Influence Of Confinement On Molecular And Director Reorientational Dynamics Of Liquid Crystal

We present the qualitative results of investigations of influence of confinement of liquid crystal in random porous medium on relaxation due to molecular reorientations investigated by dielectric spectroscopy and fluctuations of director orientations (collective relaxation) investigated by photon correlation spectroscopy. The relaxation times of the process due to the molecular rotations in deeply supercooled state of confined liquid crystal were slower than at the temperatures corresponding to nematic phase by a factor of 10(6). This slowing down was accompanied by anomalous broadening of the dielectric spectra. We attribute this qualitative change in molecular relaxation to coupling of molecules to the pore walls and among themselves via molecule-wall interactions. In the nematic phase of bulk liquid crystals, the relaxation process due to director orientation fluctuations (collective mode) was single exponential. The dynamics of this process was also drastically modified by random confinement. The slow relaxation process, which does not exist in the bulk liquid crystal, and a broad spectrum of relaxation times, appear for confined liquid crystal. These results on the influence of confinement on relaxation properties of liquid crystal were complimented by differential scanning calorimetry experiments. (C) 2009 Elsevier B.V. All rights reserved.