This thesis is concerned with the determination of the director profile within a nematic liquid crystal cell from optical experiments. The larger part of the work details the de- velopment of computational methods which can be used to find the director profile, and the application of these tools to the fully leaky guided mode experiment. In a second part, a simple conoscopic device is built, and then used to undertake a novel viscodynamic experiment. In essence, the fully leaky guided mode experiments and its relatives measure the de- pendence of the transmission and reflection coefficients of a liquid crystal cell upon incident angle. It is simple enough to calculate these coefficients if the director profile is known, but experimentalists actually need to achieve the opposite. That is, having measured the transmission and reflection coefficients, they must determine the director profile. However, this turns out to be an ill-posed problem, and so some additional information about the director profile is required. There is indeed an appropriate source of additional information - the continuum theory of nematic liquid crystals - and it is exploited here to develop two computational tools. In the first, it is used to adapt a mathematical technique, Tikhonov regularization, to both steady-state and time-dependent situations, so that director profiles can be recov- ered having made only weak assumptions about their behaviour. A second tool makes stronger assumptions and can be deployed after the first to estimate some of the unknown parameters which appear in the continuum theory. These tools are use in the first instance to analyze data drawn from two fully leaky guided mode experiments. In the first experiment, a hybrid aligned cell was measured during AC switching, and from its data director profiles and several phenomenological parameters including four viscosities are determined. Following that, the DC switching of the same cell is studied, which turns out to be critically affected by the motion of tiny concentrations of charged impurities. Then, having noted that only limited information about the director profile can be recovered from even the most elaborate optical experi- ment, a conoscopy experiment is designed to recover it quickly. Following this approach, a previously unknown flow-induced transition between topologically distinct states in a homoetropically aligned cell is observed.

The discovery of discotic liquid crystals in 1977 by Chandrasekhar has led to an ever increasing interest in the preparation of new discotic mesogens. Research on the potential application of such systems has, however, been held back mostly by synthetic and purification difficulties to obtain enough of the required pure materials. The work described in this thesis (Chapter 2) concerns the synthesis of macrodiscotic structures which led to the formation novel discotic liquid crystalline systems. Nonplanar substituted phthalocyanines have been described by Simon and were found to be mesogenic. We expected that planarising these systems (formation of triphenylene) would have the effect of changing both the absorption (shift to longer wavelength due to extra conjugation) and the mesogenic properties (due to formation of large discs). The syntheses of triphenylenophthalocyanines were achieved using palladium catalysed aryl-aryl cross-coupling as key step in the syntheses. The end materials were characterised and tend to be mesogenic. After the successful synthesis of the triphenylenophthalocyanines, we were in a position to further extend the n-system of our phthalocyanines and the molecules targeted were perylenophthalocyanines (Chapter 3). The syntheses were achieved through a cyc1oaddition reaction as key step. In this case, however, none of the perylenophthalocyanines were liquid crystalline. 3: 1 phthalocyanines were also prepared and tend to be non-mesogenic. A senes of mixed hexyloxy-Ihexylthio-triphenylenes has also been synthesised to determine the structural features governing the formation of helical mesophases shown by HHTI (Chapter 4). It has been shown that four sulphide substituents (plus two alkoxides) are required to induce the additional, more ordered phase. Furthermore, the position of substitution is crucial for its formation. Also, the synthesis and characterization of a series of triphenylenes has been described in which 2, 4 or 6 of the alkyloxy chains of parent hexa(hexyloxy)triphenylene are replaced by heptyl chains (giving mixed alkyl-alkyloxy triphenylenes). This series provides a direct comparison to the derivatives which gives to the rare helical phase. Finally, the synthesis of a few novel triphenylene molecules expected to be on the boundaries between the traditional rod-shaped and disc-shaped structure were achieved. Some of these compounds formed discotic mesophases.

No description available.

The electrospinning technique transforms a polymer solution of sufficient concentration from a sub-millimetre sized droplet to a fibre ranging in diameter from tens of micrometers to tens of nanometres by application of a sufficiently strong electric field. A polymer jet is extruded from the droplet and a solid fibre is deposited onto a grounded collector. During this transition a large scale transformation occurs and the solvent is rapidly removed from the polymer jet. The purpose in this investigation is to develop a model of how the polymer chain conformation is altered from the solution state to that of the fibre by the electrospinning process using the technique of small angle neutron scattering (SANS). Using SANS in conjunction with isotopically labelled samples the polymer chain conformation in high dielectric constant solvents was measured at the high concentrations, associated with electrospinning. It was determined that for the concentrations used in electrospinning in this work, the solutions were all in the semi-dilute state, meaning that the polymer chain was in a swollen conformation and its dimensions were greater than those in the bulk state. The chain conformation in the polymer fibres was also measured with the aid of SANS and was determined to exhibit chain dimensions comparable to that measured in the solution. The level of extension inherent to the electrospinning process was measured by collection of aligned fibres. It was determined that the chains extend ~5% parallel to the fibre axis. A relatively small extension compared to the large macroscopic transformation of the fibre. The level of extension was further increased to ~20% through mechanical deformation by use of a rotating collector. The polymers relaxation rate, the solvent evaporation rate and any formation of a polymer skin play a significant role in determining the level of molecular anisotropy in the fibres.

This thesis considers the mathematical modelling of smectic A liquid crystals under the application of certain external influences, using the recently developed continuum dynamic theory for smectic A liquid crystals by Stewart (2007). This theory is used extensively throughout and is of crucial importance when determining our results in a variety of situations.

In this thesis, the fluid dynamics of smectic A and smectic C liquid crystals are considered under a variety of experimental and theoretical situations. The smectic A liquid crystals are modelled by the recent dynamic continuum theory proposed by Stewart. The smectic C liquid crystals are modelled, in general, by the continuum dynamic theory proposed by Leslie, Stewart and Nakagawa with some additions made following the work of de Gennes.

No description available.

The Rotman lens is a beam former which is attractive due to its wide bandwidth, wide angular cove rage, planar nature and simple fabrication. Its angular resolution is limited because only a discrete number of steering angles (equal to the number of input ports) can be achieved. This limitation is overcome using a new type of RetroDlrective Array {RDAJ based on the a Rotman lens, and a Rotman lens used in conjunction with liquid crystal (LC) phase shifters to provide reconfigurable radiation patterns. Parametric studies into the geometry of the lens were first carried out to develop design guidelines. A new type of RDA based on the Rotman lens was designed which requires additional features not normally considered in conventional operation of the lens. A prototype Rotman lens based RDA was fabricated and experimental measurements of the monostatic and bistatic radar cross-section patterns were used to demonstrate continuous angular coverage of ±40° in azimuth over an 8 -12 GHz f requency range. A new low loss GT3-24002 liquid Crystal (l C) developed by Merck was used to fabricate inverted microstrip line based LC phase shifters, with figures of merit of up to 110• phase shift per dB of loss were measured over a 6 -10 GHz frequency band. These devices were integrated into the array feed circuitry of a Rotman lens to implement a reconfigurable beamforming network which exhibits significantly higher angular resolution than conventional Rotman architectures. Beams centred at 0•, ±l5• and ±30°, were switched between monopulse sum and difference pattern operation over 6 - 10 GHz by applying suitable voltages to the LC lines to provide phase shifts of O• and 180•, and in addition, the dynamic phase responses at the outputs of the LC lines were varied to continuously scan the radiation patterns over an angular range of ±39°.

Mura is a type of defect on LCD's that affects image quality. Due to its subtle nature - gradually and non-uniformly changes in lightness within a specific area, how Mura defects can be effectively inspected and objectively graded has been an issue in the LCD manufacturing industry for many years. Although many studies using different approaches to the Mura detection issue have been carried out, there is still a lack of reliable standard and methods that can be fully adopted in the industry and replace the human eye in the inspection work. Based on demand from the LCD industry, a uniform Mura detection model is needed to provide a stable and reliable inspection system for image quality judgment. For many years, researchers have studied this topic by using uniform colour patches. Few of them extended investigations to conditions where Mura defects are viewed against complex images in background. This might be the first time that study of Mura detection has been extended to patterned and complex image backgrounds. There are four experiments in this study. Influences of colour, Mura size and the masking effect caused by background patterns on Mura detection were investigated. Among them, masking effect is the dominant factor that significantly affects the detection thresholds. Our analyses show that the influence of Mura size was mild for noise backgrounds. Orientations of the Mura patterns had no effect for uniform and noisy backgrounds, though some other studies of visual acuity and contrast sensitivity in humans have shown an unequal sensitivity across orientation. Although colours showed little effect in this study, some seemed to produce more stable results. Particularly for uniform backgrounds, colour and size caused problems for some observers who were unable to maintain consistent thresholds for Mura detection. Mura detection against still and moving pictorial backgrounds were also studied. It seems that the human visual system uses different strategies with different mechanisms to detect Mura patterns on uniform, patterned and pictorial backgrounds respectively. On uniform backgrounds, the human visual system uses colour difference, lightness difference and boundary detection theorem to discern a Mura pattern whereas detecting Mura patterns on patterned backgrounds is highly affected by the masking effect. For static pictorial backgrounds, detecting Mura patterns even relies very much on cognition and thus causes huge problems for observers to recognize them. This situation only improves when the position correlation between a Mura pattern and its background changes from static to dynamic; and it is until then detecting Mura patterns seems to be a quantifiable task again. A Mura detection model was constructed based on knowledge of the human visual system, which is mainly concerned with how a static image pattern projected on the retina is converted into neural signals, and how these signals are interpreted by our brains. Our analyses show that the model delivers more reliable results than the S-CIELAB model when masking effect take places.

In this thesis, the physical properties of disco tic liquid crystals have firstly been studied but the main focus concerns an investigation of photoconduction properties of liquid crystals using the Time-ofFlight (ToF) method. Photoconduction ofHAT6, HAT6-NOz and 8H2Pc have been reinvestigated. These materials show good ToF signals and the transit times can obviously be determined. The mobility of each compound agrees well with that reported in the literature. HAT6 shows temperature independence of hole mobility over the entire mesophase range. In contrast, the hole mobility of HAT6-N02 increases with increasing temperature and this supports the hopping conduction model. Interestingly, 8H2Pc shows very short transit time and provides a high hole mobility value (10-' cm2y-'s'). The hole mobilities of HHTT in the Colh phase determined from various systems are in reasonable agreement with those reported in the literature. Increasing the temperature results in decreasing of the hole mobility. This suggests a band conduction mechanism. The laser power strongly influences both the shape and the transit time of the ToF signals obtained from HHTT. This behaviour is ascribed to a space charge effect and measured signals agree qualitatively well with those simulations previously run by Leon Lever using a Monte Carlo method. HTTT shows an Onsager-type mechanism of photocharge generation. At low light intensities the quantum yield is in the range of 10-4. The ToF photoconduction ofH7T shows good transit shapes and a hole mobility of 2.5xl0's cm2V's' was found. The addition of an extra hexyloxy (C6H130) group into the HAT6 structure results in a decrease of the transition temperature and a lowering of the el~ctronic conduction. The ToF photoconduction of quinone-HAT6 shows good ToF signals having the transit times in the range of hundreds of microsecond. A hole mobility value of 8.1 x 1 0-scm2V-' s-' was obtained. Chare carrier transport of Octa(5-methylhexyl)phthalocyanine has been investigated by the ToF method and it shows good ToF signals. A very high hole mobility value of 0:14 cm2V-'s-' was obtained. This value is slightly higher than that observed in octaoctylphthalocyanine (8H2Pc) (10-' cm2V-'s-'). ToF photoconductions ofHABT8 and chloroquinone-HAT6 were attempted. Unfortunately, the loglog plots of the ToF signals obtained from both materials did not show clear transit times. As a result, detennination of the hole mobility over the meso phase range is hard to achieve. A charge injection study of some triphenylene-based discotic liquid crystals has been made. Unfutunately, neither Schottky model nor Bardeen model can be used to explain the barrier heights at the metallDLC interfaces. This suggests .that the alternative model is needed.