Clogging of porous media: from the colloidal particle to the clog – COLLMAT

The structure of the project is structured around the different and consecutive steps of the life of a clog.
First, we will begin with the formation of the clog and then we will focus on the evolution of clog over time under flow.

1-During the first step which corresponds to the nucleation of the clog, we will study the capture conditions of a single particle on the pore surface. We will investigate how these conditions change with different flow velocities, the pore geometry and the chemistry of the suspension. Numerical simulations will be performed in the same time in order to gain a better understanding of the hydrodynamic of the problem.

2-We will then study the formation of aggregates from the pore surface. We will determine the growth conditions (structures and shapes) under strong confinement and under flow

3- In a final step, we will define how the connexion of the aggregates leads to the clogging of the pore.
This first part will allow us to define the general onset conditions of the clog and also the internal structure of concentrated suspension under strong confinement. The results of this first part will help to define the better conditions for the second part.
In this second part, we will study the hydrodynamic resistance and the permeability of the clog as it forms, from thefirst deposited particle to the effective clogging of the pore. In the following, we wiil focus on the evolution its structural properties under flow, once the pore is well formed. We would like to study the coupling between the permeation flow within the clog and its internal structure.

We have shown that there are different pore clogging scenarii in the case of extreme confinement, when the the pore size is a bit bigger than the particle that flows through it (ratio between the pore size to the particle diameter lies between (1.1 and 1.75). We get a phase diagram in which we can clearly distinguish the different zones where the particles are fully transported without being captured when they flow through the pores and those where the pore is clogged. We have also shown that there is a critical rate below which the all the incoming particles are stopped at the entry of the pore and thus clogging it. But above this critical value the particles can invade the pore on it overall length before the pore being clogged. We were able to provide the different behaviors by linking them to the filtration conditions (pore geometry, rate or imposed pressure and ionic strength of the solution). We also link them to the trajectory of the particles we can get from long exposure time fluorescent imaging which give to us acces to the particle dynamics. In this way, we were able to show that the particles already captured at the pore entry enhance the capture of the incoming particles.

In the following year we would like to shed some light on the different mechanisms responsible of the clogging for various pore sizes. We will investigate the overall dynamics of clogging, from the first particles captured by the pore surface to the clog. This project will allow to study the clogging phenomena at the porous media scale.

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I propose to develop the research program described below in the framework of a new research theme that I initiated in March 2010 at the Institut de Physique de Rennes.
Clog formation is a recurrent issue and almost inevitable when a dilute colloidal solution flows through a porous medium. Because of the complexity of the process of clogging, recent studies have focused on clogging at the single pore scale, mainly using microfluidics channels. The reports identify the conditions of adhesion of a single particle to the pore wall. They also indicate that clogging results from a one-by-one deposition of colloids, and the average number of particles that can pass through a pore before it clogs scales with the ratio of pore to particle size. The huge uncertainty on this average number of particles degrades significantly the model’s predictive accuracy. Moreover, we still do not know how the particles accumulate in the pore and eventually clog it. The growth of the aggregate of colloids at the surface of the pore under flow remains unknown.
The general idea of this project is to visualize and understand the different steps of clog formation at the pore and also at the particle level, which is the next essential and necessary step to understand the blockage of real porous media. This experimental project is focused on two main aspects of the clogging:
1-Firstly, our aim is to better understand the overall clogging process. We will start to define the conditions (chemical, hydrodynamic and confinement) for the deposition of the particles on the pore surface. Then we will determine how aggregates start to growth from those monolayers of particles in contact with the walls. We will also study the aggregate stability under flow. Finally, we will study how the growth of several aggregates leads to the complete blockage of the pore.
2- In the second part we would like to first focus on the dynamics at the early stage of clog formation. We will determine both the structure (permeability) of the clog as it forms and the evolution of the corresponding hydrodynamic resistance with the help of a new technique of in silico pressure measurement. We will also study the evolution of the permeability of a clog which is already formed. In these conditions, we will be able to investigate the coupling between the interstitial fluid flow and the motion of the particles within the clog. We want to define how the permeation flow within a dense suspension modifies its structure.