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Liquid polymorphism and density anomaly in a lattice gas model
Vera B Henriques1, Marcia C Barbosa
1Instituto de Física, Universidade de Sao Paulo, Brazil. barbosa@if.ufrgs.br
Summary
This study models associating liquids, connecting polymorphism and density anomalies. The findings reveal a positive slope for the liquid coexistence line, challenging assumptions about liquid entropy and density anomalies.
Area of Science:
- Thermodynamics
- Statistical Mechanics
- Soft Matter Physics
Background:
- Associating liquids exhibit complex phase behavior, including polymorphism and density anomalies.
- Understanding the interplay between molecular interactions and macroscopic properties is crucial in soft matter physics.
Purpose of the Study:
- To develop a simple model connecting polymorphism and density anomalies in associating liquids.
- To investigate the phase diagram and liquid coexistence properties.
Main Methods:
- A two-dimensional lattice gas model with soft core interactions.
- Inclusion of orientational degrees of freedom using thermal 'ice variables'.
Main Results:
- The model predicts a phase diagram with two liquid phases and a density anomaly.
- The coexistence curve between low-density and high-density liquids shows a positive slope.
- This positive slope contradicts the hypothesis that high-density liquids are always more entropic.
Conclusions:
- Directional attractive forces competing with soft core potentials drive the observed phenomena.
- Density anomalies in associating liquids do not necessarily imply higher entropy in the high-density phase.
- The model provides a framework for understanding complex liquid behavior.