Nematic twist-bend phase with nanoscale modulation of molecular orientation

TL;DR

This paper reports the discovery of a new nematic liquid crystal phase formed by achiral molecules, characterized by nanoscale oblique helicoids with a constant tilt, bridging uniaxial and chiral nematic structures.

Contribution

It experimentally demonstrates a novel twist-bend nematic phase with nanoscale modulation of molecular orientation, formed by achiral molecules, using microscopy techniques.

Findings

Identified a new nematic phase with nanoscale oblique helicoids.

Demonstrated the phase's structural relation to uniaxial and chiral nematics.

Used transmission electron and optical microscopy for characterization.

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. In this work, 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).