Ultra slow behavior of glass-forming liquids

Participants: Pedro Ezequiel Ramírez, Edilio Lázaro Lázaro, Magdaleno Medina Noyola, Patricia Mendoza

Ordinary materials can be classified into two broad categories: those who have reached their thermodynamic equilibrium state and those which have not. Thermodynamic equilibrium means that the system choose the state in which the entropy is a maximum. Materials in equilibrium have stationary properties, while the non-equilibrium materials evolve until they can achieve the equilibrium state. Different materials have different relaxation times and depends on several factors such as the molecular nature of the material, the process used to obtain the final state, restrictions, etc. However, sometimes the equilibration time can be very long, leaving the material in a non-equilibrium condition. This diverging condition of the relaxation time is known as dynamic arrest and is fundamental for the understanding of common materials like glass, in which the molecules should be accommodated in an orderly (crystalline) arrangement that is frustrated due to dynamic conditions, giving an amorphous solid. The dynamic arrest phenomenon occurs not only in the onset of glass transition but also on the dynamics of colloidal dispersions, frustrated magnets, granular packing, folding complex polymers (like proteins), among others. Although in everyday life we encounter many dynamically-arrested materials there are not a well stablished theory able to understand these materials, much less predict their properties or the conditions under which they form. Several members of our group have developed a first-principles theory, which is basically an extension of the irreversible thermodynamics of Onsager, to study the evolution of a thermodynamic system from its initial state to the final state. The first applications to systems of hard spheres distinguish the conditions under which the equilibration is possible in contrast with those in which the final state is arrested and some properties continue changing, a phenomenon known as aging. Our goal is understand the non-equilibrium phenomena in a deeply manner and use this theoretical framework on the description of out-of-equilibrium materials.

Last Uptade: January 2015