Hidden traces of chirality in the fluctuations of a fully unwound cholesteric

• Published in: Soft matter 2023-02, Vol.19 (6), p.1115-113
• Main Author: Poy, Guilhem
• Format: Article
• Language: English
• Subjects: Chirality; Condensed Matter; Decay; Destabilization; Fluctuations; Hydrodynamics; Light scattering; Liquid crystals; Physics; Soft Condensed Matter
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/d2sm01646j

Confinement and hydrodynamic interactions often play an important role in the fluctuation dynamics of soft matter systems, which can typically be studied using light scattering techniques. With experimental and theoretical methodologies, I demonstrate here that chirality is an additional critical parameter that leads to diverging decay times and correlation lengths in chiral liquid crystal cells with a fully unwound cholesteric helix. This study combines light scattering measurements made in a tailored microscope geometry and theoretical calculations of the decay dynamics of chiral orientational fluctuations-including hydrodynamics-to establish the existence of two soft chiral modes of fluctuations driving the destabilization of the unwound cholesteric. Despite the achirality of the equilibrium state of unwound cholesterics, this study indicates that chirality hides itself in the orientational fluctuation modes and plays a major role in their dynamics, which can be exploited to locally measure the strength of chirality in frustrated chiral liquid crystal cells. I show here that chirality introduces twist in the fluctuations of a fully unwound cholesteric layer, which are characterized by a critical slowing down of the decay frequencies when the concentration C of chiral molecules is increased.