CHAPTER 16: Stability of Real Liquid Crystals

This brief review summarizes and discusses the origin of the stability of molecular liquid crystals, bearing in mind the fundamental view that they appear as mesophases between ordered crystals and (completely disordered) isotropic liquids. The emphasis lies in the thermodynamic understanding that the relative position of the Gibbs energies determines stability. After briefly reviewing theoretical and computational scenarios of liquid crystal formation, some real liquid crystals are examined, paying attention to discrepancies between theoretical (computational) predictions. The comparison reveals a vital role of flexible alkyl chains present in real mesogenic molecules. Since most theoretical and computational studies have ignored such molecular details, it is concluded that the existing theoretical framework has been useful for a basic understanding but is a kind of “fantasy” applicable only for colloidal systems. This review should also be valuable for understanding ionic liquids, the practical definition of which involves their melting points determined by comparing the Gibbs energies of the crystal and the liquid.