Controlling disorder in liquid crystal aerosil dispersions

The effect of disorder in the behavior of liquid crystal (LC) is assessed and controlled by dispersing known amounts of silica aerosil in the liquid crystal material. Using deuteron nuclear magnetic resonance, the director configuration and the orientational order was determined for hydrophilic aerosil dispersions in octylcyanobiphenyl. The confined liquid crystal exhibits a well-defined alignment as the silica spheres stabilize the molecular configuration. At low silica densities, a silica network is eventually established, forming a soft gel. When the sample orientation in the magnetic field is changed, a few silica strands links are broken and a fraction of the LC molecules is realigned. The field anneals the random disorder introduced by the aerosil up to a certain density beyond which, in the so-called stiff-gel regime, disordering effects completely dominate. At a fixed temperature in the isotropic phase, there is surface-induced order that is linearly proportional to the silica density.