In the case of an isotropic material both surface tension and diffusivity are independent of the crystalline orientation and are given by and , say. This evolution equation becomes
where
Tritscher (1996a) showed that (7) was also an integrable form of the governing equation (5) for a class of anisotropic materials with behaviour similar to a liquid crystal and constitutive relations
where
By use of symmetry recursion operators applied to the linearizable nonlinear diffusion equation Broadbridge & Tritscher (1996) derived a further linearizable form of the evolution equation
where
The constitutive functions show degeneracy and for values of |