Stephane Rodts

Gustave Eiffel University · Laboratoire NAVIER

This study concerns the spatial evolution of the internal components of a macroscopic sample of cellulose slurry during its convective drying. In a first stage, some water is extracted which induces a shrinkage of the structure, the sample remaining saturated, i.e. the solid porous structure made of fibers in contact remains filled with water. In a...

From Magnetic Resonance Imaging (MRI) measurements allowing to distinguish separately the density distribution of the two phases of the system, we show that bitumen emulsions essentially dry homogeneously, with nevertheless a slight concentration gradient increasing towards the sample free surface exposed to air. Remarkably, despite the resulting l...

Water inside hygroscopic porous media such as plantlike systems can be found either freely penetrating in capillaries or absorbed into the solid phase (bound water). Here we demonstrate that the wetting properties (contact angle) of liquid along cell walls significantly depend on the amount of bound water absorbed: a change from poor to good wettin...

Two-dimensional proton nuclear magnetic resonance (2D ¹ H NMR) relaxometry is increasingly used in the field of wood sciences due to its great potential in detecting and quantifying water states at the level of wood constituents. More precisely, in this study, this technique is used to investigate the changes induced by “natural” and “artificial” a...

2D Magnetic Resonance images showing water imbibition from a shrinking paste to a (larger pores) bead packing at different times.

The convective drying of a composite system made of a porous medium covered with a paste is a situation often encountered with soils, roads, building and cultural heritage materials. Here we discuss the basic mechanisms at work during the drying of a model composite system made of a homogeneous paste covering a simple granular packing. We start by...

In this study, methane hydrate-bearing sand (MHBS) was created in the laboratory following two methods in order to obtain two types of gas hydrate morphology in sandy sediment. The hydrate morphology in the sediment was assessed by measuring the compressional wave velocity combined with models to predict the wave velocities of the sediment containi...

Methane hydrates, being solid ice-like compounds of methane and water, form naturally at high pressures and low temperature. They are considered as a potential future energy resource but also as a considerable geo-hazard. Methane hydrate dissociation during borehole drilling and production process (by heat or depressurization methods) may reduce th...

From direct observations and MRI measurements we demonstrate that during the drying of a direct (oil in water) emulsion the whole system essentially concentrates homogeneously, which leads to shrinkage, without air penetration. The structure and mechanical strength (i.e. the elastic modulus) of this concentrated bulk are not significantly different...

Methane hydrate is being considered as a potential future energy source but may at the same time constitute a considerable geo-hazard. In the present study, methane hydrate bearing sand sediment was created by pressurizing methane gas into previously moistened, then chilled, packed sand specimen (excess gas method). The excess gas was then replaced...

From observations of the progressive deposition of noncolloidal particles by geometrical exclusion effects inside a 3D model porous medium, we get a complete dynamic view of particle deposits over a full range of regimes from transport over a long distance to clogging and caking. We show that clogging essentially occurs in the form of an accumulati...

When dealing with unsaturated wet granular materials, a fundamental question is: what is the effect of capillary cohesion on the bulk flow and yield behavior? We investigate the dense-flow rheology of unsaturated granular materials through experiments and discrete element simulations of homogeneous, simple annular shear flows of frictional, cohesiv...

When dealing with unsaturated wet granular materials, a fundamental question is: what is the effect of capillary cohesion on the bulk flow and yield behavior? We inwestigate the dense flow rheology of unsaturated granular materials through experiments and discrete element simulations of homogeneous, simple annular shear flows of frictional, cohesiv...

When dealing with unsaturated wet granular materials, a fundamental question is: what is the effect of capillary cohesion on the bulk flow and yield behavior? We inwestigate the dense flow rheology of unsaturated granular materials through experiments and discrete element simulations of homogeneous, simple annular shear flows of frictional, cohesiv...

We use magnetic resonance imaging to follow the adsorption of colloids during their transport through a porous medium (grain packing). We injected successive pulses of a suspension of nanoparticles able to adsorb onto the grains. To get quantitative information we carry out 2D imaging and 1D measurements of the evolution in time of the distribution...

Magnetic resonance imaging visualization down to nanometric liquid films in model porous media with pore sizes from micro- to nanometers enables one to fully characterize the physical mechanisms of drying. For pore size larger than a few tens of nanometers, we identify an initial constant drying rate period, probing homogeneous desaturation, follow...

----> Click on https://authors.elsevier.com/a/1VFAw9pi-ESWM to download a free copy of the paper until August 9 2017.<---- Colloidal particles can act as vectors of adsorbed pollutants in the subsurface, or be themselves pollutants. They can reach the aquifer and impair groundwater quality. The mechanisms of colloid transport and deposition are oft...

We show that it is possible to follow the liquid transfer between a cement paste and a porous medium in contact with it, by analysing the evolution of the distribution of ¹H NMR relaxation times. This in particular makes it possible to see that whatever the initial water fraction in the paste, a porous medium with sufficiently small pores can rapid...

Earlywood (EW) and latewood (LW) have different hygromechanical behaviors, if subjected to relative humidity (RH) variations. To understand this effect better, the adsorption mechanisms of EW and LW of Douglas fir were studied by 2D ¹H NMR relaxometry under conditions of equilibrium moisture content (EMC) at 20°C. Two bound water components were de...

Soil contamination is still poorly understood and modeled in part due to the difficulties of looking inside the “black box” constituted by soils. Here, we investigated the application of a recently developed 1H NMR technique to 19F NMR relaxometry experiments and utilized the results as inputs for an existing model. This novel approach yields 19F T...

The desiccation of porous materials encompasses a wide range of technological and industrial processes and is acutely sensitive to the hierarchical structure of the porous materials resulting in complex dynamics which are challenging to unravel. Macroscopic observations of the surface and geometry of model colloidal gels during desiccation under co...

We measure the dispersion coefficient through homogeneous bead or sand packings at different flow rates from direct magnetic resonance imaging (MRI) visualizations of the transport characteristics of a pulse of paramagnetic nanoparticles. Through two-dimensional imaging we observe homogeneous dispersion inside the sample, but we show that entrance...

We measure the dispersion coefficient through homogeneous bead or sand packings at different flow rates from direct MRI visualizations of the transport characteristics of a pulse of paramagnetic nanoparticles. Through 2D imaging we observe homogeneous dispersion inside the sample, but we show that entrance effects may induce significant radial hete...

Polymers suspended in granular packings have a significant impact on water retention, which is important for soil irrigation and the curing of building materials. Whereas the drying rate remains constant during a long period for pure water due to capillary flow providing liquid water to the evaporating surface, we show that it is not the case for a...

Two NMR data acquisition protocols together with corresponding data processing algorithms for locating macroscopic objects, measuring distances between them or monitoring their displacements or deformations with microscopic precision are presented and discussed. The performance of the methods is demonstrated by applying them to the measurement of d...

Direct observations of the surface and shape of model nano-colloidal gels associated with measurements of the spatial distribution of water content during drying show that air starts to significantly penetrate the sample when the material stops shrinking. We show that whether the material fractures or not during desiccation, as air penetrates the p...

We show that the drying rate of plaster pastes is significantly lower than that expected for a pure liquid evaporating from a simple homogeneous porous medium. This effect is enhanced by the air flow velocity and the initial solid/water ratio. Further tests under various conditions and with the help of additional techniques (MRI, ESEM, Micro-tomogr...

We explore the use of magnetic resonance imaging (MRI) velocimetry and pulsed field gradient nuclear magnetic resonance (PFG NMR) data for studying the flow characteristics of yield stress fluids through model pores (a succession of ducts of different diameters) or real porous media (bead packings). We propose different methods for the quantitative...

From NMR measurements we show that the velocity field of a yield stress fluid flowing through a disordered well-connected porous medium is very close to that for a Newtonian fluid. In particular, it is shown that no arrested regions exist even at very low velocities, for which the solid regime is expected to be dominant. This suggests that these re...

We show that frustrated creep flows of yield stress fluids give rise to a boundary layer, which takes the form of a liquid region of uniform significant thickness separating two solid regions. In this boundary layer the shear rate is approximately constant for a given flow rate and the layer thickness varies extremely slowly with the flow rate.

After drying colloidal particles suspended in a porous medium a concentration gradient appears. Using ^{1}H MRI we propose a protocol to observe simultaneously the distributions of air, liquid, and colloid through the unsaturated solid porous structure. Thus we show that the above phenomenon comes from a receding-front effect: The elements migrate...

The initial part of FID-signals cannot always be acquired experimentally. This is particularly true for signals characterised by strong inhomogeneous broadening, such as those in porous materials, e.g. cements, soils and rocks, those measured by portable NMR-apparatus, or EPR-signals. Here we report on a numerical method we designed to extrapolate...

We measured the pressure drop vs flow rate during the flow, in a wide range of velocities, of well controlled yield stress fluids through confined packings of glass beads of different sizes. A detailed analysis of the data makes it possible to extract a general expression for the pressure drop vs flow rate curve through a porous medium as a functio...

L’agroalimentaire et le génie civil constituent deux domaines d’applications très particuliers pour l’imagerie par résonance magnétique (IRM). Essentiellement axées sur les problèmes d’élaboration, de conditionnement et d’évolution de produits et de matériaux en contexte industriel, les études doivent souvent être menées sur des échantillons massif...

De nombreux systèmes multiphasiques (suspensions de particules colloïdales et non-colloïdales, systèmes polymères, systèmes auto-organisés de tensio-actifs …) sont constitués d’entités qui ont la capacité de s’organiser et de former des structures à différentes échelles. Ces systèmes présentent des comportements rhéologiques complexes qui nécessite...

Food-processing and civil engineering are very particular application fields for magnetic resonance imaging (MRI). Studies mainly focus on preparation, packaging, and further evolution of products and materials in industry. They are often carried out on massive samples. They involve the use of large MRI facilities, and require the development of sp...

Ce travail s'intègre plus largement dans une thématique de l'équipe Imagerie et Matériaux du laboratoire Navier, concernant les matériaux poreux au sens large (matériaux cimentaires, roche, sol, poreux modèles...) et plus précisément le rôle et le déplacement de l'eau dans ces structures complexes. Le spectromètre-imageur est arrivé en 1999, et les...

The internal flow characteristics of a kaolin suspension were examined via magnetic resonance imaging (MRI) in a flow regime for which the material behaves as an almost pure plastic material. The paste also showed a significant tendency toward liquid phase migration under squeezing tests. The MRI measurements produced a 2D slice of the 3D velocity...

We have devised two numerical methods of restoring incomplete band-limited NMR-signals to integrity by either interpolating or extrapolating them. Both methods are based on use of the finite cardinal series, whose filtering properties were discussed previously, to model signals. They require no prior knowledge about the system under study, but only...

We present an interpretation of the self diffusion propagator for a molecular fluid confined in a porous medium. Breaking with conventional routes of interpretation, we focus in reciprocal space on the time dependence of the propagator at a fixed wave vector q. New theoretical results are reported, as well as NMR measurements on a water-saturated p...

The form of the two-dimensional (2D) NMR-relaxation spectra--which allow to study interstitial fluid dynamics in diffusive systems by correlating spin-lattice (T(1)) and spin-spin (T(2)) relaxation times--has given rise to numerous conjectures. Herein we find analytically a number of fundamental structural properties of the spectra: within the eige...

The NMR spectra of porous materials are characterised by broad spectral lines, often due to intrinsic inhomogeneity of their magnetic susceptibility. Another recurrent feature of the spectra is them being a band-limited function. Herein we show that time-domain signals of those systems can be modelled precisely and effectively by finite cardinal se...

Two-dimensional NMR-relaxation spectroscopy, correlating various relaxation mechanisms, proved useful for studies dynamical processes that take place in various porous material [1-5]. Yet development of the Laplace-spectroscopy has been somewhat impeded by difficulties in creating a stable numerical multidimensional Laplace-inversion method free of...

Much has been learnt and speculated about the form of 2D NMR relaxation spectra of diffusive systems. Herein we show that the eigen-modes formalism can help to establish a number of fundamental structural properties, i.e. symmetries, overall intensities, signs and relative intensities of the diagonal and cross components, of such spectra, on which...

We intend to study mechanical effects of freezing and thawing on bulky samples of concrete by nuclear resonance high resolution spectroscopy and imaging (MRI). Variously functionalised three dimensional images of liquid water in the porous media can be obtained by MRI. NMR spectroscopy, on the other hand, can be used to directly measure the total q...

We intend to study mechanical effects of freezing and thawing on bulky samples of concrete by nuclear magnetic resonance (NMR) high resolution spectroscopy and imaging (MRI). Variously functionalised three dimensional images of liquid water in the porous media can be obtained by MRI (see Figure 1). NMR spectroscopy, on the other hand, can be used t...

Nous avons conçu un filtre numérique passe-bas capable de débruiter des signaux RMN tronqués. L'algorithme du filtre consiste à ajuster les données RMN brutes avec une série de sinus cardinaux tronqués. Inspiré de l'approche bayésienne de solution des problèmes inverses, notre filtre requière uniquement que le signal traité soit une fonction à band...

L'extrusion est un procédé industriel permettant de former des objets en poussant à l'aide d'un piston ou d'une ou plusieurs vis un matériau très « pâteux » à travers un petit orifice ou une filière censés lui donner une section de forme particulière. Certaines briques, certaines pièces préfabriquées de matériaux cimentaires, certaines céramiques,...

Extrusion tests were performed by forcing a well-characterized model yield stress fluid from a cylindrical cartridge through various cylindrical extrusion dies using a variety of different piston velocities. In this study the Bingham number within the die ranged from 0.1 to 10. MRI techniques allowed for the non-invasive determination of the local...

The rheology of granular materials near an interface is investigated through proton magnetic resonance imaging. A new cylinder shear apparatus has been inserted in the magnetic resonance imaging device, which allows the control of the radial confining pressure exerted by the outer wall on the grains and the measurement of the torque on the inner sh...

We study the flow of a typical thixotropic material subjected to very different deformation histories (squeeze, shear, and extrusion) with either local (proton NMR and magnetic resonance imaging) or macroscopic measurements after different times of rest. Specifically, we measure the velocity fields and the spin-spin NMR relaxation of the material a...

Digital low pass filters are routinely used to improve the signal-to-noise ratio of NMR signals, e.g. FID or echoes, when pass band widths of the available analogue filters do not correspond to the spectral width of the signals. Applying digital filters will always necessitate an oversampling of the signal to filter. The digital filters with which...

We designed a digital low pass filter suitable for processing truncated NMR signals. In developing our algorithm we were inspired by the Bayesian approach to solving inverse problems. Our method consists in fitting raw NMR data with a finite series of truncated cardinal sine functions and requires nothing but the signal being band-limited. We devis...

The rheology of granular materials near an interface is investigated through proton magnetic resonance imaging. A new cylinder shear apparatus has been inserted in the MRI device, which allows the control of the radial confining pressure exerted by the outer wall on the grains and the measurement of the torque on the inner shearing cylinder. A mult...

NMR signals are unavoidably impaired with noise stemming from the electronic circuits of the spectrometer. This noise is most often white and Gaussian and can be greatly reduced by applying low pass analogue and digital filters. Nevertheless, extra noise with other statistics than Gaussian may interfere with the signal, e.g. when auxiliary electric...

We review and compare the phenomenological aspects and physical origin of shear-localization and shear-banding in various material types, namely emulsions, suspensions, colloids, granular materials and micellar systems. It appears that shear-banding, which must be distinguished from the simple effect of coexisting static-flowing regions in yield st...

Flows of dense emulsions show many complex features among which long range nonlocal effects pose a problem for macroscopic characterization. In order to get around this problem, we study the flows of several dense emulsions, with droplet size ranging from 0.3to40microm , in a wide-gap Couette geometry. We couple macroscopic rheometric experiments a...

We report a 20-MHz proton nuclear magnetic resonance T1 relaxation study of cement paste hydration in the early stages of setting, using different centimeter-sized samples of cements of various origins and different water-to-cement ratios. In every sample, during the first few minutes of hydration, it is found that inverse Laplace processing of inv...

Shear localization is a generic feature of flows in yield stress fluids and soft glassy materials but is incompletely understood. In the classical picture of yield stress fluids, shear banding happens because of a stress heterogeneity. Using recent developments in magnetic resonance imaging velocimetry, we show here for a colloidal gel that even in...

The review deals with applications of magnetic resonance imaging (MRI) techniques to study flow. We first briefly discuss the principles of flow measurement by MRI and give examples of some applications, such as multiphase flows, the MRI rheology of complex fluid flows, and blood flows in the human body.

Synopsis We investigate the flowing behavior of dense suspensions of noncolloidal particles, by coupling macroscopic rheometric experiments and local velocity and concentration measurements through magnetic resonance imaging MRI techniques. We find that the flow is localized at low velocities, and that the material is inhomogeneous; the local laws...

Drag reduction of turbulent flows by surfactant additives is studied. The surfactant forms a shear-induced gel phase in both rheological and turbulent flows. In both flows, the fracture of the gel causes an apparent wall slip. The slipping in turbulent flows decreases the wall friction and therefore immediately leads to drag reduction, providin...

Data processing for NMR velocimetry of fast flow: a numerical study of ‘Couette’ rheo-NMR measurements. NMR velocimetry in Couette rheo-NMR experiments is known to be accurate within the limit that the fluid undergoes small displacements during the sequence. In this work, it is shown that even when this last requirement can not be fulfilled, some g...

From MRI measurements, it is shown that in a flowing cement paste the thixotropic effects dominate over short time scales, while aging effects become significant over larger timescales. The steady state behavior, defined as flow properties in the intermediate period, exhibits a yielding behavior which differs from the prediction of usual yield stre...