Liquid Crystals. Iam-Choon Khoo
href="#fb3_img_img_66981a42-c73d-5b41-95bb-1d06c7b10637.png" alt="ModifyingAbove upper M With right harpoon with barb up"/>, the magnetic induction
(3.20)
and
(3.21)
The magnetic susceptibility tensor
(3.22)
Note that this is similar to the dielectric constant
Nematic liquid crystals, in fact, liquid crystals in general, are diamagnetic. Therefore,
3.3.2. Free Energy and Torques by Electric and Magnetic Fields
In this section, we consider the interactions of nematic liquid crystals with applied fields (electric or magnetic); we will limit our discussion to only dielectric and diamagnetic interactions.
For a generally applied (dc, low frequency, or optical) electric field
(3.23)
The electric interaction energy density is therefore
Note that the first term on the right‐hand side of Eq. (3.24) is independent of the orientation of the director axis. It can therefore be neglected in the director axis deformation energy. Accordingly, the free‐energy density term associated with the application of an electric field is given by
(3.25)
in SI units (in cgs units,
Similar considerations for the magnetic field yield a magnetic energy density term Um given by
(3.27)
a magnetic free‐energy density (associated with director axis reorientation) Fm given by
(3.28)
and a magnetic torque density