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Title: Molecular simulation studies of chromonic mesogens in aqueous solution
Author: Thind, Romnik
ISNI:       0000 0004 6497 6846
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2018
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This thesis focuses on understanding the aggregation behaviour of lyotropic chromonic liquid crystals in aqueous solution. Molecular simulation methods are used to provide structural and thermodynamic information on the self-assembly of chromonic mesogens, and the results used to re-interpret data from previous experimental studies of these systems. Extensive atomistic level molecular dynamic simulations have been performed on three chromonic dyes in solution: 5,5'-dimethyoxy-bis-(3,3'-di-sulphopropyl)- thiacyanine triethylammonium salt (Dye A), 5,5'-dichloro-bis-(3,3'-di-sulphopropyl)- thiacyanine triethylammonium salt (Dye B), and Bordeaux dye. The results are compared to key experimental data, such as X-ray scattering and cross-sectional areas and aggregation free energies. Previously suggested chromonic aggregation models, such as a double-width column and a brickwork layer structure, have been discounted based on the simulation results. Instead the simulations of dyes A and B demonstrate an anti-parallel stacking arrangement providing columns in which solubilizing sulphonate groups lie on alternate sides of the column as the column is traversed. In addition, a new type of chromonic smectic layered phase is predicted for these molecules. For dye A, a novel chiral column structure is seen within isolated columns in isotropic solution. For Bordeaux dye a stable single-molecule column is seen, along with a number of meta-stable structures including a double-width column in which two single-molecule columns are linked via a salt bridge. In an attempt to simulate larger time and length scales, two bottom-up coarsegraining techniques, iterative Boltzmann inversion (IBI) and force matching (FM), were tested on simple hexane/water systems and then applied to Dye A. Both of these methods proved to be largely unsuccessful in reproducing the same aggregation behaviour seen in the atomistic simulation work.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available