Non-conventional liquid crystals - the importance of micro-segregation for self-organisation

Selected examples of recently synthesised non-conventional liquid crystals are highlighted. These are cyclic and open chain oligoamides, molecules containing tetrahedral or octahedral central cores, dendrimers, polyhydroxy amphiphiles, taper shaped molecules, liquid crystals with perfluorinated or oligosiloxane segments, rod-coil molecules as well as special types of polycatenar and laterally branched calamitic molecules. Their mesomorphic properties are discussed as a consequence of incompatibility, micro-segregation and space filling. The analysis is based on the general concept of amphiphilicity, which describes any chemical or structural contrast within a molecule, such as hydrophilic/lipophilic, polar/non-polar, hydrocarbon/fluorocarbon, oligosiloxane/hydrocarbon or rigid/flexible. These non-conventional liquid crystals will be regarded as block molecules. Depending on the degree of chemical and structural difference and the size of the different building blocks micro-segregation can occur with formation of lamellar, columnar or spheroidal aggregates which organise to smectic, columnar and cubic mesophases. The striking analogies between the polymorphism of thermotropic and lyotropic liquid crystals and block-copolymers are pointed out.