Relaxation columnar discotics

The apparent disagreement between simulation results and experimental observations on the the existence of power law relaxation near the isotropic-columnar (I-C) phase boundary needs further attention. This appears to be associated with the existence of nematic-like fluctuations in the experimental system. This can be checked, on the experimental side, by studying the relaxation near the I-C phase boundary located away from the discotic-nematic phase. For simulation, a careful analysis should be done by changing the temperature and density along the phase coexistence line and studying the existence or lack of nematic-like orientational fluctuations. 

R 553 A. C. Ribeiro, P. J. Sebastiao and C. Cruz, Contribution of Proton NMR Relaxation to the Investigation of Molecular Dynamics in Columnar Mesophases of Discotic and Polycatenar Molecules , Pramana, 2003,61, 205... 

Dynamic processes that can be investigated by NMR include both the motions of individual molecules, e.g., conformational dynamics and molecular rotations, and collective motions, e.g., director fluctuations in nematic systems, layer undulations in smectic systems, or density modulations in columnar phases of discotic systems. Self-diffusion can be measured by NMR relaxation or field gradient methods, as discussed in Sec. 13 of Chap. VII of this Volume. Table 1 gives an overview of the time scales accessible by the most common experimental techniques and examples of the type of motion that can be studied. 

In low molar mass liquid crystals, conformational dynamics is typically too fast to be studied by 2D exchange NMR or line shape analysis. Dynamical studies of small molecules belong therefore almost exclusively to the realm of relaxation experiments. There are, however, cases of slow motions even in low molar mass systems, which can be investigated by 2D exchange spectroscopy. A recently investigated example is a discotic tetrabenzocyclophane derivative, which shows very slow motions in the columnar phase compared to other discotic compounds [97]. As illustrated in Fig. 6, deute-... 

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