Reentrant Phase Transitions in Liquid Crystals

Phenomenon of reentrancy of a low symmetry (high order) phase in-between two high symmetry (low order) phases as the transition thermodynamic parameter (e.g., temperature or pressure or concentration) and/or applied field are crossed is known as “reentrant phase transition (RPT)”. This phenomenon is intrinsically novel and has been observe3d in amazingly diverse systems. Based on the mere entropy-energetic arguments the appearance of reentrant phase (or phases) is inexplicable. The present chapter 5 presents a comprehensive summary of the developments of last three decades in the area of RPT in liquid crystals. Various aspects of observed reentrant phases in mesogens composed of achiral calamitic, chiral calamitic, disc-shaped, and bent-core molecules are discussed in details.The microscopic origin of the RPT varies from system to system and is an open problem.