Directing structure through chirality

Thesis

Chirality - or the absence of mirror symmetry - is a fundamental physical property that permeates geometrical structures in nature, from the double-helical shape of DNA to the macroscopic anatomy of entire organisms. However, the specific mechanisms underpinning the propagation of chirality across such wide differences in length-scales often remain poorly understood. In this thesis, we explore the quantitative link between molecular and supramolecular chirality in liquid crystal phases of elongated polymers, which are ubiquitously observed in both biological and artificial colloidal solutions. We investigate the self-assembling behaviour of such systems through the combination of detailed numerical simulations and classical density functional theory in the Onsager formalism. The quantitative accuracy of the latter and of its various extensions is thoroughly assessed in the case of both rigid and flexible particle models, and rigorous first-principle derivations of its underlying mathematical framework are systematically provided. An original virial integration scheme based on hierarchical bounding volumes is also introduced to accelerate non-bonded interaction energy computations by several orders of magnitude for complex, highly-anisotropic molecular systems. These developments allow us to tackle the cholesteric assembly of DNA origamis using a structurally- and mechanically-realistic representation of the particles, and enable us to provide theoretical evidence of a novel mechanism of chirality amplification in liquid crystals, whereby phase chirality is governed by fluctuation-stabilised helical deformations in the conformations of their constituent molecules. Our results compare favourably to recent experimental measurements and demonstrate the influence of intra-molecular mechanics on chiral supramolecular order, with potential implications for a broad class of experimentally-relevant colloidal systems.

Authors: Tortora, M

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: DNA nanotechnology; Cholesteric phases; Molecular modelling; Chirality; Self-assembly
• Subjects: Statistical mechanics; Polymer colloids; Liquid crystals; Density functionals; Chemistry, Physical and theoretical