(95b) Advancing and Receding Contact Angles of Powders Measured in a Closed Column

Wettability of powders by liquids is important for many industrial manufacturing processes including granulation, dissolution and filtration and is usually characterized in terms of the solid-liquid contact angle. The usual way to measure contact angle between liquids and powders is the Washburn capillary rise method using an open column that is filled with the powder of interest. In this work, we discuss the advantages of using a closed column instead, to study both the advancing and receding contact angles. Using a closed column also enables us to investigate the dynamics during imbibition. We shall also discuss the advantages of monitoring the pressure increase compared to the measuring the amount of liquid uptake or the front position by optical means. We shall also present analytical solutions in terms of pressure, liquid uptake and liquid front as a function of time including gravity effects. To validate the results we performed experiments using glass beads to create an unconsolidated porous media representing a powder bed inside a closed column. By fitting these solutions to experiments, we are able to determine both the permeability and contact angles of the porous media. Finally, we shall discuss the possibility of performing fast characterization experiments using short columns.