Wojciech Tomczyk

In the study by Birdi et al. molecular dynamics simulations were employed to investigate the coarsening dynamics of bent-core liquid crystals with a focus on the phase transition from a polar smectic X phase to the chiral twist-bend phase. A key finding is the emergence of an intermediate splay-bend phase before the system reaches the stable twist-bend phase. In this comment, we rectify the erroneous assumption that led to the improper conclusions and elucidate that the intermediate system studied by Birdi et al. is either a disordered smectic X (banana phase B1) or splay-bend smectic.

Mesogenic properties arise from the right conditions imposed by the molecular structure of molecules. Knowledge of how, for example, alterations in molecules length-to-width ratio affect mesophase emergence is of crucial importance. Motivated by ongoing research on the nature of the twist-bend nematic phase and its structural characteristics, we conducted Monte Carlo simulations of bent-shaped molecules represented as a rigid set of n hard tangent spheres evenly attached along the arc. With a fixed bend angle, we have identified a set of mesophases in the domain of variable n and packing fraction η, among which are twist-bend nematic, splay-bend smectic, and type 1 columnar banana phase─for the first time being reported in a computational study.

A generalized Landau-de Gennes theory is proposed that comprehensively explains currently available experimental data for the heliconical twist-bend nematic (N_TB) phase observed in liquid crystalline systems of chemically achiral bent-core-like molecules. A bifurcation analysis gives insight into possible structures that the model can predict and guides in the numerical analysis of relative stability of the isotropic (I), uniaxial nematic (N_U) and twist-bend nematic phases. An estimate of constitutive parameters of the model from temperature variation of the nematic order parameter and the Frank elastic constants in the nematic phase enables to demonstrate quantitative agreement between the calculated and experimentally determined temperature dependence of the pitch and conical angle in N_TB. Properties of order parameters also explain a puzzling lack of half-pitch band in resonant soft X-ray scattering. Another key findings of the model are predictions of I - N_TB and N_U - N_TB tricritical points and insight into biaxiality of N_TB.

What are the prerequisites for acquiring a stable twist-bend nematic phase (N_TB)? Addressing this question has led to the synthesis of a vast number of new compounds, concluding each time that the molecule's shape is one of the predominant factors. Inspired by the expanding knowledge of different achiral bent-shaped molecules forming a twist-bend nematic phase, we reinvestigate the interplay between a molecule's bend angle and a molecule's arms molecular biaxiality. Employing our previously developed generalized mean-field model, we explore more obtuse bend angles. We observe direct phase transition sequences between locally biaxial and uniaxial variants of N_TB, along with biaxial and uniaxial nematic phases. Additionally, we present a comprehensive overview of how phase diagrams evolve according to alterations in the value of the bend angle and the magnitude of biaxiality.

The results of Broadband Dielectric Spectroscopy and Differential Scanning Calorimetry of the 4-ethyl-4′-octylazoxybenzene (4EOB) liquid crystal are presented. Numerical analysis of the dielectric spectra results points to complex dynamics of the liquid crystal molecules in isotropic liquid, nematic and conformationally disordered crystalline phases. Two well-separated maxima on the imaginary part of electric permittivity were detected and described in liquid-like and crystalline phases. A third relaxation process, hidden in the conductivity region, describing conformational disorder of alkyl chains has been found in some plastic crystal phases. Temperature dependences of mean relaxation times characterising conformational disorder, flip-flop motions and rotation around long axis are of the Arrhenius type in liquid-like phases and conformationally disordered crystalline phases, and of the Vogel–Fulcher–Tammann type in the low-temperature crystalline phases for relaxation processes around short and long axis.

One of the interesting questions related to bent-shaped materials is how structural chirality of the twist-bend nematic ( ) phase can respond to the presence of molecular chirality, with later being introduced through chiral centers incorporated in the molecules or chiral dopants. We study this problem using minimal coupling Landau-de Gennes theory of , supplemented by a term representing intrinsic molecular chirality. Relative stability and properties of cholesteric ( ), chiral twist-bend nematic with heliconical structure ( ), and other homogeneous phases are studied. Besides nematic, chiral twist-bend nematic and cholesteric phases of vanishing global polarization, we find their polar analogues. In particular, a coupling between molecular chirality, alignment tensor and polarization fields can promote a globally polar and chiral twist-bend nematic ( ) with period comparable to that of .