ROTATIONAL DIFFUSION OF UNIAXIAL PROBES IN BIAXIAL LIQUID-CRYSTAL PHASES

We discuss the reorientation of a cylindrically symmetric probe in a b iaxial orthorombic medium, such as a biaxial nematic. We write down an d solve for the first time the rotational diffusion equation for a rod -like or disc-like uniaxial probe reorienting in a medium of biaxial s ymmetry. We calculate first and second rank correlation functions both in the uniaxial and biaxial phase, giving the possibility of followin g the evolution of dynamic observables of interest (e.g. spectral dens ities) through the uniaxial-biaxial phase transition. Nonperturbative and approximate analytical solutions are provided.