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Articles by Michael Hird
Total Records ( 4 ) for Michael Hird
  Philip J. Stackhouse and Michael Hird
  A series of novel symmetrical and unsymmetrical triphenylene-based discotic liquid crystalline materials with one or six branched peripheral alkoxy chains have been prepared. These materials have been compared with analogous known symmetrical and unsymmetrical compounds to reveal a balance between steric and space-filling effects of the peripheral branched chains, which significantly affects intermolecular forces of attraction and packing, and hence affects melting and isotropisation temperatures of the liquid crystalline materials. The desired result of reduction of melting points and enhancement of isotropisation temperatures has been accomplished by use of branched alkoxy chains in both symmetrical and unsymmetrical materials.
  John W. Goodby , Isabel M. Saez , Stephen J. Cowling , Julita S. Gasowska , Robert A. MacDonald , Susan Sia , Paul Watson , Kenneth J. Toyne , Michael Hird , Robert A. Lewis , Seung-Eun Lee and Valerij Vaschenko
  In this article we investigate the complexity of the molecular architectures of liquid crystals based on rod-like mesogens. Starting from simple monomeric systems founded on fluoroterphenyls, we first examine the effects of aromatic core structure on mesophase formation from the viewpoint of allowable polar interactions, and then we model these interactions as a function of terminal aliphatic chain length. By incorporating a functional group at the end of one, or both, of the aliphatic chains we study the effects caused by intermolecular interfacial interactions in lamellar phases, and in particular the formation of synclinic or anticlinic modifications. We then develop these ideas with respect to dimers, trimers, tetramers, etc. We show, for dendritic systems, that at a certain level of molecular complexity the local mesogenic interactions become irrelevant, and it is gross molecular shape that determines mesophase stability. The outcome of these studies is to link the complexity of the molecular interactions at the nanoscale level, which lead to the creation of the various liquid-crystalline polymorphs, with the formation of mesophases that are dependent on complex shape dependencies for mesoscopic supermolecular architectures.
  Ibrahim A. Radini and Michael Hird
  The synthesis and mesomorphic properties of a systematic range of ortho difluoroterphenyls with a bulky terminal chain are detailed. The bulky terminal chain consists of either a tertiarybutyl group or a trimethylsilyl unit, each separated from the core by a short (dimethylene) chain, with the other terminal chain being either octyloxy or heptyl. The synthesis of the materials was affected efficiently using a combination of low temperature lithiations and palladium-catalysed cross-coupling reactions. Unusually for liquid crystals with bulky terminal chains, the smectic phase stability (particularly smectic C) is upheld by more than the nematic phase stability, and in most cases the smectic C phase stability is actually higher than comparable analogues with conventional unbranched terminal chains. It is postulated that the surprisingly high smectic C phase stability results from a phase separation effect due to the incompatibility of the spherical bulky group and the conventional unbranched terminal chain, hence implying that the smectic 'layers' are well defined, and such definition of the layers bodes well for bookshelf geometry in ferroelectric mixtures.
  Michael Hird
  Molecular chirality confers the necessary reduced symmetry to tilted smectic liquid crystals and disordered crystals to generate ferroelectric properties. By definition, ferroelectrics are materials that possess a spontaneous polarisation in the absence of an external field, and on the application of an electric field, the polarisation can be reoriented. Combine the fluidity of liquid crystals with ferroelectric properties and a fast-switching electro-optic device is possible. However, the road was very rocky in developing ferroelectric technology into commercially viable devices, despite the many advantages over the existing nematic-based devices. Indeed, research and development is on-going to enable ferroelectric technology to be more widely adopted. This review introduces the phenomenon of ferroelectric liquid crystals and charts the development of the technology to commercially viable devices, with a specific focus on the development of suitable materials in terms of design, synthesis and properties.
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