A field-cycling NMR study of nematic 4-pentyl-4 '-cyanobiphenyl confined in porous glasses

The proton spin-lattice relaxation time T-1 in the nematic liquid crystal 4 -pentyl-4'-cyanobiphenyl confined in a glassy porous matrix has been measur ed in a wide Larmor frequency range of 1 . 10(2)-2 . 10(7) Hz employing the fast field-cycling NMR technique. A strong influence of the restricted geo metry on the character of the T-1 dispersion was found. Our investigation c learly demonstrates the importance of the translationally induced molecular reorientations in inhomogeneous director field for the relaxation in the s amples with 200 and 80 nm mean pore size. The experimental results are in a good agreement with the theoretical predictions. In the sample with 7 nm p ore size the main contribution to the relaxation is ascribed to the slowing down of the molecular motion in the near-surface layer. Zero-field H-1 NMR spectra of a microconfined liquid crystal are reported for the first time.