05. Rotational dynamics and orientational order of compounds with glassy phases

Nirvana Caballero

2016

The glassy state has been known and used since ancestral times; nowadays glasses are materials of paramount technological importance. However, from the physical point of view, the glass phenomenology is far from being well understood. In particular, the glassy dynamics of rigid molecules is still controversial: the physics behind the relaxation processes known as Johari-Goldstein relaxations, were the time scales are longer than the ruled by viscosity is still unknown. With the main objective of understanding the mechanisms involved in relaxations, in this thesis, real systems with low degree of complexity were studied. Compounds of the form XYnZ4−n were chosen. In particular, the systems of rigid molecules CBrnCl4−n n=0,1 were studied. These compounds exhibit a series of thermally induced solid-solid phase transitions that are attributed to the ability to thermally activate rotational degrees of freedom within the crystalline state. With the aim of studying the role of geometry on materials of the form CYCl3, the compounds with Y=H,Cl and Br were studied and compared.