Abstract

Two-dimensional Fourier transform (2D-FT) and CW-ESR experiments at X-band frequencies were performed over a broad range of temperatures covering the solid and melt states of a liquid crystalline (LC) polymer. The CW-ESR experiments were analyzed by conventional motional models. The nematic phase was macroscopically aligned in the dc magnetic field, whereas the solid state showed microscopic order but macroscopic disorder (MOMD). An end-label on the polymer showed smaller ordering and larger reorientational rates than that of the cholestane (CSL) spin probe dissolved in the same polymer, since the former can reorient by local internal chain modes. It was demonstrated that the 2D-FT-ESR experiments provide greatly enhanced resolution to the ordering and dynamics of the end-label, especially when performed as 2D-ELDOR (electron−electron double resonance) experiments as a function of mixing time. The conventional model of Brownian reorientation in an orienting potential was unsuccessful in interpreting these...

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