Wettability of hydrophobic silica aerogel granules and powders

The state of the art for characterizing the wettability of silica aerogel granules and powders heavily relies on the use of static contact angle measurements obtained through goniometer experiments. However, measuring contact angles of (super)hydrophobic silica aerogel granules and powders might give inaccurate results and are prone to user errors due to the high contact angles coupled with the rough and irregular nature of the powder beds. In this study, goniometry of three different types of silica aerogel granules are studied as a reference and critically assessed. Here, it is shown that the aerogels have similar apparent static contact angles and significant differences might occur from experimental parameters or user error. Afterwards, a Wilhelmy plate-based approach is implemented increasing the accuracy and precision of the wetting measurements compared to goniometry by measuring the receding contact angle. Additionally, a series of other characterization tools, including X-ray computed tomography and radiography, dynamic vapor sorption and inverse gas chromatography, are utilized to support conclusions drawn from the tensiometer experiments. These surface characterization tools confirm the same trend in hydrophobicity of the different types of silica aerogel granules.