CORE STRUCTURE OF A SCREW DISCLINATION IN SMECTIC-A LIQUID-CRYSTALS

The core structure of a sorew dislocation in the smectic-A matrix is s tudied using the covariant form of the Landau-de Gennes free-energy de nsity. Three qualitatively different core structures are found. In sol ution (i) the screw dislocation is singular only in the smectic compon ent, while in solution (ii) the defect is also present in the nematic director field. In solution (iii) smectic layers bend significantly ou t of the undistorted reference plane and the core is singular in both components. In addition, it is shown that, if the smectic phase is com posed of a mixture of conformers with opposing twist sense, the screw dislocation can cause spatial variation of individual mixture componen t concentrations. This can in turn influence the core structure itself .