Thermodynamics and collective modes in hydrogen-bonded fluids

Area of Science:

• Thermodynamics
• Fluid Dynamics
• Condensed Matter Physics

Background:

• General theories for liquid and supercritical fluid thermodynamics are lacking, unlike for crystalline solids.
• Extending solid-state concepts like phonons and configurational entropy to liquids is challenging, especially for anomalous liquids like water.
• Supercritical fluids are vital in energy and environmental applications but their properties remain poorly understood.

Purpose of the Study:

• To develop a theoretical framework for understanding the thermodynamics of simple fluids across liquid, supercritical, and gaseous states.
• To identify a key parameter from the phonon spectrum that governs fluid thermodynamics.
• To differentiate the thermodynamic behavior of simple fluids from hydrogen-bonded fluids.

Main Methods:

• Utilizing the spectrum of propagating phonons to define fluid thermodynamics.
• Deriving a single parameter from the phonon spectrum to determine non-ideal entropy.
• Relating phonon theory to excess entropy scaling and corresponding states in fluids.

Main Results:

• A single parameter from the phonon spectrum successfully describes the thermodynamics of simple fluids across phase transitions.
• A clear distinction is established between simple fluids and hydrogen-bonded fluids based on their thermodynamic behavior.
• Phonon thermodynamics explains corresponding states across the fluid phase diagram and relates to excess entropy scaling.

Conclusions:

• Phonon thermodynamics provides a unifying theoretical framework for simple fluids, including supercritical states.
• The study highlights the limitations of phonon spectrum analysis for hydrogen-bonded fluids.
• These findings offer crucial theoretical insights into supercritical fluids, aiding their application in environmental and energy technologies.