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The polymorphism of 4-cyano-4 0 -pentylbiphenyl (5CB) was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction, and proton nuclear magnetic resonance (NMR) experiments. Three new phases has been identified and characterized structurally and dynamically. By a slow cooling at a rate 0.2 K/min, the nematic phase crystallizes into a phase noted C1. Upon a fastest cooling ( ! 5 K/min) a glassy liquid crystal (GLC) phase with a glass transition temperature T g ¼ 208 K, is formed. Upon heating up both the solid state C1 and the GLC phase, a second crystalline phase C2 (DH ¼ 49 J/g.K) which is more stable than C1 (DH ¼ 36 J/g.K) can be obtained. The proposed phase diagram has been investigated by proton NMR lineshape analysis. The motional correlation time of end-chain methyl group motion was determined by means of spin-lattice relaxation time (T 1 ) analysis.

The behaviour of freely suspended smectic-C* ( SmC(*)) films at the bulk SmC(*)-cholesteric ( N(*)) phase transition has been investigated using polarized-reflected-light microscopy. Our experimental observations show that above the bulk SmC(*)- N(*) phase transition the N(*) order appears in different ways according to the film thickness. In thin films, the conventional layer-by-layer thinning occurs. In films of intermediate thickness N(*) inclusions nucleate inside the SmC(*) film. The distortions of the in-plane orientational order of the SmC(*) host phase induce elastic interactions between the inclusions and lead to their self-organization in chain-like structures. Both the dynamic of the chaining and the parameters driving the equilibrium distance between the inclusions in the chain are investigated. In thick films, N(*) fingers grow inside the film. The influence of the experimental conditions on the various processes is analysed.

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A discrete phenomenological model of antiferroelectric liquid crystals is used to study the structures and phase transitions in bulk samples and thin films. An important ingredient of our investigations is minimization of the free energy with respect to the phase and modulus of the order parameter. A simple version of the free energy, which contains only the nearest-neighbor and the next-nearest-neighbor layer interactions gives a complete phase diagram with all the observed smectic-C* (SmC*) variant phases. In thin free-standing films, surface ordering may lead to suppression of the bulk SmC(*)(alpha) helix and to formation of planar structures. Transitions between these structures are accompanied by the 90 degrees reorientation of the polarization direction. We also discuss the influence of chirality on subphase structures.