Abstract
AbstractMultipulse dynamic NMR techniques have been employed to investigate collective motions and viscoelastic properties in a main chain liquid crystal polymer and low molar mass analogues in the nematic phase. Transverse deuteron spin relaxation times measured as a function of pulse spacing using a modified Carr‐Purcell‐Meiboom‐Gill pulse sequence are analysed in terms of a simple hydrodynamic model for nematic director fluctuations. Combining these results with those of NMR slow sample spinning experiments allows determination of the effective viscosity and the average elastic constant of the material. Results are compared for compounds with different molecular weights and with the results of analogous proton field‐cycling experiments. The viscosity is found to increase approximately as the square of the molecular weight, Mn, whilst the elastic constant shows a much shallower Mn dependence apparently tending to a plateau value at moderate molecular weights.
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