Water Activity Measurement Using Shortwave Infrared (SWIR) Spectroscopy

Area of Science:

• Spectroscopy
• Physical Chemistry
• Materials Science

Background:

• Water activity (Aw) is crucial for material stability and biological processes.
• Current methods for Aw measurement can be invasive or lack spatial resolution.
• Understanding water's state in hydrated materials is essential for various applications.

Purpose of the Study:

• To develop a noninvasive, in situ method for evaluating water activity (Aw) in hydrated materials.
• To establish a correlation between water's hydrogen-bonding energy and its chemical potential.
• To enable high-spatial-resolution analysis of water states in complex systems.

Main Methods:

• Utilized shortwave infrared (SWIR) spectroscopy to analyze hydrogen-bonding energy of water molecules.
• Developed linear and quadratic models relating hydrogen-bonding energy difference to chemical potential difference.
• Applied the models to sugar solutions, foodstuffs, hydrogels, and electrolyte solutions.

Main Results:

• Established empirical relationships between hydrogen-bonding energy and water activity (Aw).
• Successfully estimated Aw in foodstuffs and hydrogels for Aw > 0.878 (linear) and Aw > 0.675 (quadratic).
• Observed deviations in electrolyte solutions, suggesting additional thermodynamic factors.

Conclusions:

• The SWIR spectroscopy method provides a practical approach for in situ, spatially resolved Aw evaluation.
• This technique is effective for characterizing water states in heterogeneous hydrated materials.
• Further research is needed to account for additional thermodynamic contributions in complex solutions like electrolytes.