Molecular Dynamics in the Smectic A and C Phases in a Long-Chain Ferroelectric Liquid Crystal:~2H NMR,Dielectric Properties,and a Theoretical Treatment

摘要

In this work,the rotational-diffusion coefficients D_(||) and D_(perpendicular) for the ferroelectric smectogen (+)-(S)-4-[4'-(1-methylheptyloxy)] biphenyl 4-(10-undecenyloxy)benzoate have been studied by means of ~2H NMR spectroscopy in the smectic C phase,using a new theoretical approach (Domenici,V.;Geppi,M.;Veracini,C.A.Chem.Phys.Lett.2003,382,518).The analysis of spin-lattice relaxation times has been performed in terms of the diffusional constant and the activation energy of the internal and overall molecular-reorientational motions,and the results are compared to the smectic A (SmA) phase.Moreover,from the ~2H NMR data in the SmA phase,the dielectric permittivity and the dielectric relaxation time functions tau_(mn)~L are investigated using a theoretical approach.The longitudinal and transverse components of the real RCHI_(gamma)(omega) and imaginary CHI_(gamma)(omega)(gamma=||,perpendicular) parts of the complex susceptibility tensor and the nematic-like rotational-viscosity coefficients,lambda_2 and lambda_5,are calculated.