Kinked Focal Conic Domains in a SmA

Abstract

International audienceWe have investigated Focal Conic Domains (FCD) in several materials that have a transition from a SmA to a nematic phase (N): the focal lines are seldom an ideal ellipse and an ideal hyperbola, and suffer large transformations (in shape and in size) when approaching the transition to the nematic phase, or appear imperfect on cooling from the nematic phase. Some examples of these transformations are shown, including the temperature dependence of the ellipse diameter. Contrari- wise, FCDs remain unchanged on heating up to or cooling down from the transition to the isotropic phase in materials that have a direct transition to the isotropic phase. We interpret the imperfections of the FCDs observed in nematogenic materials as due to the interactions of FCDs with dislocations. Such interactions are mediated through the presence of kinks on the focal lines of the FCDs, to which the dislocations are attached

Structural Rheology of the Smectic Phase

“…In the FCDs, the layers are folded into Dupin cyclides with ellipse and hyperbola which can be identified as disclinations. Kleman et al [ 47 ] and Meyer et al [ 48 ] experimentally observed that the interaction between FCDs and dislocations creates kinks on disclinations. As a result of this interaction, the screw dislocations will align along the kink.…”

“…Moreover, the dynamic coupling between the dislocation loops and the shear flow may induce the distortion of the FCDs since the dislocation loops can adapt to the applied shear stress [ 38 ]. Kleman et al [ 47 ] and Meyer et al [ 48 ] indeed pointed out that the interaction of the FCDs with dislocations causes the distortion of the FCD shape. Detailed analysis on the eccentricity would clarify how the dislocation loops attribute to the FCD structure.…”

Geometry of focal conics in sessile cholesteric droplets

“…Note that in the limit that the blue sphere center moves off to infinity along real branch, it becomes a plane tangent to the cyclide, and the cone becomes an infinite cylinder. This construction is the basis for the construction of large angle grain boundaries ( 16 ) and can also give rise to spatially varying eccentricity in thick enough freestanding films ( 20 – 23 ) or by confining a hybrid-aligned smectic with curved interfaces ( 17 ) by manipulating interface behavior with colloidal particles. Note that a sphere centered on the virtual branch at the diametrically opposed infinity also is a plane tangent to the cyclide.…”

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''.…”