The Effect of Air and Water Phase Configuration on Colloid Retention in Partially Saturated Porous Media.

In a partially saturated system the accumulation of colloid at interfaces such as air-water (AW), solid-water (SW) and air-water-solid (AWS) interfaces depend on the area of those interfaces and its accessibility to the water phase. Accumulations of colloids near the three-phase contact line (AWS) depend on the water volume associated with that line. The area of interfaces and contact line can be varied independently by adjusting the capillary pressure (or moisture content) and/or contact angle. In the present study, we keep the contact angle constant and vary only moisture content  to vary interface configurations and areas of AW and AWS interfaces. Experiments are being conducted using 3D pore-scale micromodels, made from rectangular m-slide (Ibidi) with inner dimension of 400 μm by 3800 μm, packed with glass beads which have average diameter of 180 μm, and with fluorescent latex microspheres with diameter of 1 μm. Both capillary tube and glass beads were treated to achieve uniform hydrophilic surface. Using a fast laser scanning microscope, volumetric (3D) images are collected in near real time during dynamic flow conditions as well as static conditions. The images will allow for investigation of the air and water phase configurations and its effect on colloid retention at the interfaces. An advanced confocal software Volocity is used for particle tracking and image analysis to quantify the number of particles retained for specified areas.