Solid-State 2-D NMR Correlation of Structure and Motion in Polymer Dispersed Liquid Crystals

Abstract

Abstract Two-dimensional Nuclear Magnetic Resonance (NMR) spectroscopy is used to characterize polymer dispersed liquid crystals (PDLCs) in the solid-state. The wideline separation (WISE) pulse sequence is used to correlate structure and mobility in a PDLC. The PDLC is 40% E7 as 0.4 μ droplets in an Epon 828 matrix. The WISE pulse sequence generates 1H wideline spectra in one dimension for each high resolution solid state 13C resonance in the other dimension. For each 13C resonance, the width of the 1H line shape reflects the mobility of the protons in the vicinity of the respective 13C. Spin diffusion is incorporated into the WISE pulse sequence to determine the relative spatial positions of components with different mobilities. The aliphatic portions of E7 exhibit extremely narrow 1H line widths of a few hundred hertz. Therefore, the aliphatic pendant groups of E7 undergo pseudo-random isotropic motions with rates above 1 MHz. The aromatic portions of E7 exhibit pronounced spinning sidebands in the 1H dimension. Therefore, the aromatic core of E7 undergoes anisotropic motions; specifically, ring flipping of the phenyl rings about their para axes. This ring flipping also occurs with rates exceeding 1 MHz.