Topological defects in schlieren textures of biaxial and uniaxial nematics

Abstract

Monte Carlo and theoretical studies of thin 3D films of biaxial and uniaxial nematics with tangential boundary conditions show distinct differences in structure and evolution of topological defects. In the uniaxial films, defects of strength k=+/-1 are point defects that bear no bulk singularity and disappear by annihilation with each other. In the biaxial films, k=+/-1 defects are true singular bulk disclinations that split into pairs of k=+/-1/2 lines; the latter disappear by annihilation processes of the type +1/2-1/2=0. These observed differences are of relevance for the current debate on the existence of biaxial phases.

Biaxial Nematic Droplets and their Optical Textures: A Lattice Model Computer Simulation Study

“…Experiments by Chandrasekhar et. al [7] and, more recently, investigations on lyotropic [8] and thermotropic [4,5,9] systems seem to support this hypothesis which we have also verified by computer simulations of a schlieren texture, at least in some biaxial nematic films [10]. The problem of the molecular organization and of the optical texture of biaxial nematics in spherical droplets is also of interest in view of the expected differences in topological defect structure [11].…”

“…While in simulating bulk systems [13,14] and toroidal boundary conditions [16] and thin films with hybrid [17] and schlieren anchoring geometries [10]. Here we present an investigation of biaxial nematic droplets with various selected boundary conditions.…”

Computer Simulations of Biaxial Nematics

“…The experimental identification of biaxiality has always proved to be fairly difficult [16,42,43], and still does because of the small magnitude of the transversal orientational ordering, and the necessity of filtering out the possible perturbations arising from laboratory setup, and anchoring conditions [43]. Actually, this is an additional hurdle to cope with for those scientists trying to characterise potentially N b systems.…”

Some Features of Liquid Crystalline Oxadiazoles

“…Numerical simulations [6] of transitions, from the ordinary nematic to the biaxial one, give the evolution of schlieren textures as they can be observed with the polarized light microscope. It results that the problem is more complex than what is commonly suggested, that it is the charge of disclinations which distinguishes the biaxial form from the uniaxial phase.…”