Estudo por ressonancia magnetic nuclear da ordem e dinamica molecular em mesofases esmeticas de dupla camada.

We present the proton Nuclear Magnetic Resonance (NMR) study of order and molecular dynamics in nematic phase, smectic bilayer A, C and C-anti clinic of the 4-octylphenyl 2-chloro-4-(4-cyano benzoyloxy) benzoate, DB_8C1 for short. The study of the molecular order in the tilt phases was based in the angular evolution of the second moment of the NMR spectra with the sample orientation in the magnetic field for 1.4 T and 2.1 T magnetic fields. The developed models allows the interpretation of the experimental results and the estimation of the tilt angle in all studied tilted smectic phases: C, C (anti clinic type), C * and C*A. The model used in the smectic C phase permits also to get the ratio between the elastic and magnetic components of the reorientation energy of the compound in the magnetic field. A comparative study of the molecular dynamics in all the DB_8C1 mesophases was performed. The proton spin-lattice relaxation rate was measured in a broad Larmor frequency range (300 Hz-300 MHz) using both conventional and Field Cycling NMR techniques. The experimental results interpretation was based in the magnetic relaxation mechanisms associated to the auto diffusion movement, rotations reorientation and collective movements. The low frequency relaxation for the Sm C and Sm C results from director fluctuations occurring without layer distortions, T1 v1/2 and layers undulations without T1 V"1. The self diffusion decrease between layers in the Sm C? verified in the experimental results interpretation agrees with the anti clinic structure of the mesophase.Available from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga