Characterizing Hygroscopic Materials via Droplet Evaporation

Area of Science:

• Materials Science
• Physical Chemistry
• Chemical Engineering

Background:

• Hygroscopic materials are crucial desiccants in various industries, including food, packaging, and gas storage.
• Existing methods for quantifying hygroscopicity, such as tandem differential mobility analyzers and gravimetric vapor sorption analyzers, are complex and costly.
• A simpler, more accessible method is needed to characterize material hygroscopicity.

Purpose of the Study:

• To develop a straightforward technique for measuring the hygroscopicity of bulk materials.
• To establish a new, simple metric for material hygroscopicity that is easy to interpret and apply.

Main Methods:

• Developed a method involving suspending a bulk material above a deposited droplet.
• Measured the droplet's evaporation rate under controlled temperature conditions (dew point).
• Applied Fick's law to calculate the effective water vapor concentration and derived a dimensionless hygroscopic index.

Main Results:

• Demonstrated that droplet evaporation rate directly correlates with diffusive transport into the hygroscopic material.
• Successfully extracted effective water vapor concentration and calculated a hygroscopic index (0 to 1).
• The hygroscopic index is equivalent to 1 - water activity (a_w).

Conclusions:

• The proposed method offers a simple and effective way to characterize material hygroscopicity.
• The derived hygroscopic index provides a valuable metric for material assessment, correlating with water activity.
• This technique has broad applicability for evaluating desiccants in diverse industrial applications.