Diffusion Anomaly in an Associating Lattice Gas Model

TL;DR

This paper explores how an associating lattice gas model exhibits diffusion anomalies linked to its liquid-liquid phase transition and density maxima, revealing complex thermodynamic and dynamic behaviors.

Contribution

It introduces a detailed analysis of diffusion anomalies in an ALG model, connecting them to phase transitions and density maxima, which is a novel insight.

Findings

Diffusion constant shows a maximum and minimum at specific densities.

Diffusivity extrema line is near the liquid-liquid critical point.

Anomalous diffusion behavior occurs within the TMD region.

Abstract

We investigate the relation between thermodynamic and dynamic properties of an associating lattice gas (ALG) model. The ALG combines a two dimensional lattice gas with particles interacting through a soft core potential and orientational degrees of freedom. From the competition between the directional attractive forces and the soft core potential results two liquid phases, double criticality and density anomaly. We study the mobility of the molecules in this model by calculating the diffusion constant at a constant temperature, $D$. We show that $D$ has a maximum at a density $\rho_{max}$ and a minimum at a density $\rho_{min}<\rho_{max}$. Between these densities the diffusivity differs from the one expected for normal liquids. We also show that in the pressure-temperature phase-diagram the line of extrema in diffusivity is close to the liquid-liquid critical point and it is inside the temperature of maximum density (TMD) line.