Surface-induced order and diffusion in 5CB liquid crystal confined to porous glass

Liquid crystals confined into small cavities art: known to have a weak orie ntational order even above the nematic-isotropic transition temperature. Th e surface-induced order and molecular dynamics in this temperature range ar e studied with the aid of deuteron NMR spectra, spin relaxation times T-1 a nd T-2. proton dipolar-correlation effect, and direct measurements of the e ffective diffusion coefficient for the liquid crystal 5CB confined to contr olled-pore glasses. Our results show that an arrangement of molecules paral lel to the wall is induced by local molecular interactions between the liqu id crystal and solid, resulting in a weak and temperature independent surfa ce order parameter, S-0 similar to 0.02 +/- 0.01. There is no indication of a significant slowing-down of molecular diffusion at the wall, neither rot ational nor translational. In cavities of nanometer size, where the nematic order evolves gradually upon cooling, a broadening of the NMR linewidths d ue to dynamic effects should be taken into account. (C) 2001 Elsevier Scien ce Inc. All rights reserved.