole moment. 

---