borosilicate beads (negatively charged, 63 μm average 66 diameter) randomly packed (porosity ϕ 0 ¼ 0.38) in a 67 square glass capillary (width w ¼ 1.0 mm), and we invade 68 this medium with positively charged, fluorescent, mono-69 disperse (diameter d p ¼ 1.0 μm) latex colloids. The 70 suspensions are made at constant dilute concentration C 0 ¼ 71 20 mg mL −1 in a mix of deionized water and DMSO to 72 match the refractive index of the beads [28]. This allows us 73 to visualize the particles inside the porous medium by 74 confocal microscopy. The opposite charges of the beads 75 and the particles fosters particle adsorption at the surface of 76 the beads. Particle-particle bonding may be promoted by 77 screening the interparticle repulsion (i.e., decreasing the 78 Debye length) through an increase of the ionic strength I by 79 addition of salt (sodium iodide) [29]. 80 A test consists of continuously injecting a suspension in 81 the porous medium (initially saturated with liquid) 82 and tracking the particle deposition inside the medium. 83 Except when mentioned, we impose a constant flow rate
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