Liquid crystals are a promising class of materials used in or proposed for a wide variety of applications, ranging from liquid crystal displays and light emitting diodes to photovoltaic devices and field effect transistors. Many molecular level structural features are known to influence the properties of liquid crystalline materials, but the outcome of this influence is often poorly understood. A strategy was developed for the formation of elliptical mesogens having a shape intermediate between the well-known rods and discs by rigidly linking two disc-shaped molecules. These studies have led to investigations of structure-property relationships in discotic and elliptical mesogens, including not only the effect of shape and overall symmetry, but also the influence of the presence and position of a nitrogen atom in the core, the location of functional groups, and the length of alkoxy chains. Disc-shaped molecules were assembled through the condensation of 2,3,6,7-tetrakis(alkoxy)phenanthrene-9,10-diones with diamines, allowing the preparation of mesogens bearing a wide variety of functional groups. A simple and inexpensive capillary furnace was developed to improve and facilitate the study of liquid crystalline materials using variable temperature X-ray diffraction. Two of the systems studied appear to form elliptical mesogens through hydrogen bonding, and it was found that elongation of the mesogen shape from a disc to an ellipse promotes the formation of nematic and rectangular columnar phases, as well as supercooling of the columnar phases resulting in columnar ordering at room temperature. The formation of non-elliptical dimers of discs was attempted in two different ways, but in both cases, no rigidly-linked dimers were observed in the mesophases. However, one of these systems was found to result in solution self-assembly and in hexagonal columnar phases stable over remarkably broad temperature ranges, which appears to be the result of hydrogen bonding within the columns.

Columnar liquid crystals have emerged as a promising class of materials for light emitting diodes, photovoltaic devices and field effect transistors. In addition to their practical importance, the ability of disc-shaped molecules to spontaneously form columnar nanostructures represents a striking example of self-assembly driven largely by ∏-∏ interactions. Any factor that alters the strength of ∏-stacking between neighbouring molecules should therefore have a dramatic impact on the propensity of these molecules to form columnar mesophases. Studying the relationship between a molecule's structure and its tendency to self-assemble into columns can thus provide valuable insight into the nature and strength of noncovalent interactions between discotic mesogens in addition to facilitating the design of new liquid crystalline materials. A series of disc-shaped molecules was produced by the condensation of 1,2-diamines with 2,3,6,7-tetraalkoxy-phenanthrene-9,10-diones in order to systematically investigate the relationship between changes in molecular structure and the self-assembly of columnar liquid crystalline phases. Functional groups were found to have a pronounced effect on the tendency of these molecules to self-assemble. Moreover, the thermal stability of these columnar phases was very sensitive to the position of the substituents and their electron withdrawing ability, with the columnar-to-isotropic transition temperature strongly related to Hammett Ơ-parameters of the functional groups. The effect of core size were also investigated through the preparation of molecules containing 4-, 5- and 6-membered fused aromatic rings. The effects of heteroatoms in the aromatic core were also explored. Phase behaviour had a striking dependence on both the number and position of heteroatoms in the core. Furthermore, substituting hexaalkoxy-[a, c]dibenzophenazine with different lengths of pendant chains showed that changing molecular symmetry and shape had an effect on the phase behaviour of discotic mesogens.

In the field of material science, structure/property relationships can allow a more efficient design of materials exhibiting the desired properties. Self-assembled super-structures possess several advantages that can be exploited. The formation of complex architecture is dictated by the properties of the small sub-units. The formation of liquid crystalline phases requires molecular anisotropy, which is often achieved by using flat rigid rod or disc-shaped cores decorated with aliphatic chains. Other structural morphologies have also proven to allow the formation of these ordered fluid phases: plate, bent-core, bowl etc. Our research group is interested in disc-shaped molecules that have the ability to form liquid crystalline phases constituted of columns distributed in a two-dimensional lattice. The discs within a column are stacked on top of each other that could be used to conduct either energy or charges. The research projects presented in this thesis were concerned in establishing the effect of molecular symmetry and shape on the mesogenic properties of compounds based on a dibenz[a,c]phenazine core decorated with alkoxy chains (four and six). Series of structural isomers have been synthesized and their mesogenic behaviour analyzed. Reducing the molecular symmetry of mesogens lowers the melting temperature and, to a smaller extent, the clearing temperature leading to broader liquid temperature ranges of mesogenic behaviour. To study the effect of molecular shape, compounds with chains of different length and different motifs were prepared. This type of substitution leads to different mesogenic behaviour. Comparisons between structural isomers showed that this new substitution pattern lowered the clearing temperatures for these mesophases. The molecular shape of these compounds does have an effect on the mesophase and the results could allow more efficient engineering of systems used in various devices.

This multi-authored book includes selected contributions reviewing the results achieved in the synthesis and characterization of organized polymeric materials. The focus is on competitive materials with liquid crystalline or electroconductive properties. The fine tuning of the properties offered by advanced chemical synthesis has been investigated by a large number of state-of-the-art techniques, including both microscopic (ESR, NMR, dielectrometry, fluorescence, IR, Raman spectroscopy) and macroscopic (calorimetric, mechanical) methodologies. The book also provides an updated coverage of the most challenging applications of organized polymers as functional materials in the fields of electrooptical devices, information retrieval and organic electroconductors.

Liquid crystals are partially ordered systems without a rigid, long-range structure. The study of these materials covers a wide area: chemical structure, physical properties and technical applications. Due to their dual nature — anisotropic physical properties of solids and rheological behavior of liquids — and easy response to externally applied electric, magnetic, optical and surface fields liquid crystals are of greatest potential for scientific and technological applications. The subject has come of age and has achieved the status of being a very exciting interdisciplinary field of scientific and industrial research.This book is an outgrowth of the enormous advances made during the last three decades in both our understanding of liquid crystals and our ability to use them in applications. It presents a systematic, self-contained and up-to-date overview of the structure and properties of liquid crystals. It will be of great value to graduates and research workers in condensed matter physics, chemical physics, biology, materials science, chemical and electrical engineering, and technology from a materials science and physics viewpoint of liquid crystals.

The Encyclopedia of Physical Chemistry and Chemical Physics introduces possibly unfamiliar areas, explains important experimental and computational techniques, and describes modern endeavors. The encyclopedia quickly provides the basics, defines the scope of each subdiscipline, and indicates where to go for a more complete and detailed explanation. Particular attention has been paid to symbols and abbreviations to make this a user-friendly encyclopedia. Care has been taken to ensure that the reading level is suitable for the trained chemist or physicist. The encyclopedia is divided in three major sections: FUNDAMENTALS: the mechanics of atoms and molecules and their interactions, the macroscopic and statistical description of systems at equilibrium, and the basic ways of treating reacting systems. The contributions in this section assume a somewhat less sophisticated audience than the two subsequent sections. At least a portion of each article inevitably covers material that might also be found in a modern, undergraduate physical chemistry text. METHODS: the instrumentation and fundamental theory employed in the major spectroscopic techniques, the experimental means for characterizing materials, the instrumentation and basic theory employed in the study of chemical kinetics, and the computational techniques used to predict the static and dynamic properties of materials. APPLICATIONS: specific topics of current interest and intensive research. For the practicing physicist or chemist, this encyclopedia is the place to start when confronted with a new problem or when the techniques of an unfamiliar area might be exploited. For a graduate student in chemistry or physics, the encyclopedia gives a synopsis of the basics and an overview of the range of activities in which physical principles are applied to chemical problems. It will lead any of these groups to the salient points of a new field as rapidly as possible and gives pointers as to where to read about the topic in more detail.

The commercial availability and decreasing cost of polyhedral oligomeric silsesquioxanes in recent years has opened up the field to everybody who wishes to apply these unique properties in their own technologies. This is the first book to provide a comprehensive overview of these applications, and covers the synthesis, characterization and history of polyhedral oligomeric silsesquioxanes, their use as metallasilsesquioxane catalysts, their effect upon polymer properties and plastics performance, and their use in superhydrophobic nanocomposites, and electronics, energy, space and biomedical applications. "Applications of Polyhedral Oligomeric Silsesquioxanes" is a valuable reference for those working across a range of disciplines, including chemists, materials scientists, polymer physicists, plastics engineers, surface scientists, and anybody with a commercial or academic interest in plastics, composite materials, space materials, dental materials, tissue engineering, drug delivery, lithography, fuel cells, batteries, lubricants, or liquid crystal, LED, sensor, photovoltaic or biomedical devices.