Nematic twist-bend phase with nanoscale modulation of molecular orientation.
Nat Commun 2014;
4:2635. [PMID:
24189583 PMCID:
PMC3831290 DOI:
10.1038/ncomms3635]
[Citation(s) in RCA: 283] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 09/18/2013] [Indexed: 11/12/2022] Open
Abstract
A state of matter in which molecules show a long-range orientational order and no positional order is called a nematic liquid crystal. The best known and most widely used (for example, in modern displays) is the uniaxial nematic, with the rod-like molecules aligned along a single axis, called the director. When the molecules are chiral, the director twists in space, drawing a right-angle helicoid and remaining perpendicular to the helix axis; the structure is called a chiral nematic. Here using transmission electron and optical microscopy, we experimentally demonstrate a new nematic order, formed by achiral molecules, in which the director follows an oblique helicoid, maintaining a constant oblique angle with the helix axis and experiencing twist and bend. The oblique helicoids have a nanoscale pitch. The new twist-bend nematic represents a structural link between the uniaxial nematic (no tilt) and a chiral nematic (helicoids with right-angle tilt).
Theories predict the existence of a nematic liquid crystal phase with a local twist-bend structure, but no experimental proof is available over the past 40 years. Borshch et al. identify this phase for the first time in two different materials containing dimeric molecules.
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