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Journal ArticleDOI

Microstructure of the near-wall layer of filtration-induced colloidal assembly.

04 Nov 2020-Soft Matter (The Royal Society of Chemistry)-Vol. 16, Iss: 42, pp 9726-9737
TL;DR: An experimental study of filtration of a colloidal suspension using microfluidic devices involving colloid-colloid repulsive interactions and fluid velocity, which shows some heterogeneity in the near-wall layer microstructure.
Abstract: This paper describes an experimental study of filtration of a colloidal suspension using microfluidic devices. A suspension of micrometer-scale colloids flows through parallel slit-shaped pores at fixed pressure drop. Clogs and cakes are systematically observed at pore entrance, for variable applied pressure drop and ionic strength. Based on image analysis of the layer of colloids close to the device wall, global and local studies are performed to analyse in detail the near-wall layer microstructure. Whereas global porosity of this layer does not seem to be affected by ionic strength and applied pressure drop, a local study shows some heterogeneity: clogs are more porous at the vicinity of the pore than far away. An analysis of medium-range order using radial distribution function shows a slightly more organized state at high ionic strength. This is confirmed by a local analysis using two-dimension continuous wavelet decomposition: the typical size of crystals of colloids is larger for low ionic strength, and it increases with distance from the pores. We bring these results together in a phase diagram involving colloid–colloid repulsive interactions and fluid velocity.

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This is an author’s version published in: https://oatao.univ-toulouse.fr/2 74 62
To cite this version:
Mokrane, Mohand Larbi and Desclaux, Térence and Moris, Jeffrey F. and Joseph,
Pierre and Liot, Olivier
Microstructure of the near-wall layer of filtration-induced
colloidal assembly. (2020) Soft Matter, 16 (42). 9726-9737. ISSN 1744-683X .
Official URL:
https://doi.org/10.1039/D0SM01143F
Open Archive Toulouse Archive Ouverte





Citations
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Journal ArticleDOI
TL;DR: In this article, the authors explore fouling through microfluidic systems, assessing the fundamental interactions involved and how micro-fluidics enables the comprehension of the mechanisms characterizing the process.
Abstract: The almost ubiquitous, though undesired, deposition and accumulation of suspended/dissolved matter on solid surfaces, known as fouling, represents a crucial issue strongly affecting the efficiency and sustainability of micro-scale reactors. Fouling becomes even more detrimental for all the applications that require the use of membrane separation units. As a matter of fact, membrane technology is a key route towards process intensification, having the potential to replace conventional separation procedures, with significant energy savings and reduced environmental impact, in a broad range of applications, from water purification to food and pharmaceutical industries. Despite all the research efforts so far, fouling still represents an unsolved problem. The complex interplay of physical and chemical mechanisms governing its evolution is indeed yet to be fully unraveled and the role played by foulants' properties or operating conditions is an area of active research where microfluidics can play a fundamental role. The aim of this review is to explore fouling through microfluidic systems, assessing the fundamental interactions involved and how microfluidics enables the comprehension of the mechanisms characterizing the process. The main mathematical models describing the fouling stages will also be reviewed and their limitations discussed. Finally, the principal dynamic investigation techniques in which microfluidics represents a key tool will be discussed, analyzing their employment to study fouling.

8 citations

Journal ArticleDOI
TL;DR: In this article , the formation of a stable arch of particles at a constriction that hinders the transport of particles downstream of the clog was studied. But the authors focused on the role of the volume fraction of the suspension on the clogging dynamics.
Abstract: Clogging can occur whenever a suspension of particles flows through a confined system. The formation of clogs is often correlated to a reduction in the cross-section of the channel. In this study, we consider the clogging by bridging, i.e., through the formation of a stable arch of particles at a constriction that hinders the transport of particles downstream of the clog. To characterize the role of the volume fraction of the suspension on the clogging dynamics, we study the flow of particulate suspensions through 3D-printed millifluidic devices. We systematically characterize the bridging of non-Brownian particles in a quasi-bidimensional system in which we directly visualize and track the particles as they flow and form arches at a constriction. We report the conditions for clogging by bridging when varying the constriction width to particle diameter ratio for different concentrations of the particles in suspension. We then discuss our results using a stochastic model to rationalize the influence of solid fraction on the probability of clogging. Understanding the mechanisms and conditions of clog formation is an important step for optimizing engineering design and developing more reliable dispensing systems.

6 citations

Journal ArticleDOI
TL;DR: In this article, the influence of the porous membrane morphology on crystal formation and compaction behavior of soft filter cakes under dead-end filtration conditions was analyzed by optical visualization and pressure data.
Abstract: Filter cake formation is the predominant phenomenon limiting the filtration performance of membrane separation processes. However, the filter cake’s behavior at the particle scale, which determines its overall cake behavior, has only recently come into the focus of scientists, leaving open questions about its formation and filtration behavior. The present study contributes to the fundamental understanding of soft filter cakes by analyzing the influence of the porous membrane’s morphology on crystal formation and the compaction behavior of soft filter cakes under filtration conditions. Microfluidic chips with nanolithographic imprinted filter templates were used to trigger the formation of crystalline colloidal filter cakes formed by soft microgels. The soft filter cakes were observed via confocal laser scanning microscopy (CLSM) under dead-end filtration conditions. Colloidal crystal formation in the cake, as well as their compaction behavior, were analyzed by optical visualization and pressure data. For the first time, we show that exposing the soft cake to a crystalline filter template promotes the formation of colloidal crystallites and that soft cakes experience gradient compression during filtration.

5 citations

Journal ArticleDOI
TL;DR: In this paper , the relative contribution of the confinement dimensions, the ionic strength and the flow conditions on the particle volume fraction of the resultant accumulation is determined, and it is shown that in high confinement the irreversible deposition of particles on the channel surfaces controls the structure of the accumulation, and thus the flow through it, irrespective of the other conditions, leading to a Darcy flow.
Abstract: When a colloidal suspension flows in a constriction, particles deposit and are able to clog it entirely, this fouling process being followed by the accumulation of particles. The knowledge of the dynamics of formation of such a dense particle assembly behind the clog head and its structural features is of primary importance in many industrial and environmental processes and especially during filtration. While most studies concentrate on the conditions under which pore clogging occurs, i.e., the pore narrowing up to its complete obstruction, this paper focuses on the accumulation of particles that follows pore obstruction. We determine the relative contribution of the confinement dimensions, the ionic strength and the flow conditions on the permeability and particle volume fraction of the resultant accumulation. In high confinement the irreversible deposition of particles on the channel surfaces controls the structure of the accumulation and the flow through it, irrespective of the other conditions, leading to a Darcy flow. Finally, we show that contrarily to the clog head, in which there is cohesion between particles, those in the subsequent accumulation are held together by the fluid and form a dense suspension of repulsive hard spheres.
References
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Journal ArticleDOI
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Journal ArticleDOI
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TL;DR: In this article, the authors investigated the aggregation of three chemically different colloidal systems under both diffusion-limited and reaction-limited aggregation conditions and provided convincing experimental evidence that the two regimes of aggregation are indeed universal.
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880 citations

Journal ArticleDOI
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845 citations