A series of phenanthrene and oxidized phenanthrene derivatives with typical substitution patterns, 1.31, 1.32, 2.30a-f, 3.1a,b and (-)-4.1 have been synthesized as liquid crystal cores by a combined Directed ortho Metalation (DoM), cross coupling and Directed Remote Metalation (DreM) strategy. The synthetic methodology employed allowed variation of the tail and core structures, for the preparation of a new smectic liquid crystal compound (1.32), a homologous series of 9,10-dihydrophenanthrene-9,10-diones (2.30a-f), a diastereomeric trans-9,10-dihydrophenanthrene-9,10-diol (1.31), two enantiomeric 9,10-dihydrophenanthrene-9,10-diones (R)-3.1a-b) and an enantiomeric 9,10-dihydro-9,10-dimethylphenanthrene-9,10-diol ((-)-4.1). Polarized microscopic and differential scanning calorimetric measurements suggest that 1.31 forms a large range of SmC phase, ca. 100 ºC, followed by a small range of nematic phase, ca. 10 ºC; the 2.30a-f series show similar mesogenic properties, but with the extension of the length of a side chain from six carbons to eleven carbons, the nematic phase has disappeared (in the cases of 2.30a-c). Although (R)-3.1a-b and (-)-4.1 are not liquid crystals, they show ferroelectric induction by doping, in the amount of ca. 5 mol%, into unchiral liquid crystal hosts PhB, DFT, PhP1, NCB76 and 2.30f. However, due to the detection limit of the instrument, i.e., ca. 0.5 nC/cm2, the spontaneous polarizations (Ps) induced could not be measured. / Thesis (Ph.D, Chemistry) -- Queen's University, 2009-08-17 15:52:54.612

No description available.

Currently, alignment films for use in liquid crystal displays are produced via a mechanical rubbing process. The dust produced by mechanical rubbing along with problems due to friction and uneven roller pressure lead to defects in the display. Therefore a novel method for aligning polymers films by irradiation with polarised light has been attempted. Anisotropy introduced into the films by selective irradiation affects liquid crystal alignment. The polymers used in this study are poly (vinyl cinnamate), poly (9- anthraceneoate ethyl methacrylate) and poly (p-azidobenzoate ethyl methacrylate). Poly (vinyl cinnamate) is a classical photoresist polymer which undergoes a [2+2] photocycloaddition in the presence of UV light. Poly (9-anthraceneoate ethyl methacrylate) and poly (p-azidobenzoate ethyl methacrylate) are both novel polymers which have the potential to undergo photo-crosslinking reactions. Poly (9-anthraceneoate ethyl methacrylate) contains an anthracene-terminated side chain which dimerises under the influence of UV light introducing anisotropy into the system. Poly (p-azidobenzoate ethyl methacrylate) contains an azido group which when irradiated with polarised light loses nitrogen to yield nitrenes which can combine to form azobenzene species. UV spectroscopy, infrared dichroism studies, birefringence measurements and fabrication of a simple liquid crystal cell show that poly (vinyl cinnamate) and poly (9-anthraceneoate ethyl methacrylate) undergo selective photoreaction. Poly (p- azidobenzoate ethyl methacrylate) is shown to undergo reaction but not to give the desired products.

No description available.

Solvent-mediated self-assembly of nanoparticles is an effective and efficient way for the bottom-up organization of functional structures. The primary object of this work is to build up a model system for the study of suspensions of disk-shaped nanoparticles, and use it for the study of self-assembly and discotic liquid crystal phase transitions of discotic particles. The work was introduced by the control over the size and polydispersity of zirconium phosphate (ZrP) disks through synthesis. Systematic experiments revealed that regular-shaped α-zirconium phosphate crystalline disks with a size-to-thickness ratio from 1 to 50 and size polydispersity as low as 0.2 can be obtained through hydrothermal treatment in 3 M to 15 M phosphoric acid solutions. Transmission and scanning electron micrographs revealed that the growth of the disks is mediated by oriented attachment, which happened continuously throughout the hydrothermal treatment between various sized disks. Ostwald ripening is effective in improving the regularity of the shape of the disks, especially under prolonged hydrothermal treatment. Under the microwave assisted hydrothermal conditions, the rate of attachment on the flat surfaces of the disks is accelerated, which leads to the formation of the column-shaped crystals. With the ability to adjust the size, aspect ratio, and polydispersity of ZrP disks, the study on self-assembly behavior and the discotic liquid crystal phases was enabled. Firstly, liquid crystal phases of aqueous suspensions of ZrP disks were investigated. Iridescent smectic phase and the critical points of phase transitions were found. Moreover, monolayer ZrP nanosheets with extremely high aspect ratio, which were achieved by exfoliating the ZrP crystals, were also used in this study. The high aspect ratio of nanosheets produces a laminar phase at low nanosheet concentration. Chiral liquid crystal phases were demonstrated when increased the concentration of the nanosheets. The competition between the chirality and layering leads to twisted and layered structures. For the final part, solvent-mediated self-assembly of disks and nanosheets via undulation of liquid crystal phases showed an interesting approach for bottom-up design of functional nano-structures.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references. Also available in electronic version.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

In this project a number of synthetic procedures were investigated with a view to preparing a new type of charge transfer polymer system having a structure based on that of side chain liquid crystal polymers, in that the hoped for polymer was composed of charge transfer acceptors connected to a polymer backbone via a flexible alkyl spacer linkage. As part of this work new charge transfer complexes were prepared some of which have shown possible novel properties, such as, co-operative magnetic effects and film forming capabilities. Finally, in order to characterise materials prepared, a Faraday magnetic susceptibility balance and instrumentation for measuring electrical conductivity has been built.

In 1970, Freiser made the theoretical prediction that a biaxial nematic phase could exist. In auniaxial nematic, only one particle axis is aligned but with a biaxial nematic, all three molecular axes are aligned. This phase is expected to occur for particle whose shape is intermediate between that of a disc and a rod. Board and bent-core particles are examples of such structures. Despite extensive experimental investigation, however, very few biaxial nematic systems have been found. Yu and Saupe [21] have shown the occurrence of a biaxial nematic phase generated for a lyotropic system. Similarly van der Pol observed a biaxial nematic phase in a colloidal suspension of board-like goethite particles [22]. For thermotropic, molecular systems, however, the situation is less clear-cut. Merkel et al., [23] and Figueirinhas et al., [24] claim that Tetrapodes have can exhibit a biaxial nematic phase, whilst Acharya et al., [25] and Prasad et al., [26] have also suggested the occurrence of this same phase with bent-core molecules, though experimental uncertainty still exist. With regards to theoretical predictions of the biaxial nematic transition, one notes in particular the work of Taylor and Herzfeld [13] on hard sphero-platelets, which predicts a rich phase diagram, notably containing an unusual discotic smectic phase. To date there are few simulations of board-like models, such as Vanakaras et al., [27] being arecent exception, developing a phase diagram for hard board-like colloids. Similarly, Escobedo[28] has produced a phase diagram of hard cuboids. We present molecular dynamics simulation results on a short range repulsive fused-hexagonmodel, somewhat resembling hard boards. Depending on the geometry of the board, we observe uniaxial and biaxial nematics, smectics A and C, a biaxial smectic phase and a columnar phase. Possibly the most interesting result is the existence of the theoretically predicted discoticsmectic. We further investigated the effect of applying both external fields and shears to several of the structures. The former, among other things, aided the alignment of the particles in the phase, removing dislocations. The shear was also seen to increase biaxial ordering, however, it also demonstrates an ability to introduce clear layer fractures, seen when shearing forces became overly dominant. An applied electrical field was able to induce isotropic!biaxial nematic and biaxial smectic switching. Finally we consider briefly less-symmetric arrangements of fused hexagons, including chiral particles. These systems proved hard to equilibrate but discotic nematic phases were observed for certain structures. Chiral clusters were also observed, however, no globally chiral phase was found. Columnar structures were also seen, but showing a weak overall alignment as columnstended to point along several directions.

The motions of particles dispersed in liquid crystals can be influenced by the application of an electric field, the effect depending on the field frequency and field amplitude. Sandwich cells under the application of electric field are widely used as the tool in order to investigate the fundamental research relating to electro-optic display technology. Therefore, the aim of this experimental work is to find and investigate novel motion of the particles dispersed in the liquid crystal phases, held within a sandwich cell. For the liquid crystal–particle systems in the sandwich cells in this thesis, the particle shapes, temperature and cell geometry are all shown to have an influence on the regime of the particle’s motions, with different phenomena observed using three different phases of liquid crystals. The experiments are designed to find and investigate the novel motion of the micron sized silica particles in the liquid crystal phases. In the chiral nematic phase, spherical particles are shown to exhibit linear motion, which is related to the electrophoretic mobility. Such spherical particles are also observed to show circular motion which is found to have a field dependency that can be related to Quincke rotation. A maximum frequency for motion occurs which is found to possibly be related to the effect of the ion diffusion in the liquid crystal-particle composite system. The direction of the circular motion is found to be independent of the handedness of the chiral nematic material. In the isotropic phase of a chiral nematic liquid crystal, the spherical particles do not exhibit any linear motion, which shows the system does not follow the traditional electrophoresis observed in normal isotropic liquids. The circular motion of the spherical particle that is observed in the isotropic phase is analysed in terms of the Quincke rotation and again shows the Maxwell relaxation time. The electric-field induced motion of elongated particles in four different nematic systems is examined. In this case of planar aligned systems, linear motion is observed, in which the velocity shows a minimum for particles of the same length as the cell gap. A novel field-induced defect texture appears in the homeotropic device containing a nematic liquid crystal of negative dielectric anisotropy. Interestingly, the motion of the particle is found to be strongly coupled with the defects formed.