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Register a new userGlass transition as a decoupling-coupling mechanism of rotations
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Diaz-Sanchez Anastasio
Publication date
2002
fields
Physics
and research's language is
English
Authors
Anastasio Diaz-Sanchez
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We introduce a three-dimensional lattice gas model to study the glass transition. In this model the interactions come from the excluded volume and particles have five arms with an asymmetrical shape, which results in geometric frustration that inhibits full packing. Each particle has two degrees of freedom, the position and the orientation of the particle. We find a second order phase transition at a density $rhoapprox 0.305$, this transition decouples the orientation of the particles which can rotate without interaction in this degree of freedom until $rho=0.5$ is reached. Both the inverse diffusivity and the relaxation time follow a power law behavior for densities $rhole 0.5$. The crystallization at $rho=0.5$ is avoided because frustration lets to the system to reach higher densities, then the divergencies are overcome. For $rho > 0.5 $ the orientations of the particles are coupled and the dynamics is governed by both degrees of freedom.
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Topological defects are typically quantified relative to ordered backgrounds. The importance of these defects to the understanding of physical phenomena including diverse equilibrium melting transitions from low temperature ordered to higher temperatures disordered systems (and vice versa) can hardly be overstated. Amorphous materials such as glasses seem to constitute a fundamental challenge to this paradigm. A long held dogma is that transitions into and out of an amorphous glassy state are distinctly different from typical equilibrium phase transitions and must call for radically different concepts. In this work, we critique this belief. We examine systems that may be viewed as simultaneous distribution of different ordinary equilibrium structures. In particular, we focus on the analogs of melting (or freezing) transitions in such distributed systems. The theory that we arrive at yields dynamical, structural, and thermodynamic behaviors of glasses and supercooled fluids that, for the properties tested thus far, are in qualitative and quantitative agreement with experiment. We arrive at a prediction for the viscosity and dielectric relaxations that is universally satisfied for all experimentally measured supercooled liquids and glasses over 15 decades.
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