Ordering and disordering effects in confined liquid crystals

Confined liquid crystals exhibit significantly different physical properties from those of a bulk. The confinement could have either ordering or disordering effects on a liquid crystal (LC) phase depending on the topology of the confining surface and on the surface-LC interaction. This dissertation presents a deuteron nuclear magnetic resonance (DNMR) study of confined nCB liquid crystals, focusing on the surface ordering effects of the Anopore membrane and the random disordering effects of the silica aerosil.; Anopore membranes are ideal hosts for the study of surface ordering effects because they have a large surface to volume ratio, and submicron cylindrical cavities that can easily be treated with a variety of surfactants. For smectogenic LCs 10CB and 12CB in surfactant treated Anopore, DNMR spectra reveal the existence of a translationally ordered pre-smectic layer at the cavity wall at a few degrees above the smectic-A-isotropic (A-I) transition. At higher temperatures the surface layer is of pre-nematic nature with weak orientational order. The transition from pre-nematic to pre-smectic can be either continuous or discontinuous depending on the surfactant, the surface coverage of the surfactant, and on the LC material used.; In Anopore, the director configuration of nCB is usually a parallel axial for planar anchoring conditions, and a planar-polar (planar-radial) in the nematic (smectic-A) phase for homeotropic anchoring conditions. In untreated Anopore cavities, DNMR spectra reveal an axial to radial structural transition as the chain length of nCB LC increases from n = 8 to 10, indicating a planar to homeotropic anchoring transition at the cavity wall. The director configuration of 10CB and 12CB, with weak homeotropic surface anchoring, depends strongly on the thermal history of the sample, the pore radius, and the atmosphere in the NMR tube.; Controllable amount of random quenched disorder can be introduced by dispersing nano-size aerosil particles into a liquid crystal. The aerosil particles can hydrogen bond together into fractal networks (gels), and distort the local LC directors by anchoring LC molecules at their spherical surfaces. Depending on the aerosil density, the liquid crystal-aerosil dispersions can be divided into three regimes: no-gel regime with minimal disorder; soft-gel regime with medium disorder and smeared phase transitions; and stiff-gel regime with fully quenched disorder and suppressed phase transitions. Hydrophobic aerosils induce weaker random disorder than hydrophilic ones with the same aerosil density. Inside the NMR magnetic field, most of the random aerosil gels can be annealed into anisotropic ones, except those with highest aerosil densities.