350 16 Constitutive Relations
isotropic phase, whereΦμν≈Aaμνapplies, these contributions are additive. In the
nematic phase, and close to equilibrium, one hasΦμν≈0 and the relaxation term
reduces to−τa−^1 ξ 02 [Δaμν−^2 aΔ^2 aμν]. The fourth order term is proportional to the
product^2 aξ 02 , in any case.
The part of the friction pressure tensor associated with the alignment is also
modified by additional terms involving the spatial derivatives [172]. The solution of
a spatial differential equation requires boundary conditions, those appropriate for the
(16.153) and some applications are discussed in [173, 174].