"The structure of ordinary liquids is altered near a solid surface. The symmetry breaking leads to positional and orientational ordering of molecules. The ordering effect extends generally up to a few molecular dimensions only. A solid interface also plays a well-documented role on the nucleation and growth of crystals. But probably the richer physical situations are observed in the case of liquid crystals, notably anchoring and orientational wetting effects. Liquid crystals are ideal systems to study surface effects for many reasons. First, their fluid character allows reaching thermodynamic equilibrium easily. Second, surface-induced orientational and positional ordering effects can be selectively studied. Third, liquid crystals display several phase transitions around which peculiar phenomena occur. Fourth, liquid crystalline phases are highly symmetrical and allow an easy structural characterization by powder X-ray diffraction. Fifth, liquid crystalline compounds are generally more soluble and easier to process into thin films than crystals. In case of discotic liquid crystals, unusual and interesting phases appear in the vicinity of solid substrates. Such “thin film” phase differs from those for crystalline compounds, where surface induced polymorphism occurs. Such thin film phases in crystals are thermodynamically unstable since a perturbation of the system leads to its transformation into a more stable polymorph that exists also in bulk. The substrate-induced phases observed in discotic liquid crystals are more ordered than the bulk ones and exhibit a three-dimensional order whereas the bulk ones are liquid crystalline and have a two-dimensional order. This project aims to gain a fundamental understanding of the physical and chemical parameters that governs the formation of substrate-induced phases in discotic liquid crystals through a combined theoretical and experimental approach."
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