Pore-collapse in amorphous solid water: A dynamics study

Area of Science:

• Materials Science
• Physical Chemistry
• Condensed Matter Physics

Background:

• Vapor-deposited amorphous ice (amorphous solid water) undergoes structural changes upon heating.
• Micropore collapse and glass transition are key transformations occurring within specific temperature ranges.

Purpose of the Study:

• To differentiate and study the dynamics of micropore collapse and glass transition in amorphous solid water.
• To investigate the interplay between micropore collapse and glass transition during heating cycles.

Main Methods:

• Small-angle X-ray scattering (SAXS) to monitor micropore collapse.
• X-ray photon correlation spectroscopy (XPCS) to study combined dynamics.
• Heating and cooling cycles of amorphous solid water samples.

Main Results:

• Micropore collapse occurs between 100-145 K, with glass transition above 120 K.
• Heating a second time shows pore collapse only near the glass transition temperature (Tg).
• Both diffusive and ballistic processes contribute to pore collapse dynamics, with accelerated rates when collapse and transition co-occur.

Conclusions:

• Micropore collapse and glass transition are coupled processes that influence each other's dynamics.
• The glass transition in amorphous solid water is characterized by slow diffusive motion.
• Observed dynamics align with previous studies on amorphous solid water in different forms.