Capturing Hydrate Formation Processes in Tetrahydrofuran/Water Mixtures with Temperature Resolved In Situ Synchrotron...

Area of Science:

• Materials Science
• Physical Chemistry
• Crystallography

Background:

• Clathrate hydrate formation mechanisms are crucial for both practical applications and fundamental scientific understanding.
• Investigating the low-temperature behavior of clathrate hydrates provides insights into molecular ordering and phase transitions.

Purpose of the Study:

• To elucidate the atomic-level molecular rearrangements during the formation of tetrahydrofuran (THF)-water clathrate hydrates.
• To characterize the structural evolution of THF-water mixtures under cryogenic conditions and controlled heating.

Main Methods:

• In situ synchrotron X-ray diffraction (XRD) and infrared (IR) spectroscopy were employed.
• Experiments utilized cryogenically deposited THF-water mixtures with slightly deuterated water in ultrahigh vacuum.
• In situ analysis allowed monitoring of local and long-range order evolution during temperature changes.

Main Results:

• An as-deposited THF-water sample exhibited a disordered diffraction pattern.
• Upon heating, THF segregated and crystallized, while water remained amorphous until 110 K.
• Crystalline THF melted and subsequently formed a type II clathrate hydrate with water, free from ice contamination, at higher temperatures.

Conclusions:

• The study provides detailed atomic-level insights into the molecular dynamics and structural transformations during clathrate hydrate formation.
• Distinct temperature-dependent structural changes were observed, culminating in the formation of a specific clathrate structure.
• Significant molecular mobility was highlighted even at low temperatures, influencing the hydrate formation pathway.