Proton Multiple Quantum NMR Studies of Space and End Chain Conformation in Liquid Crystals

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The problem of the conformation and ordering of flexible chains in anisotropic phases has attracted a good deal of attention in recent years. The motivation of most of this work is a desire to understand the manner in which alkyl chains pendant to aromatic cores influence mesomorphic phase properties and stability. Liquid crystal polymers have also been the subject of research as possible sources of high tensile strength fibers and coatings, and for their possible applications in electro-optic devices. Although polymers with rigid backbones do not generally form liquid crystalline phases, or decompose before melting into memorphic phases, the introduction of flexible spacer chains into the polymer backbone will lower mesophase transition temperatures to below the range of thermal decomposition. Deuterium NMR spectroscopy has been the principal tool for probing the microscopic structure and dynamics of end and spacer chains, and for testing models of chain ordering in nematic phases. Professor Drobny proposes an approach to studying spacer and end chain ordering in the nematic phase and in several in low temperature mesophases using multiple quantum spectroscopy. Rather than test models of chain ordering and conformation, conformational probabilities and order tensor elements will be directly calculated from proton-proton and proton-carbon dipolar couplings obtained from multiple quantum spectra.