Biaxial, Twist-bend, and Splay-bend Nematic Phases of Banana-shaped Particles Revealed by Lifting the “Smectic Blanket”

Abstract

We perform an extensive computational study on the phase behavior of hard banana-shaped particles, and show that biaxial, twist-bend, and splay-bend nematic phases are metastable with respect to a smectic phase for a system of hard bent spherocylinders. However, if the smectic phase is destabilized-either by polydispersity in the particle length or by curvature in the particle shape-stable biaxial, twist-bend, and splay-bend nematic phases are obtained. This provides a unified and consistent picture on the subtle role of particle shape on the phase behavior of bent rods.

Shaping colloidal bananas to reveal biaxial, splay-bend nematic, and smectic phases

“…The vast majority of these are smectic (Sm) phases, as the curved shape of the constituting molecules promotes their locking into smectic layers (8,9). The large stability of Sm phases has also been observed in experiments of colloidal 'boomerang-like' particles (16), and in computer simulations of similarly shaped particles (17). The rather uncommon observation of nematic phases in bananashaped systems (18,19) has been of interest for the past 20 years, not least because of their potential to form chiral and biaxial nematic phases (13,17,20,21).…”

Molecular Flexibility and Bend in Semi‐Rigid Liquid Crystals: Implications for the Heliconical Nematic Ground State

“…In reality, the relationship between the scaled transition temperature and either the FWHM or average bend angle cannot be taken in isolation. A favourable FWHM and unfavourable bend angle (or vice versa) would not be expected to generate the N TB phase: consider the large number of rigid bent‐core liquid crystals which do not exhibit twist‐bend nematic phases, although these may be hidden by the “smectic blanket” . In this work, the materials studied feature a methylene spacer with varying linking group; it is therefore to be expected that as linkers are used which introduce greater flexibility (increased FWHM) the average bend angle decreases further away from the tetrahedral angle imposed by the methylene spacer.…”

Helicoidal dynamics of biaxial curved rods in twist-bend nematic phases unveiled by unsupervised machine learning techniques

“…Our newly devised DMC method to simulate Brownian particles with a nontrivial roto-translational coupling and the dimensionality reduction method to project particle trajectories onto a low-dimensional manifold can be generalized to study the dynamics of arbitrarily shaped particles on various manifolds, e.g. the long-time diffusion in splay-bend nematics [18]. Furthermore, our study provides an insight into the macroscopic transport properties and reveals a link between the structural and dynamical properties in N T B phases, which are both relevant for applications that rely on the type and speed of the macroscopic diffusion, e.g.…”

“…Due to the ease to manipulate this director with electric fields, nematic liquid crystals have revolutionized the way we display information with devices ranging from organic LEDs to LCDs in smart phones, laptop screens, and flatpanel TVs [1][2][3][4][5]. Very recently, a fascinating chiral nematic phase has been discovered in which the orientation of achiral banana-shaped bent-core mesogens twists and bends at a very small length scale [6][7][8][9][10][11][12][13][14][15][16][17][18]. This twist-bend nematic (N T B ) phase is characterised by an oblique heliconical winding of the nematic director field n(z) = sin(θ 0 ) cos(qz)ê x +sin(θ 0 ) sin(qz)ê y +cos(θ 0 )ê z , with q = 2π/p the wave number of the heliconical twist, θ 0 the conical angle, and p the pitch length (see FIG.…”

“…Despite numerous efforts, simulations that succeeded to stabilize an N T B phase are scarce [21][22][23]. We recently discovered that an N T B phase can be stabilized in systems of curved hard rods [18]. In this Letter, we use this model to study the long-time translational diffusion in N T B phases of various handedness, pitch, and conical angle, and compare it with the macroscopic transport properties of isotropic and nematic phases.…”