Bipolar configuration, nematics

Figure 12.7. Two configurations of lowest energy on a nematic disk with strong tangential anchoring at the boundary (a) bipolar with two n = defects and (b) monopolar with an n = 1 defect. Because the defects appear at the surface they could have also been given double strengths n, as discussed above (from [14]).

Figure 16. Bipolar (a) and radial (b) configuration of the nematic molecular directors in polymer dispersed nematic microdroplets [2021.

NMR, and particularly deuterium NMR, are the best experimental techniques for the determination of the director field and the molecular dynamics in submicron nematic droplets. The theoretical static proton NMR spectra of the nematic micro-droplets for a bipolar and a radial configuration are shown in Fig. 17 a. The corresponding motionally averaged spectra are shown in Fig. 17 b. Here the motional averaging is produced by translational diffusion which induces slow molecular rotations due to the non-uniform orientational ordering in the droplet [206]. 

The first study of the frequency and temperature dependence of the proton-spin lattice relaxation rate of micro-confined nematics has been reported by Vilfan et al. [202] for E7 nematic micro-droplets dispersed in an epoxy polymer. Here the bipolar molecular director configuration is expected and should be bigger then the radius of the droplets R. Instead of a doublet... 

Figure 17. (a) Simulated static proton NMR spectra of nematic microdroplets for the bipolar (NqIIHo) radial configurations, (b) Dynamic proton NMR spectra for (1) the bipolar (No /lo) and (2) the radial director configurations [206]. For = 50 the diffusion is slow whereas for e = 0.05 the diffusion is fast. Here e =A r lD with 2A being the static line splitting. 

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