Thèse Mécanique et Relaxation d'Un Assemblage de Colloïdes Sous Forçage Hydrodynamique - Application aux Processus de Filtration H/F - Doctorat.Gouv.Fr

Établissement : Université de Toulouse École doctorale : GEETS - Génie Electrique Electronique,Télécommunications et Santé : du système au nanosystème Laboratoire de recherche : LAAS - Laboratoire d'Analyse et d'Architecture des Systèmes Direction de la thèse : Pierre JOSEPH ORCID 0000000231428996 Début de la thèse : 2027-09-01 Date limite de candidature : 2026-11-23T23:59:59 Comprendre le mécanisme de colmatage d'une membrane de filtration est essentiel pour optimiser son efficacité et prolonger sa durée de vie.

Cette thèse porte sur la stabilité d'un bouchon colloïdal brownien, composé d'une phase réversible (un verre répulsif) et d'une phase irréversible. Les objectifs sont d'obtenir: (i) une cartographie des régimes de stabilité et des taux d'irréversibilité des bouchons colloïdaux Browniens dans une puce microfluidique; (ii) une caractérisation de la dynamique de relaxation après l'arrêt de l'écoulement; et (iii) les propriétés (poro)mécaniques d'un bouchon colloïdal. L'ensemble des résultats expérimentaux servira de base à une modélisation visant à interpréter et prédire le comportement d'un bouchon colloïdal formé sous écoulement. Understanding how a filtration membrane becomes clogged is crucial for improving its efficiency and lifetime. Over the past twenty years, the use of microfluidics to investigate the fundamental mechanisms of clogging at the particle/pore scale has led to significant advances concerning particle capture on the walls of porous media, as well as the kinetics and dynamics of clogging. However, no study has focused on the stability of a clog made of colloids, let alone in the presence of Brownian motion.
Our recent work on the microstructure of a clog has revealed its heterogeneity, with the observation of clogs exhibiting a phase with an amorphous structure near the pore and another, crystalline, farther from the pore. Preliminary observations have shown that when the flow is stopped, part of the clog re-suspends. The clog is thus composed of a reversible phase (a repulsive glass) and an irreversible one. This observation raises fundamental questions: which parameters determine the irreversibility rate of the clog, and thus its stability but also its resistance to cleaning? What differences arise between a clog formed under constant flow rate and one formed under constant pressure? The irreversibility appears to involve a competition between the flow and the repulsive interactions between particles, which must be demonstrated experimentally. Furthermore, what is the relaxation dynamics of the clog when the stabilizing flow disappears? What is the influence of Brownian motion?
In addition, we already observed that the clog deforms under variable forcing. What are the elastic properties of such a clog? Can they be changed dynamically by changing the salt concentration? How does confinement affect these properties? Are irreversibility and elastic properties related, and how? These questions relate to recent developments in soft matter and poromechanics research. The previous questions structure the objectives of this PhD: to obtain (i) a mapping of the stability regimes and irreversibility rates of clogs of Brownian colloids in a microfluidic chip, (ii) a characterization of the relaxation dynamics after flow stoppage, and (iii) the (poro)mechanical properties of a colloidal clog.
The global scientific objective is to gain understanding in irreversibility, relaxation dynamics and mechanical properties of clogs, following an approach involving well-controlled configurations thanks to microfluidics and modelling. The proposed approach relies on well-established design and experimental tools. The PhD candidate will first design a new microfluidic chip geometry adapted to this study, and will then fabricate chips in an elastomer (PDMS). The PhD student will conduct experimental campaigns to investigate the unclogging of Brownian colloid clogs in these chips, with data acquisition combining fluorescence and confocal microscopy. Then, a second generation of chips will be designed and exploited, based on the results obtained with the first ones. In addition, the PhD candidate will process and analyze the acquired data using existing Python and/or Matlab routines. Finally, the PhD student will actively participate to modelling the system and compare to the experimental results.

Les candidats doivent posséder une formation universitaire en physique/physico-chimie, en mécanique des fluides/hydrodynamique ou en génie chimique. Une expérience ou un intérêt marqué pour la microfluidique expérimentale, notamment la conception et la fabrication de puces, serait un atout. La maîtrise de la microscopie à fluorescence et/ou confocale, ainsi que du traitement et de l'analyse des données à l'aide de Python et/ou Matlab, est un avantage. Un intérêt pour la modélisation et la comparaison des résultats analytiques et des simulations avec les résultats expérimentaux (dans le domaine de la matière molle et de la poromécanique) sera apprécié.

Application link: https://edd-projets.utoulouse.fr/

• Python
• Analyse de données
• Mécanique des fluides
• MATLAB