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The University of Southampton
Chemistry

Research project: Luckhurst: Thermotropic Biaxial Nematic Liquid Crystals

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The common nematic phase currently used in display applications has uniaxial symmetry. However, Marvin Freiser has shown, on the basis of molecular field calculations that, in addition to this uniaxial phase, there should also be a nematic phase with biaxial symmetry. This prediction has stimulated much interest in the discovery of this phase and not only because of its potential applications.

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Following the original prediction there has been an increasing number of claims to have found this phase. However, it has proved to be difficult to obtain unambiguous experimental evidence for the existence of the biaxial nematic. An exception to this problem is to use a methodology based on deuterium NMR spectroscopy. Here the partially averaged quadrupolar tensor is determined and the symmetry of its principal components is taken to reflect the symmetry of the phase. We have used this approach to demonstrate that many of the compounds claimed to form biaxial nematics do in fact from just uniaxial nematic phases. We are developing this methodology further to facilitate the measurement of the principal components of the quadrupolar tensor both for deuteriated mesogens and for deuteriated probe molecules.

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In addition to our experimental studies of compounds thought to form a biaxial nematic we are also engaged in theoretical and simulation studies of the phase. These help, in part, to establish benchmarks against which the experimental results can be judged. It is also to be expected that the predictions of theory and the results of simulation will be valuable as a guide to the creation of real mesogens capable of forming the elusive biaxial nematic phase. Of singular importance is the development of models which include the intrinsic flexibility of the constituent molecules. This is a challenging but essential task because most mesogenic molecules are non-rigid and the biaxiality of the conformers can be significant.

 

Related research groups

Computational Systems Chemistry
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