Orateurs invités

   L. Bocquet       L. Brochard     C. De Tomas       J. Druhan         R. Helmig       S. Lorthois

          Lydéric Bocquet

Lydéric Bocquet is a CNRS researcher and attached Professor at Ecole Normale Supérieure (Paris) working at the Laboratoire de Physique de l’Ecole normale suprieure LPENS. He is a member of the French Academy of Sciences.

His research is at the interface between condensed matter, fluid dynamics, and nano-science. With his research team they combine experiments, theory, and molecular simulations to explore the mechanisms of the dynamics of fluid interfaces from the macroscopic down to molecular level. His team developed unique experiments to study fluid transport using nanofluidics.

His fundamental research has led to the creation of four start-ups, including Sweetch Energy in the field of osmotic energy and Hummink in the field of additive manufacturing on a nanometric scale.

          Laurent Brochard

Laurent Brochard is a researcher at Navier lab (ENPC, Univ. Gustave Eiffel, CNRS) since 2012, and professor at École nationale des ponts et chaussées (ENPC) since 2023. He received his Ph.D. from Université Paris-Est in 2011. He is also engineer from École Polytechnique (France) and from École nationale des ponts et chaussées (France).

 His research focuses on multi-scale approaches for the study of the physics and mechanics of materials with emphasis on phenomena that have their origin at the molecular scale: adsorption and poromechanics, fracture mechanics and failure initiation, thermo-mechanical couplings, and confined phase transition. Targeted applications are mostly in geomechanics (CO2 sequestration, nuclear waste and energy storage, earth and bio-sourced construction, cementitious materials, and fault stability).

Abstract:

Poromechanics of microporous media

Microporous media, with pores less than 2 nm large, are known to exhibit complex poromechanical behaviors because the fluid in such small pores is adsorbed and is no more bulk. Well known examples are the deformations of clay or wood induced by humidity. Much progress has been made in the recent years to understand and model the poromechanics under adsorption, and, in this presentation, I will focus more specifically on the contribution of molecular simulation. As a first approach to the problem, we will see how molecular fluctuations observed at very small scale fully characterize the poromechanics, irrespective of the nanostructure of the material. In the particular case of well-defined pore shapes (e.g., slit pores), one can define the concept of porosity, which makes it possible to develop a second approach of poromechanics, more detailed, where one distinguishes the behavior of the fluid from that of the solid. In both cases, molecular simulation is essential to capture the poromechanical effect of the fluid, at a scale hardly accessible to experiments. As illustrations, we consider the case of amorphous cellulose for the first approach and of swelling clay for the second approach. 
Fluctuations of physical quantities are ubiquitous in molecular simulations at the atomic scale because of the thermal agitation. It is well known that the magnitude of the fluctuations of thermodynamic state parameters are related to the second order derivatives of the thermodynamic potential minimum at equilibrium (e.g., compressibility, thermal expansion, and heat capacity for a fluid). While fluctuation formulas are well established for simple systems (e.g., pure fluids), in the field of porous media only the isosteric heat of adsorption is commonly estimated from fluctuations, and the formula considered assumes a rigid solid. Here, we revisit the Biot-Coussy theory of thermo-poro-elasticity in a framework adapted to derive fluctuation formulas. All the thermo-poro-mechanical moduli can then be characterized by fluctuations of quantities readily accessible during a molecular simulation, i.e., with no additional computational cost and with no need to define the concepts of porosity or specific surface (ambiguous at the molecular scale). These fluctuation formulas are valid even when the fluid is adsorbed and induces unusual couplings. It is therefore possible to use the formulas to fully characterize the mechanical and thermal effects of adsorption, and conversely to characterize the adsorption response to stress and temperature. The application of these fluctuation formulas is illustrated in the case of amorphous cellulose submitted to moisture, which exhibits many unusual couplings beyond swelling (negative drained thermal expansion, very high drained heat capacity, negative Biot modulus…). 
In some microporous media, such as layered clay minerals, one can define the concept of porosity and therefore distinguish between the solid and fluid phases. Doing so, it is then possible to characterize the property of the adsorbed fluid and of the solid skeleton separately. Considering the case of water confined in sodium montmorillonite, one finds that the thermo-mechanical properties are significantly affected by adsorption. Even more confusing, one finds that the Gibbs-Duhem equation no more applies, which means that the behavior of the adsorbed fluid is described by a total of 6 moduli instead of 3 for a bulk fluid. This conceptual change calls for an entirely new formulation of poromechanics. We propose such a formulation of non-linear thermo-poro-mechanics and apply it to explain two thermo-mechanical anomalies of clays: 1- the excessive thermal pressurization of interstitial water during undrained heating, and 2- the very large drained thermal expansion of over-consolidated clays. The fine analysis of these tests is quite instructive regarding the underlying physics. For instance, the excess thermal pressurization of water during undrained heating is not because bound water has a larger thermal expansion than free water (it is smaller actually), but because there is a net transfer from the bound water to the free water.

          Carla De Tomas

Carla de Tomas is a Senior Lecturer in Net Zero in the Department of Physics and a member of the Net Zero Centre, King's College London. She holds a PhD in Physics from the Autonomous University of Barcelona and has built a multidisciplinary research career at the intersection of materials science, energy storage, and computational modelling. Her research interests focus on disordered carbon materials due to their sustainability and tunability to target a wide variety of technological applications, in particular ion batteries, gas storage and air and water purification. Her computational group is dedicated to working closely with experimentalists, using high-throughput atomistic simulations and machine-learning-based tools to guide the rational design of active materials for target applications. Prior to joining King's, she held positions in Imperial College London (Marie Skłodowska-Curie Fellow), the University of Tokyo (JSPS Postdoctoral Fellow) and Curtin University (Research Associate). In addition, she has industrial expertise from her role as Senior Computational Materials Scientist at Happy Electron Ltd., a London-based battery start-up. She currently serves as an Editorial Associate for Carbon, the leading journal in carbon science, and is a member of the British and the Australian Carbon Societies.

          Jennifer L. Druhan

Jennifer L. Druhan is Associate Professor at the University of Illinois Urbana-Champaign since 2015 in the Department of Earth Science & Environmental Change. Since 2019 she is also Professeure Associée at Institut de Physique du Globe de Paris.

Her research interests center around the ability to identify the underlying processes contributing to chemical variability during reactive transport through porous media using measurements and modeling of associated stable isotope fractionations. Her recent work has involved integrating stable isotope systems in numerical models of reactive flow and transport to unravel the internal watershed structure and function and emerging stream concentration-discharge relationships

abstract:

A reactive transport framework for addition of exogenous solids to eroding porous media

Soils emerge as a balance between the pace of bedrock uplift and erosion, the velocity of meteoric fluid infiltration and drainage, and the rate of chemical weathering reactions. Together, these timescales combine to set the thickness, chemical composition and utility of soils as a foundation for ecosystems and agriculture. Reactive transport models (RTMs) for pedogenesis generally utilize a reference frame in which bedrock supplied from below is converted into erosion of soils at the land surface. However, a variety of pathways lead to differential movement of solid phases in otherwise uplifting porous media. For example, vegetation pushes root structures downward into actively developing soils, exogenous dust inputs infiltrate soil profiles despite erosion and recent carbon sequestration strategies propose to amend agricultural soils with highly weatherable minerals to promote conversion of CO₂ to carbonate alkalinity. These conditions call for the necessity of RTMs capable of treating the differential movement of solids within porous media. Here we modify the open source CrunchTope RTM software to quantitatively interpret the impacts of dust deposition and solubilization in stream water chemistry, regolith weathering rates, and ecosystem nutrient availability. We describe two simulations: (1) a generic model demonstrating a simplified system in which bedrock uplift and soil erosion occur in tandem with solid phase dust deposition at the land surface; (2) a case study based on a small (0.54 km²) upland Mediterranean watershed located on Mont Lozère in the National Park of Les Cévennes, France.

         Prof. Rainer Helmig

Prof. Rainer Helmig is the head of the Institute for Modelling Hydraulic and Environmental Systems, Department of Hydromechanics and Modelling of Hydrosystems at the University of Stuttgart, Germany. He is the Kimberly-Clark Distinguished Lecturer 2025 of the International Society for Porous Media.

Rainer Helmig is widely recognized as a pioneer and visionary in developing numerical modelling concepts in the fields of groundwater hydrology, subsurface energy storage, and coupled processes at the interface between porous media and free-flow compartments. 
Over the course of his illustrious career, Rainer Helmig has consistently produced groundbreaking research that has pushed the boundaries of knowledge in the field of porous-media research. His work has been instrumental in solving real-world problems, his methodologies have been adopted widely and have had a transformative impact on the field. Beyond his research contributions, Rainer Helmig has been a dedicated mentor and educator, nurturing the talents of emerging scientists and engineers in the field.

abstract:

From the brain to water uptake of roots to fuel cells:  - porous media are "almost" everywhere –

Porous media are almost everywhere. The understanding of flow, transport and deformation processes in porous media is important for the optimization of fuel cells, energy storage, the prediction of landslides due to heavy rainfall or the spread of tumors in human tissue. 
In this lecture, we will give a first a brief overview of the importance of porous media; using selected examples, we will cover the range from environmental to technical and relevant bio-issues.
In the second part, we would like to present selected modelling approaches and analyses using two concrete application examples:
•    Firstly, for the release multiple sclerosis, we can use knowledge about prose media to help make better predictions. What happens in the porous medium "brain" when the blood-brain barrier no longer functions properly? How can research in the field of porous media positively influence the treatment of multiple sclerosis?
•    On the other hand, I would like to discuss with you whether we can improve water management in fuel cells as a drive technology with our knowledge of porous media. What role does the understanding of porous media play in the context of alternative forms of mobility such as fuel cells? Are our "classical models" for water transportation helpful?
This is where simulations help, because they make the invisible processes in the brain and in the fuel cell visible (I hope).

         Sylvie Lorthois

Sylvie Lorthois is a CNRS Research Director in the Porous and Biological Media group of the Fluid Mechanics Institute of Toulouse. After an engineering degree and a master's degree in fluid mechanics obtained at Sup'aéro, Toulouse, in 1995, she diversified her training in 1996 with a master's degree in vascular biology from the Medical School of Paris Sud University. Her PhD, defended in 1999 at the National Polytechnic Institute of Toulouse, focused on occlusive pathologies of the cerebral macro-circulation. She joined the CNRS in 2001 after a post-doctoral stay at the University of California at Berkeley, where she learned about the fundamental principles of Magnetic Resonance Imaging.

She is now interested in all aspects of brain microcirculation (morphogenesis and architecture, blood flow and transport, regulation and application to functional brain imaging, interaction with cerebro-spinal/interstitial fluid flow, involvement in brain pathologies, ...), which she approaches mainly from a theoretical and numerical modeling perspective. For that purpose, she collaborates on a regular basis with biologists, physiologists and clinicians. In parallel, she also works on the physics of red blood cell flow in networks, which she approaches mainly based on microfluidic

abstract: 

Modeling blood flow and mass transfers within the brain to highlight the vascular component of Alzheimer’s Disease

Because the brain lacks any substantial energy reserves, the cerebral microvascular system is essential to a large variety of physiological processes in the brain, such as blood delivery and local blood flow regulation as a function of neuronal activity. It provides a unique window to observe the functioning brain using hemodynamically-based functional imaging techniques. It also plays a major role in disease (stroke, neurodegenerative diseases, …). However, the functional consequences of vascular damage (including acute occlusions or long-term remodeling in ageing or disease) are poorly understood.

In this context, modeling approaches are increasingly important, and can be inspired by those developed for the study of multiphase or reactive flows in porous media, subsequently enriched to take into account the specific architecture of the microvascular network. This enables to obtain the corresponding scaling-laws for blood flow and mass transport. I will discuss how these scaling-laws are mostly driven by the topology of the microvascular network and highlight how they help understand the vascular component of Alzheimer’s Disease.