Phase behaviour of n-CB liquid crystals confined to controlled pore glasses

In this review, we present the phase behaviour of liquid crystals (LCs) confined to Controlled-Pore Glasses (CPG) of various pore sizes. We consider either non-treated or silane-treated CPG pore surfaces, which impose parallel and homeotropic alignment to n-cyanobiphenyl (n-CB) LCs, respectively. The resulting nematic or smectic ordering depends on the characteristic void radii R and is well described in terms of the Landau-de Gennes free energy. Experimental data for different n-CB LCs, 5CB, 8CB, and 12CB, demonstrate phase transitions in orientation and translational degrees of freedom. In the bulk, 5CB and 8CB exhibit on cooling from the isotropic (I) phase the 1st order isotropic-nematic (I−N) phase transitions. In addition, 8CB also exhibits on further cooling a 2nd order nematic-smectic A (N−SmA) phase transition. 12CB, on the other hand, only has a 1st order isotropic-smectic A (I−SmA) phase transition. The bulk LCs exhibit a variety of different phase structures. When LCs are confined to porous media, their phase structures can be modified and even glass transition is possible.