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Effect of strong confinement on defect structures of cholesteric blue phases
Jun-ichi Fukuda1,2 and Slobodan Zumer2,3
1 Nanosystem Research Institute, AIST, 1-1-1 Umezono, Tsukuba 305-8568, Japan
2 Department of Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
3 Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

Cholesteric blue phases (BPs) [1] found in highly chiral liquid crystals are interesting examples of three-dimensional ordered structures in soft materials. They appear as a result of frustrations between local preference of a double-twist configuration over a single twist, and a global topological constraint that a double-twist configuration cannot fill the whole space. Though the structures of bulk BPs with cubic symmetry are now well established, it is not yet understood how the anchoring of confining surfaces affects the order of structures of BPs. Here we discuss the structures of topological defects in a strongly confined chiral liquid crystal [2].
Our study is based on numerical calculations using a Landau–de Gennes theory, in which the orientational order is described by a second-rank tensor. Defect structures in a planar cell imposing homeotropic anchoring at the surfaces do not resemble those of bulk BPs and can indeed be thermodynamically stable when the cell thickness is of the order of the dimension of the unit cell of bulk BPs. These novel defect structures can be regarded as a consequence of a different frustration between the local preferred structure of a regular array of disclinations, and the constraint imposed by the anchoring of confining surfaces. Our results indicate that there are still possibilities for unknown ordered structures in liquid crystals arising from more complex frustrations.
We acknowledge financial support by Slovenian Research Agency (ARRS research program P1- 0099 and project J1-2335) and KAKENHI (Grant-in-Aid for Scientific Research) on Priority Area “Soft Matter Physics” from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

[1] D.C. Wright and N.D. Mermin, Rev. Mod. Phys. 61, 385 (1989).
[2] J. Fukuda and S. Zumer, Phys. Rev. Lett. 104, 017801 (2010); Liq. Cryst. (to be published).

"Jožef Stefan" Institute

University of Ljubljana
Faculty of Mathematics
and Physics

Center of Excellence