Double-Helical Tiled Chain Structure of the Twist-Bend Liquid Crystal Phase in CB7CB
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- Univ. of Colorado, Boulder, CO (United States)
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
- Univ. of Colorado, Boulder, CO (United States); Univ. of Utah, Salt Lake City, UT (United States)
The twist-bend nematic liquid crystal phase is a three-dimensional fluid in which achiral bent molecules spontaneously form an orientationally ordered, macroscopically chiral, heliconical winding of a ten nanometer-scale pitch in the absence of positional ordering. Here, the structure of the twist-bend phase of the bent dimer CB7CB and its mixtures with 5CB is characterized, revealing a hidden invariance of the self-assembly of the twist-bend structure of CB7CB, such that over a wide range of concentrations and temperatures, the helix pitch and cone angle change as if the ground state for a pitch of the TB helix is an inextensible heliconical ribbon along the contour formed by following the local molecular long axis (the director). Remarkably, the distance along the length for a single turn of this helix is given by 2πRmol, where Rmol is the radius of bend curvature of a single all-trans CB7CB molecule. This relationship emerges from frustrated steric packing due to the bent molecular shape: space in the fluid that is hard to fill attracts the most flexible molecular subcomponents, a theme of nanosegregation that generates self-assembled, oligomer-like correlations of interlocking bent molecules in the form of a brickwork-like tiling of pairs of molecular strands into duplex double-helical chains. At higher temperatures in the twist-bend phase, the cone angle is small, the director contour is nearly along the helix axis z, and the duplex chains are sequences of biaxial elements formed by overlapping half-molecule pairs, with an approximately 45° rotation of the biaxis between each such element along the chain.
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- Institute for Complex and Adaptive Matter; National Science Foundation (NSF); USDOE Office of Science (SC), Biological and Environmental Research (BER). Biological Systems Science (BSS)
- Grant/Contract Number:
- AC02-05CH11231
- OSTI ID:
- 2446609
- Journal Information:
- Crystals, Journal Name: Crystals Journal Issue: 7 Vol. 14; ISSN 2073-4352
- Publisher:
- MDPICopyright Statement
- Country of Publication:
- United States
- Language:
- English
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