Modulated nematic structures induced by chirality and steric polarization

TL;DR

This study uses Landau-deGennes theory extended for molecular polarization to predict new one-dimensional modulated nematic structures in both chiral and nonchiral bent-core and dimeric liquid crystals, revealing four novel phases.

Contribution

It introduces four new bulk ODMNS, including two previously unreported structures, and explores how chirality influences their stability and formation.

Findings

Four new bulk ODMNS identified, including $N_{LP}$ and $N_{TP}$ phases.

Chirality converts certain nonchiral phases into twist-bend nematic phases.

Nonchiral $N_{LP}$ phase remains stable even with molecular chirality.

Abstract

What kind of one-dimensional modulated nematic structures (ODMNS) can form nonchiral and chiral bent-core and dimeric materials? Here, using Landau-deGennes theory of nematics, extended to account for molecular steric polarization, we study a possibility of formation of ODMNS, both in nonchiral and intrinsically chiral liquid crystalline materials. Besides nematic and cholesteric phases, we find four bulk ODMNS for nonchiral materials, two of which have not been reported so far. These new structures are longitudinal ($N_{LP}$) and transverse ($N_{TP}$) periodic waves where the polarization field being periodic in one dimension stays parallel and perpendicular, respectively, to the wave vector. The other two phases have all characteristic features of the twist-bend nematic phase ($N_{TB}$) and the splay-bend nematic phase ($N_{SB}$), but their fine structure appears more complex than that considered so far. The presence of molecular chirality converts nonchiral $N_{TP}$ and $N_{SB}$ into new $N_{TB}$ phases. Interestingly, the nonchiral $N_{LP}$ phase can stay stable even in the presence of intrinsic molecular chirality. Exemplary phase diagrams provide further insights into the relative stability of these new modulated nematic structures.