Chiral Fluctuations and Structures

TL;DR

This paper explores how chiral molecules influence fluctuation-induced optical effects and structural phases in mesophases, revealing conditions for novel defect-rich lamellar states similar to twist-grain-boundary phases.

Contribution

It introduces the concept of fluctuation-induced rotary power in chiral systems and predicts new defect-riddled lamellar phases under certain conditions.

Findings

Chiral fluctuations induce non-zero rotary power.

Achiral and chiral systems exhibit different fluctuation behaviors.

Conditions for defect-rich lamellar phases are identified.

Abstract

Chiral molecules form a number of non-chiral structures, the simplest being an isotropic fluid phase. In a mesophase of achiral molecules the fluctuations will on average be achiral as well: left-handed twists and right-handed twists will occur with the same probability. In a system composed of chiral molecules, however, the fluctuations will be biased in one direction or the other, and there will be optical effects such as a non-zero fluctuation induced rotary power {\sl in addition} to the molecular rotary power of the individual molecules. We discuss this effect in a number of contexts, including lyotropic lamellar phases. When the tendency to twist is strong enough or the line energy of having an exposed edge is small enough, a new, defect riddled ground state of a lyotropic lamella, akin to the Renn-Lubensky twist-grain-boundary phase of thermotropic smectics, can occur.