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Title: Complex self-assembly of amphiphilic and polyphilic liquid crystalline compounds
Author: Lu, Huanjun
ISNI:       0000 0004 6495 3644
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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One of the most intriguing properties of liquid crystalline compounds is their ability to selfassembly into nanoscale entities, in the simplest cases as layers, columns, or spherical micelles, leading to their many applications in fields such as microelectronics, nanofabrication, medical etc. Understanding how such self-assembly can be controlled through molecular design is hence of paramount importance. Factors such as molecular shape and flexibility, interactions between different moieties, polarity and chirality all contribute to determine the exact mode of self-assembly of such a compound, as well as external controls through the use of temperature, solvent, electric and magnetic field. In this project three different series of compounds: X-shaped molecules, Polycatenar compounds, and Bolaamphiphiles with swallow-tailed side groups, were examined. Their complex modes of self-assembly have been studied using mainly X-ray diffraction methods, supplemented by Polarized Optical Microscopy, Differential Scanning Calorimetry, and for chiral phases Circular Dichroism Spectroscopy. In the X-shaped molecules, in addition to 'chess-board' two-coloured honeycomb columns with square cross-sections, several complex 3D phases with different tetragonal symmetries have been observed, their structures determined and molecular model constructed. In polycatenar compounds, we have studied the transitions from a recently found chiral isotropic phase (through dynamic mirror symmetry breaking of achiral compounds) to a bicontinuous cubic phase, either an achiral double network cubic or a chiral triple-network cubic phase. We have also found the formation of chiral SmQ phase in such achiral compounds, and have solved its structure - a long standing puzzle in liquid crystals for more than 30 years. In addition, a number of non-cubic phases, most of them suspected to be bicontinuous, have been identified and for most of them the space group symmetries have been determined, and tentative structural models proposed. In a number of bolaamphiphiles, with swallow-tailed side groups, a new single-diamond bicontinuous cubic phase has been discovered. The rigid aromatic cores are found to form bundles and such bundles form the segments of the single-diamond network with the side groups filling the rest of the space.
Supervisor: Zeng, Xiangbing ; Ungar, Goran Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available