Imperfections in focal conic domains: the role of dislocations

Abstract

It is usual to think of Focal Conic Domains (FCD) as perfect geometric constructions in which the layers are folded into Dupin cyclides, about an ellipse and a hyperbola that are conjugate. This ideal picture is often far from reality. We have investigated in detail the FCDs in several materials which have a transition from a smectic A (SmA) to a nematic phase. The ellipse and the hyperbola are seldom perfect, and the FCD textures also suffer large transformations (in shape or/and in nature) when approaching the transition to the nematic phase, or appear imperfect on cooling from the nematic phase. We interpret these imperfections as due to the interaction of FCDs with dislocations. We analyze theoretically the general principles subtending the interaction mechanisms between FCDs and finite Burgers vector dislocations, namely the formation of kinks on disclinations, to which dislocations are attached, and we present models relating to some experimental results. Whereas the principles of the interactions are very general, their realizations can differ widely in function of the boundary conditions.Comment: 19 pages, 18 figure

How Do Defects Transform at the Smectic A-Nematic Phase Transition?

“…We will give more details on the mechanisms of the FCD modifications in a forthcoming publication [12]; these mechanisms are also visible in the case of homeotropic samples. Let us conclude by a final remark relating to another type of FCD-dislocations interaction.…”

Kinked Focal Conic Domains in a SmA

“…How does an imperfect FCD look? Recently [3,4] we have demonstrated that an imperfect FCD is a Kinked FCD. A kink plays a role of the imperfection on a disclination.…”

Double helical defects in smectic A and smectic A* phases

“…Imperfections in the ideality of FCDs have been recently investigated [9][10][11]; some of these are macroscopic, but most are microscopic, described as ''kinks''.…”