Letter

Nature 437, 525-528 (22 September 2005) | doi:10.1038/nature04034; Received 24 April 2005; Accepted 30 June 2005

Optical isotropy and iridescence in a smectic 'blue phase'

Jun Yamamoto1,2,3, Isa Nishiyama1, Miyoshi Inoue1 & Hiroshi Yokoyama1,2

  1. ERATO Yokoyama Nano-structured Liquid Crystal Project, JST, 5-9-9 Tokodai, Tsukuba 300-2635, Japan
  2. Nanotechnology Research Institute, AIST, 1-1-1 Umezono, Tsukuba 305-8568, Japan
  3. †Present address: Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-8502, Japan

Correspondence to: Jun Yamamoto1,2,3 Correspondence and requests for materials should be addressed to J.Y. (Email: jun@junyamamoto.jp).

When liquid crystal molecules are chiral, the twisted structure competes with spatially uniform liquid crystalline orders, resulting in a variety of modulated liquid crystal phases, such as the cholesteric blue phase1, twist grain boundary2, 3, 4 and smectic blue phases5. Here we report a liquid crystal smectic blue phase (SmBPiso), formed from a two-component mixture containing a chiral monomer and a 'twin' containing two repeat units of the first molecule connected by a linear hydrocarbon spacer. The phase exhibits the simultaneous presence of finite local-order parameters of helices and smectic layers, without any discontinuity on a mesoscopic length scale. The anomalous softening of elasticity due to a strong reduction in entropy caused by mixing the monomer and the twin permits the seamless coexistence of these two competing liquid crystal orders. The new phase spontaneously exhibits an optically isotropic but uniformly iridescent colour and automatically acquires spherical symmetry, so that the associated photonic band gap6, 7, 8, 9 maintains the same symmetry despite the local liquid crystalline order. We expect a range of unusual optical transmission properties based on this three-dimensional isotropic structure, and complete tunability due to the intrinsic softness and responsiveness of the liquid crystalline order against external fields.

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