Antiferroelectric liquid crystals: Interplay of simplicity and complexity

This paper reviews nearly 20 years of research related to antiferroelectric liquid crystals and gives a short overview of possible applications. Antiferroelectric liquid crystals is the common name for smectic liquid crystals formed of chiral elongated molecules that exhibit a number of smectic (Sm) tilted structures with variation of the strong-tilt azimuthal direction from layer to layer (i.e., nonsynclinic structures). The phases have varying crystallographic unit periodicity from a few (SmC alpha*), four (SmCFI2*), three (SmCFI1*), and two (SmCA*) smectic layers and all of the phases possess liquid-lik e order inside the layer. The review describes the discovery of these phases and various methods used for their identification and to determine their structures and their properties. A theoretical description of these systems is also given; one of the models-the discrete phenomenological model-of antiferroelectric liquid crystals is discussed in detail as this model allows for an explanation of phase structures and observed phase sequences under changes of temperature or external fields that is most consistent with experimental results.