Molecular Dynamics of a ferroelectric smectogen in its Smectic phases by means of 2H NMR Spectroscopy

In this work the dynamic behaviour of the ferroelectric liquid crystal (-)-(S)-[4-(2-methylbutyloxycarbonyl) phenyl] 4-n-heptylbiphenylcarboxylate (MBHB) in its smectic A (SmA), unwound chiral smectic C (uSmC*) and chiral smectic C (SmC*) phases has been studied by means of H-2 NMR spectroscopy. Zeeman (T-1Z) and quadrupolar (T-1Q) spin-lattice relaxation times have been analysed to extract dynamic parameters ( diffusion coefficients and activation energies). The small step rotation diffusion model in the uniaxial approximation has been used to describe overall spinning and tumbling motions, and the strong collision model to describe the internal reorientations of the aromatic fragment. Relaxation data in the SmC* phase have been analysed by using a theoretical approach. The dynamic features obtained in the smectic phases of this mesogen are here presented and discussed in comparison with the results obtained in other ferroelectric liquid crystals, focusing on the fast regime of motions.