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Coupling between structural relaxation and diffusion in glass-forming liquids under pressure variation
Anh D Phan1, Kajetan Koperwas, Marian Paluch
1Faculty of Materials Science and Engineering, Phenikaa Institute for Advanced Study, Phenikaa University, Hanoi 12116, Vietnam. anh.phanduc@phenikaa-uni.edu.vn.
Physical Chemistry Chemical Physics : PCCP
|October 21, 2020
Summary
High pressure affects glass-forming liquids by slowing molecular motion. Elastically Collective Nonlinear Langevin Equation (ECNLE) theory and molecular dynamics (MD) simulations reveal a pressure-independent coupling between structural relaxation and diffusion.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Physical Chemistry
Background:
- Glass-forming liquids exhibit complex dynamics related to structural relaxation and diffusion.
- Understanding the influence of external pressure on these dynamics is crucial for materials design and fundamental physics.
Purpose of the Study:
- To investigate the effects of external pressure on structural relaxation and activated diffusion in glass-forming liquids.
- To compare theoretical predictions from Elastically Collective Nonlinear Langevin Equation (ECNLE) theory with molecular dynamics (MD) simulations.
Main Methods:
- Utilized Elastically Collective Nonlinear Langevin Equation (ECNLE) theory.
- Performed molecular dynamics (MD) simulations.
- Analyzed structural relaxation times and diffusion constants under varying pressures.
Main Results:
- External pressure restricts molecular motion, slowing cooperative mobility and increasing glass transition temperature and dynamic fragility.
- MD simulations showed a decrease in fragility above 1000 bar, diverging from ECNLE predictions.
- A linear coupling between structural relaxation time and inverse diffusion constant was observed, independent of pressure.
Conclusions:
- ECNLE theory and MD simulations provide complementary insights into pressure-dependent dynamics of glass-forming liquids.
- The pressure-independent coupling offers a fundamental relationship governing liquid dynamics.
- Discrepancies at high pressures highlight areas for further theoretical refinement.
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