The role of calorimetry in the structural study of mesophases and their glass states

Four mesomorphic states of matter are known: liquid crystal, plastic crystal, condis phase, and rotator phase, all of them are solid phases, except liquid crystal, which is fluid. Plastic crystal (also called ODIC, orientational disordered crystal), rotator phase, and even condis phase have been considered the same phase by many authors. Differences between them will be established to define their own characteristics. Two organic salts series have been used for discussion in this presentation: (1) thallium(I) alkanoate series, that presents a condis mesophase, and (2) lead(II) alkanoate series, that present a rotator one, both forming a smectic A-like liquid crystal phase. Based in the literature data of the alkyl ammonium bromide series it can be established that the short chain length members would present a rotator phase, and, the large chain ones, a condis phase. Five different glass states are known (four with partial crystalline order), corresponding with the above mentioned mesophases, and the ordinary (amorphous) glass state.