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06:44
From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Stability and metastability of bromine clathrate polymorphs
Andrew H Nguyen1, Valeria Molinero
1Department of Chemistry, The University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850, United States.
The Journal of Physical Chemistry. B
|May 4, 2013
Summary
This study used molecular dynamics simulations to investigate bromine hydrate crystal structures. Results show that metastable sI and sII bromine hydrates are plausible, with melting points close to the tetragonal structure.
Area of Science:
- Materials Science
- Physical Chemistry
- Computational Chemistry
Background:
- Clathrate hydrates are crystalline solids where water cages trap guest molecules.
- Two common clathrate hydrate structures are cubic sI and sII.
- Bromine hydrate is known to form a tetragonal structure (TS), but the stability of other polymorphs is debated.
Purpose of the Study:
- To investigate the thermodynamic stability of different bromine hydrate polymorphs (sI, sII, TS, HS-I).
- To develop a compatible coarse-grained model for bromine and water.
- To determine the relative stability and melting points of bromine hydrate polymorphs.
Main Methods:
- Utilized molecular dynamics simulations with the coarse-grained mW water model.
- Developed and parametrized a coarse-grained bromine model compatible with mW water.
- Calculated thermodynamic stability and predicted melting temperatures for various hydrate structures.
Main Results:
- The mW model accurately reproduced the relative energies of empty clathrate polymorphs and phase diagrams.
- A narrow parameter space exists where the tetragonal structure is marginally more stable than sI or sII.
- Predicted melting temperatures: TS (281 K), sII (279 K), and sI (276 K).
Conclusions:
- The predicted melting temperatures suggest that metastable sII and sI bromine hydrates can form.
- The study provides crucial data on the thermodynamic stability of bromine hydrate polymorphs.
- Coarse-grained simulations offer a viable approach for studying complex hydrate systems.
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