Self-Assembled Liquid Crystal Nanostructures

Self-assembly of liquid crystalline molecules has been a highly interesting research area over the past few decades. The modification of traditional rod-like liquid crystalline molecules by adding additional functional groups is an effective way to obtain novel liquid crystal phases due to the segregation of incompatible molecular components, and this has been proved by various mesophases obtained from molecules which possess special shapes and structures. More recently, liquid crystalline molecules have been introduced to functionalize metallic nanoparticles to arrange these spherical particles into ordered structures. In this case, liquid crystalline molecules are grafted onto the surfaces of nanoparticles and the strong selfassembly ability of the molecules is the driving force for the ordered arrangement of nanoparticles. This method opens a new way to build spherical nanoparticles into untraditional nanostructures. Gold nanoparticles, due to their potential of building metamaterials that possess novel optical properties, such as negative refractive index and tunable surface plasmon resonance, is of great interest in this field of research. In this thesis, the self-assembly behaviour of a number of T-shaped liquid crystalline molecules have been investigated by small angle X-ray scattering (SAXS) and grazing incidence small angle X-ray scattering (GISAXS) methods and some complicated liquid crystal phases formed by T-shaped bolaamphiphiles have been solved. These T-shaped liquid crystalline molecules, each of which is composed of a biphenyl core ended by two terminal polar groups and a relatively long lateral chain, were found to form several novel structures which have never been realized in any liquid crystalline systems reported before. Using the same experimental methods, the self-assembled nanostructures of liquid crystalline molecules functionalized gold nanoparticles (GNPs) were also investigated. Different ordered superlattice structures including both 2D and 3D ones have been obtained from these hybrid systems. The results show how the mode of self-assembly of gold nanoparticles can be controlled by changing the parameters of coating molecules. Electron density maps of these structures were reconstructed using the diffraction intensities obtained from experimental results. The corresponding model of each structure was also proposed based on the reconstructed electron density maps as well as the structures and dimensions of molecules. Moreover, some simulation work was conducted, for example diffraction intensity simulation, diffraction pattern simulation and molecular dynamic III simulation, and good agreements between experimental and simulation results have been achieved. Finally, with the help of GISAXS technique the morphologies of double layers of gold nanoparticles prepared via layer-by-layer fabrication method have been investigated. By carefully adjusting the distance between adjacent gold nanoparticle layers, a successful control of the coupling of the localized surface plasmon polariton resonance was reported recently. In this thesis the sideway correlation of gold nanoparticles and the correlation between two gold nanoparticle layers were studied. The features observed in GISAXS patterns can be interpreted very well with relatively simple models.