Structural relaxation in liquid water by inelastic UV scattering

Area of Science:

• Condensed matter physics
• Physical chemistry
• Materials science

Background:

• Understanding the dynamics of supercooled water is crucial for various scientific fields.
• Previous studies have explored water's behavior in different states, but direct observation of structural relaxation in the supercooled region remains challenging.

Purpose of the Study:

• To investigate the dynamic structure factor of normal and supercooled liquid water.
• To observe and characterize the structural (alpha) relaxation in supercooled water.
• To experimentally validate predictions of mode-coupling theory for water dynamics.

Main Methods:

• Utilized a novel synchrotron radiation based inelastic ultraviolet scattering technique.
• Measured the dynamic structure factor at a momentum transfer Q of approximately 0.1 nm(-1).
• Covered a temperature range from 260 K to 340 K, encompassing both normal and supercooled states.

Main Results:

• Observed structural (alpha) relaxation in the supercooled temperature region (T ≤ 273 K).
• Found that the inverse relaxation time matches the frequency of probed sound modes.
• Determined a diverging behavior of relaxation time with a critical temperature (T_c) of approximately 220 K.

Conclusions:

• The experimental findings provide direct evidence of structural relaxation in supercooled water.
• The observed temperature dependence of relaxation time supports the predictions of mode-coupling theory.
• This study offers a unique experimental framework for understanding water dynamics near its glass transition.