78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

P008: Seeing the Unseen: Visualizing Particle Movement in Hydrogel Beds

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The size and density of a smaller rigid sphere affect its movement when released from rest into a static bed of larger soft hydrogel particles immersed in an index-matched mixture of water and PEG. Compressing the bed with an overburden pressure of six layers of hydrogel particles located above the air-water interface reduces the average pore throat diameter via bed particle compression. Smaller, denser rigid spheres come to rest deeper in the bed than larger, less-dense spheres because the former are not trapped by size and can squeeze through more pores that would otherwise block their passage in the absence of bed particle deformation due to their higher density.