Microscopic to macroscopic modelling in liquid crystals

Much work has been dedicated to relating the phenomenological Landau-de Gennes model for liquid crystalline materials to its simpler large-domain limit, the Oseen-Frank model. As Landau-de Gennes is, however, phenomenological, it begs the question as to whether Oseen-Frank may be justi ed from models with a more sound physical justi cation. In this talk we outline some recent work on obtaining Oseen-Frank, for both nematic and cholesteric liquid crystals, as a large-domain limit of a more fundamental mean- eld model, where material constants appearing in the limiting gradient-type energy can be derived from more fundamental pairwise interactions of molecules.