Stability of a double twisted structure in spherical cholesteric droplets

Abstract

We found for the first time the stabilization of a double twisted structure in cholesteric liquid crystals confined to small spherical droplets under weak anchoring conditions. The direct observation of the droplets using a polarized microscope revealed the physical properties of the structure. The experimental results showed that the stability of the double twisted structure is determined by the relationship between the helical pitch length and the droplet size. We theoretically analyzed the structural stability by the calculation of the Frank elastic free energy including the surface elastic term, and succeeded in explaining the experimental results. In this paper, we concluded that the stability of the double twisted structure is determined by the competition between the surface and the bulk elasticity.

Topological Formations in Chiral Nematic Droplets

“…A specific property of droplets compared to other confined systems is their symmetry -a structure can be embedded in a spherical confinement in any orientation, giving rise to several possible different appearances of the same structure. Caution is even more critical in cholesteric droplets, where often several metastable states are possible and the nontrivial optics of the system hinders interpretation of optical textures [6,[94][95][96][97][98].…”

Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions

“…As a result, the dependence of the forming structure on the droplet size (in our case, the number N of the layer-like structure) should be more complicated compared to the case of strong anchoring. A formation of the layer-like structure leads to either a local disturbance of the boundary conditions, as in the case of weak surface anchoring [45] or an appearance of the linear surface defect as in the case of strong homeotropic anchoring [38]. The double twisted defect loop is formed near the droplets surface under study (Figures 4 and 5).…”

“…In this case, the position of the intervals' boundaries ( Figure 5e) should be dependent on the anchoring energy value and/or the intrinsic helix pitch p 0 . For instance, in the work of Yoshioka et al [45], the transition between an axisymmetric double twisted structure (C ∞ ) and a layer-like structure occurs at N 0 ∼ = 2.1 without the formation of intermediate structures.…”

“…It is known that a weak conical anchoring appears at the interface of LC and own isotropic phase. In this case, the axisymmetric (C ∞ ) double twisted structure (N 0 < 2) or the defect-free structure with the uniform helix axis distribution (N 0 > 2) have been observed in cholesteric droplets [43][44][45][46]. Recently, we have obtained and investigated the nematic droplets dispersed in polymer with the conical boundary conditions [47].…”

Spherical-cap droplets of a photo-responsive bent liquid crystal dimer

“…Cholesteric (Ch), smectic (Sm), or columnar (Col) LC systems with curved boundaries are more complicated [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], because the director structures are dominated not only by the two factors described already but also by others, such as helix formation due to the chirality or the compression elasticity due to the translational ordering with molecular length scales. The key point to be noticed here is the role played by frustration among these factors.…”