Thermal conductivity of supercooled water

Area of Science:

• Thermodynamics
• Physical Chemistry
• Soft Matter Physics

Background:

• Supercooled water displays unusual thermodynamic properties, including increasing heat capacity and decreasing thermal diffusivity as temperature drops.
• These anomalies are potentially linked to a hypothesized liquid-liquid critical point (LLCP) in water.
• Unlike the vapor-liquid critical point, thermal conductivity in supercooled water does not show expected divergence due to critical fluctuations.

Purpose of the Study:

• To investigate the effect of critical fluctuations on the thermal conductivity of supercooled water using mode-coupling theory.
• To reconcile the observed thermal conductivity behavior with the thermodynamic anomalies and the hypothesized LLCP.
• To understand the differences in thermal conductivity behavior between vapor-liquid and liquid-liquid critical points in water.

Main Methods:

• Experimental measurements of heat capacity and thermal diffusivity of supercooled water down to -37°C.
• Application of mode-coupling theory to model critical fluctuations and their impact on thermal conductivity.
• Calculation of thermal conductivity as the product of thermal diffusivity and heat capacity.

Main Results:

• Anomalous increase in heat capacity and decrease in thermal diffusivity were confirmed in supercooled water.
• Mode-coupling theory predicted that critical fluctuation enhancement of thermal conductivity is too small to be experimentally detected.
• Thermal conductivity behavior, including a minimum upon cooling, is explained by the observed thermodynamic anomalies.

Conclusions:

• The lack of measurable anomaly in thermal conductivity is consistent with theoretical predictions for supercooled water near its hypothesized LLCP.
• The observed minimum in thermal conductivity can be attributed to the interplay of anomalous heat capacity and thermal diffusivity.
• Significant differences exist in thermal conductivity scaling between vapor-liquid and liquid-liquid critical points in water.