Particle Deposition in Drying Porous Media

Abstract

The drying of porous media is a ubiquitous phenomenon in soils and building materials. The fluid often contains suspended particles. Particle deposition may modify significantly the final material, as it could be pollutants or clogging the pores, decreasing the porosity, such as in salt, in which particles and drying kinetics are coupled. Here, we used SEM and X-ray microtomography to investigate the dried porous media initially saturated by nanoparticle suspensions. As the suspensions were dried, nanoparticles formed a solid deposit, which added to the initial solid matrix and decreased the porosity. We demonstrate that since the drying occurred through the top surface, the deposit is not uniform as a function of depth. Indeed, the particles were advected by the liquid flow toward the evaporative surface; the deposit was significant over a depth that depended on the initial volume fraction, but the pore size was affected over a very narrow length. These findings were interpreted in the frame of a physical model. This study may help to design better porous media and take into account particle influence in drying processes.

Understanding the drying mechanism of straw substrate culture block: Physicochemical properties, pore structure, and drying optimization

“…We used the “plot profile” tool in the “analyze” option to generate a line plot of the distance versus the grayscale value, which was used to represent the grayscale change in the rectangular box—the grayscale changes in the range through which the box is selected. The magnitude of the grayscale change per unit distance indicates pore size, and the continuity of the magnitude of the grayscale change indicates the pore coverage pattern [ 33 ]。…”

Visualization of the Sol–Gel Transition in Porous Networks Using Fluorescent Viscosity-Sensitive Probes

“…In general, investigating the kinetics of such phenomena in porous materials is quite complex, as it requires the combination of different advanced imaging techniques, such as nuclear magnetic resonance (NMR) to visualize the saturation profiles of the liquid and X-ray microtomography to visualize microscale changes in the porous matrix such as salt precipitation or colloidal deposits. In this way, previous investigations of drying of colloidal suspensions and ionic solutions in stones have revealed accumulation of particles , or salts at the evaporative surface of the porous media, not unlike the famous “coffee stain effect” for evaporating drops . However, the dynamics of gelation in confinement is still poorly understood as multiple physical phenomena will occur during liquid flow and phase change, including a viscosity increase and mass transport due to evaporation of the solvent.…”

“…Similar results were reported for particle deposition in porous media. 6,7 In porous media, the velocity of liquid flows by capillarity at the surface v cap can be approximated by Darcy's d exceeds v cap , the velocity at which the liquid reaches the evaporation surface. From that point onward, the solution continues to evaporate inside the porous media, and the vapor diffuses over an increasing length scale.…”

“…Chemical reactions during the sol−gel transition of methyltriethoxysilane; (2) dynamic light scattering measurements during the sol−gel transition of MTEOS; (3) fluorescence properties of 4-DASPI inside MTEOS solution; (4) sol−gel transition of MTEOS droplets using time-resolved fluorescence microscopy;(5) evolution of the surface tension and contact on glass capillary wall of MTEOS during the sol−gel transition; (6) more measurements about the skin formation in round capillaries;(7) protocol to manufacture 2D model porous media (PDF)…”

“…Similar results were reported for particle deposition in porous media. 6 , 7 In porous media, the velocity of liquid flows by capillarity at the surface v cap can be approximated by Darcy’s law where μ is the viscosity of the liquid, k the permeability of the network, and the capillary pressures in the pores network, function of the contact angle, and surface tension of the solution. We show in the SI that both the variation of the contact angle and the surface tension of the solution are insignificant compared to the increase in viscosity.…”