The molecular dynamics of 4-octyl-4'-cyanobiphenyl and 4-pentyl-4'-cyanobip
henyl, confined to the mesopores with diameters less than 25 Angstrom of th
e molecular sieve AlMCN-41, was investigated over a wide temperature range
using broadband dielectric spectroscopy. As expected, the phase transitions
of the bulk liquid crystals cannot be detected for the confined molecules.
A new, slow relaxational process occurs over the whole temperature range d
ue to the motions of the molecules confined in the pores; the temperature d
ependence of the characteristic frequency obeys a Vogel-Fulcher-Tamman (VFT
) law associated with a glassy state. The orientational order within these
small pores is mostly dominated by the local environment. (C) 1999 Elsevier
Science B.V. All rights reserved.