Twist-bend nematic phases of bent-shaped biaxial molecules

Abstract

How change in molecular structure can affect relative stability and structural properties of the twist-bend nematic phase (N$_\text{TB}$)? Here we extend the mean-field model [C. Greco et al., Soft Matter, 2014, 10, 9318] for bent-shaped achiral molecules, to study the influence of arm molecular biaxiality and the value of molecule's bend angle on relative stability of N$_\text{TB}$. In particular we show that by controlling biaxiality of molecule's arms up to four ordered phases can become stable. They involve locally uniaxial and biaxial variants of N$_\text{TB}$, together with the uniaxial and the biaxial nematic phases. However, the V-shaped molecule show stronger ability to form stable N$_\text{TB}$ than a biaxial nematic phase, where the latter phase appears in the phase diagram only for bend angles greater than $140^\circ$ and for large biaxiality of the two arms.