Albert Magnin

Centre National de la Recherche Scientifique / French National Centre for Scientific Research, Laboratoire Rhéologie et Procédés, Undergraduate

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Weixiang Sun

South China University of Technology

PROF. OM PRAKASH SINHA

Amity University

David Seamon

Kansas State University

Benjamin Wilson

Aalto University

Amir Khamsehnezhad

TWI Ltd

Prof.Dr. İbrahim USLU

Gazi University

Kenneth Vecchio

University of California, San Diego

Bryan M Wong

University of California, Riverside

jafar hasnain

The Islamia University of Bahawalpur

Kiran Dasari

University of Illinois at Urbana-Champaign

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Papers by Albert Magnin

Aluminia interaction with AMPS-MPEG random copolymers III. Effect of FEG segment legnth on adsorption, electrokinetic and rheological behaviour

Etudes expérimentales et numériques de l’écoulement d’un fluide à seuil autour d’un cylindre

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Rhéologie En Cisaillement Et Compression De Dispersions Aqueuses D'Une Argile Modèle Dans Le Régime Concentré

18 ?me Congr?s Fran?ais de M?canique Grenoble, 27-31 ao?t 2007 1 Rh?ologie en cisaillement et com... more

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Published by the The Society of Rheology

We propose a microscopic framework based on nonequilibrium statistical mechanics to connect the m... more We propose a microscopic framework based on nonequilibrium statistical mechanics to connect the microscopic level of particle self-assembly with the macroscopic rheology of colloidal gelation. The method is based on the master kinetic equations for the time evolution of the colloidal cluster size distribution, from which the relaxation time spectrum during the gelation process can be extracted. The relaxation spectrum is a simple stretched-exponential for irreversible diffusion-limited colloidal aggregation gelation, with a stretching exponent d f /3, where d f is the mass fractal dimension. As opposed to glassy systems, the stretched-exponential relaxation does not result from quenched disorder in the relaxation times, but from the selfassembly kinetics in combination with the fractal character of the process. As the master kinetic equations for colloidal aggregation do not admit bond-percolation solutions, the arrest mechanism is driven by the interconnection among fractal clusters when excluded volume becomes active, i.e., at sufficiently high packing of clusters. The interconnections between rigid clusters decrease the soft modes of the system and drive a rigidity-percolation transition at the cluster level. Using the Boltzmann superposition principle, the creep and the full rheological response can be extracted for both irreversible and thermoreversible colloidal aggregation. In the case of thermoreversible gelation, the attraction energy is finite and plays the role of the control parameter driving a nonequilibrium phase transition into a nonequilibrium steady-state (the gel). A power-law spectrum coexisting with a stretched-exponential cut-off is predicted leading to power-law rheology at sufficiently high frequency. Our theory is in good agreement with experimental data of different systems published by other authors, for which no theory was available. V

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Mécanismes et cinétiques d'adhésion aux échelles microniques de levures Saccharomyces cerevisiae sur du verre, quantification des forces d'interactions

In-situ Structural Characterization by SAXS and Flow Properties of Colloidal Suspensions During Cross-flow Ultrafiltration

AIP Conference Proceedings, 2008

The flow properties and induced structures during concentration of colloids near the membrane in ... more The flow properties and induced structures during concentration of colloids near the membrane in ultrafiltration processes where studied on the base of new techniques developed at the ``Laboratoire de Rhéologie&amp;amp;amp;amp;#39;&amp;amp;amp;amp;#39;. The use of a specific cross-flow ultrafiltration cell combined with in-situ time resolved small angle x-ray scattering (SAXS) allowed to access the pertinent length scales of the filtered colloids. Anisotropic

A new way to apply ultrasound in cross-flow ultrafiltration: Application to colloidal suspensions

Ultrasonics Sonochemistry, 2014

A new coupling of ultrasound device with membrane process has been developed in order to enhance ... more A new coupling of ultrasound device with membrane process has been developed in order to enhance cross-flow ultrafiltration of colloidal suspensions usually involved in several industrial applications included bio and agro industries, water and sludge treatment. In order to reduce mass transfer resistances induced by fouling and concentration polarization, which both are main limitations in membrane separation process continuous ultrasound is applied with the help of a vibrating blade (20 kHz) located in the feed channel all over the membrane surface (8 mm between membrane surface and the blade). Hydrodynamic aspects were also taking into account by the control of the rectangular geometry of the feed channel. Three colloidal suspensions with different kinds of colloidal interaction (attractive, repulsive) were chosen to evaluate the effect of their physico-chemical properties on the filtration. For a 90 W power (20.5 W cm À2) and a continuous flow rate, permeation fluxes are increased for each studied colloidal suspension, without damaging the membrane. The results show that the flux increase depends on the initial structural properties of filtered dispersion in terms of colloidal interaction and spatial organizations. For instance, a Montmorillonite Wyoming-Na clay suspension was filtered at 1.5 Â 10 5 Pa transmembrane pressure. Its permeation flux is increased by a factor 7.1, from 13.6 L m À2 h À1 without ultrasound to 97 L m À2 h À1 with ultrasound.

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Structure under shear flow of thixotropic clay gels

ABSTRACT The thixotropic behavior of colloidal clay dispersions consisting of disc-shaped particl... more ABSTRACT The thixotropic behavior of colloidal clay dispersions consisting of disc-shaped particles of nanometric size, was studied by using a combination of SAXS, SANS and SLS techniques and rheometric measurements. The aim here is to examine the influence of shear flow on structural changes at various length scales, involved in the thixotropic behavior, and link these with their macroscopic mechanical properties. At rest, the structure of the dispersions is composed of subunits measuring a few tens of nanometers that combine to form dense aggregates measuring about a micrometer. At larger length scales, these micrometer-sized aggregates are rearranged to form a continuous 3-dimensional isotropic structure that has a fractal behavior of dimension D, which gives the gels their texture. The gel state is reached above a volume fraction fv*, for a given ionic strength and gelation time. The influence of the volume fraction on the structure was correlated with the yield stress and the fractal dimension by means of a scaling law (Pignon et al. 1996 ; 1997 a).

Structure of nano-composite (fibers-PEO) materials in extensional Flow

ABSTRACT Extensive researches on nano-composite materials submitted to shear flow or extensional ... more ABSTRACT Extensive researches on nano-composite materials submitted to shear flow or extensional flow, have been motivated by their spectacular rheological behavior and vast industrial applications (deposition, ultrafiltration, extrusion, etc.). Indeed, these materials under extensional flow can exhibit time dependent viscoelastic properties. Instabilities such as localization, phase separation, segregation, can occur which are not well understood. The scientific objective of this research is to elucidate the relationship between the extensional flow properties (strain and stress fields) and the dynamics of the induced structures (orientation, aggregation, phase transition, etc.). The nano-composite materials studied are composed of sepiolite clay particles (rigid rods 1 micrometer long and 0.010 micrometers in diameter) in a water-soluble polymer, polyethylene oxide. The trajectory of the strain field within the sample volume has been well characterized by particle imaging velocimetry, in order to apply pure extensional flows in the desired extensional rate and viscosity domains. A new extensional flow device developed at the &quot;Laboratoire de Rhéologie&quot;, has allowed to combine extensional flow with SAXS on ID02 at the ESRF. Time-resolved information has been obtained on the orientation dynamics of the fibers in the polymer matrix. Analysis of extensional transient and steady state regimes revealed the main characteristics of the extensional flow of these nano-composite suspensions. Under steady states, the fibers are aligned along the extensional direction. The evolution of the orientation order parameter versus strain rate has allowed defining the rate of organization of the fibers at increasing extensional flow rates. Under transient states, time evolution of the order parameter permitted to identify the time scales at which the fibers get aligned in the extensional field and the time scales over they relax in the polymer matrix.

Structure et rhéologie de suspensions thixotropes d'argile

La structure au repos et les proprietes rheologiques d'une suspension colloidale thixotrope d... more La structure au repos et les proprietes rheologiques d'une suspension colloidale thixotrope d'argile, ont ete etudiees par la combinaison de mesures angulaires de diffusions de differents rayonnements et par des mesures rheometriques. L'echelle de longueur de l'ordre du micron a ete identifiee comme etant celle qui est principalement responsable des comportements macroscopiques observes dans cette suspension. Cette echelle de longueur est liee a une dimension fractale qui passe de 1 a 1,8 au voisinage d'une concentration critique. Une loi d'echelle a permis de correler ces dimensions fractales a l'influence de la fraction volumique sur la contrainte seuil. Quatre regimes ont ete definis dans la courbe d'ecoulement qui est a minimum de contrainte : deux regimes montrant des instabilites d'ecoulement comme la localisation du cisaillement et deux regimes mettant en jeu des proprietes de volume de l'echantillon. En consequence, des procedures pour la caracterisation de la thixotropie des suspensions sont proposees.

Structure of skimmed milk ultrafiltration process probed by in-situ small angle X-ray scattering. Poster

In-situ characterization of anisotropic colloids deposition by SAXS during crossflow ultrafiltration

International audienceThe membrane separation processes are commonly used for concentrating and p... more International audienceThe membrane separation processes are commonly used for concentrating and purifying colloidal dispersions in industry. The main limitation of this process is the accumulation of matter in the neighborhood of the membrane surface. The concentration polarization and/or deposit formation related to this accumulation of matter are the dominant causes of flux decline and control the filtration performance. Consequently there is tremendous interest in understanding mechanisms involved in the structural evolutions of the polarization layer at the colloidal length scales. It would allow devising appropriate steps to reduce the structuring effect. During the past decade few studies [1] have been focused on in-situ monitoring techniques to observe the concentration polarization and fouling phenomena. The focus of this work is in-situ characterization of the induced structures of colloidal dispersions in the vicinity of the ultrafiltration membranes, when they are simultaneously subjected to transmembrane pressure and tangential flow. To fulfill this challenge a new tangential ultrafiltration SAXS cell has been developed at the "Laboratoire de Rhéologie". This cell has allowed to combine SAXS at the European Synchrotron Radiation Facility (ID02 beamline) with membrane separation (Fig. 1). It has been performed under various crossflow and permeation conditions. The high beam collimation provided by the modern synchrotron source makes x-ray scattering an ideal tool for this work [2]. Systems studied are anisotropic colloidal aqueous dispersions composed of sepiolite rods 1 micrometer long and 0.01 micrometers in diameter, a natural non-swelling fibrous clay from Vallescas, Spain. The initial concentration of the filtered suspensions C0 = 0.01 g/ml (0.5 vol%), is in the semi-dilute domain for which the suspensions exhibit a shear thinning rheological behavior. The tangential ultrafiltration SAXS cell used in these measurements contained a flat polysulfone ultrafiltration membrane (100 kD). During filtration, a transmembrane pressure P = 1.105 Pa is applied and successives tangential flows Q were imposed. The permeation flux J is continuously measured and simultaneously the x-ray beam (40 x 250 micrometer) crossed the lateral dimension of the cell to probe the structure of the concentration polarization layer during time t at different heights z above the membrane (Figs. 1 and 2). As already described in previous studies concerning frontal filtration mode [3-4], a calibration curve relating the absolute scattering intensity to the particles concentration has allowed to deduce the concentration profile as a function of the distance z to the membrane. In Fig. 2, a transmembrane pressure of 1.105 Pa was applied at t = 12 min. The lower retentate tangential flow Q (0.03 L/min) beginning t = 24 min initiated the growth of the deposit layer. With successive higher applied Q, a continuous increase in thickness, anisotropy and concentration of the deposit layer was observed with a simultaneously gradual decrease of the permeation flux with time. The high level of concentration reached in the deposit, up to 50 times the initial concentration, and the highly anisotropic structure formed, would certainly play a decisive role in the mechanisms which control the filtration performance of the sepiolite dispersions. The success of these first measurements on a well known colloidal system open new tremendous opportunities to study in-situ the mechanisms occurring in cross flow filtration. It would bring essential experimental data necessary for improvement in theoretical and numerical modelling. Fig. 2: Permeation flux J(t), concentration profile and SAXS pattern versus time and distance z to the membrane, deduced from in-situ SAXS during ultrafiltration of sepiolite suspensions at initial concentration C0 = 0.01 g/ml, for various pressure and cross flow conditions. Keywords: colloid, anisotropic, crossflow ultrafiltration, deposition, structure, small-angle x-ray scattering. [1] J.C. Chen, Q. Li, and M. Elimelech, Adv. Colloid Interface Sci., 107, 83 (2004). [2] T. Narayanan, O. Diat, and P. Bosecke, Nucl. Instrum. Meth. A, 467, 1005 (2001). [3] F. Pignon, A. Alemdar, A. Magnin, and T. Narayanan, Langmuir, 19, 8638 (2003). [4] F. Pignon, G. Belina, T. Narayanan, X. Paubel, A. Magnin and G. Gésan-Guiziou, Journal of Chemical Physics, 121(16), 8138 (2004)

Structure of skimmed milk during ultrafiltration process probed by in-situ small angle X-ray scattering

The stability and mechanism underlying the formation of deposits of casein micelles during ultraf... more The stability and mechanism underlying the formation of deposits of casein micelles during ultrafiltration process were investigated by small-angle and ultra small-angle X-ray scattering (SAXS and USAXS). The casein micelle dispersions consisted of phospho-caseinate model powders and fresh skimmed milk and the measurements probed length scales ranging from 1 to 2000 nm. Rheometric and frontal filtration measurements were combined with SAXS to establish the relationship between the rheological behavior of deposits (shear and/or compression) and the corresponding microstructure. The results obtained clearly demonstrate that the equilibrium structure of casein micelles is globular with a radius of gyration (R g ~ 100 nm). The internal structure of the micelles is more likely an unfolded state of the constituent proteins rather than globular sub-micelles (Fig. 2). In-situ ultrafiltration experiments under SAXS relate the reduction in the filtration rate to the evolution of microstructure near the membrane. The specific resistance shows a quick linear increase before slowing down. Correspondingly, the scattering pattern in the close vicinity of the membrane becomes anisotropic for long times filtration (Fig. 1) indicating the deformation of the globular micelles. From absolute SAXS intensities, the concentration of the micelles in the deposit can be deduced reliably (Fig. 3).

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Processus de désagrégation dans des gels d'argile thixotopes sous écoulement de cisaillement

Le comportement sous cisaillement d'un gel thixotrope d'argile a ete etudie par la combin... more Le comportement sous cisaillement d'un gel thixotrope d'argile a ete etudie par la combinaison de mesures de diffusion de lumiere statique et de mesures rheometriques. Au repos, la structure du gel est composee d'agregats microniques denses associes en une masse fractale. Sous cisaillement, une figure de diffusion en forme de papillon a ete observee. Elle est attribuee a une contraction et un etirement des agregats microniques perpendiculairement a la direction de la vitesse de cisaillement. L'influence du gradient de vitesse sur ce processus de desagregation a ete etudie et relie aux mesures rheometriques.

Rhéométrie et structure de dispersions de silices nanométriques dans du polyol

Dans cet article, les propriétés rhéologiques d'un système composé de polyol et de silice sont ét... more Dans cet article, les propriétés rhéologiques d'un système composé de polyol et de silice sont étudiées. Trois silices de taille nanométriques avec des surfaces hydrophiles et hydrophobes ont été étudiées. Les mesures rhéométriques ont montré que les dispersions de silices hydrophobes, possèdent des seuils d'écoulement contrairement à la silice hydrophile. Nous avons quantifié le comportement plastique des dispersions de silice hydrophobe par un seuil d'écoulement σ 0 et par un module élastique G'. Il s'avère que ces paramètres suivent des lois d'échelle en fonction de la fraction volumique de silice introduite de la forme : σ 0 ~ φ v 2,9±0,2 , G' ~ φ v 4,1±0,3. Les mesures en diffusion de rayonnement (SLS, SANS) montrent un agencement fractal (D= 1,8) de la structure sur des échelles de longueur allant de la particule élémentaire de quelques nanomètres jusqu'à des agrégats de quelques micromètres. Nous avons établi des corrélations entre les lois d'échelles théoriques et des lois d'échelle expérimentales déterminées par nos mesures rhéométriques.

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Stabilité, Structure et Propriétés Mécaniques de Mousses Polyuréthane chargées

ABSTRACT Dans le domaine des mousses composites, l’ajout de renfort dans la matrice polymère a de... more ABSTRACT Dans le domaine des mousses composites, l’ajout de renfort dans la matrice polymère a de nombreuses conséquences aussi bien sur la formulation que sur les propriétés mécaniques et de structure de ces matériaux alvéolaires. Des mousses polyuréthane composites, formulées à partir de suspensions constituées de carbonate de calcium (CaCO3) et de silice colloïdale (SC), ont été étudiées. Le but de ce travail a été d&#39;explorer d&#39;une part l&#39;influence des fractions volumiques en charge minérales (φcc) et colloïdales (φsc) sur les propriétés rhéométriques et sur la stabilité des mélanges avant moussage. D’autre part, ce travail traite de l’influence du renforcement sur les propriétés mécaniques et sur la structure des mousses solides. Pour les suspensions sans silice colloïdale, un seuil d’écoulement et une période de stabilité sont détectés pour une fraction volumique au delà d’environ 28,2% en CaCO3. Une concentration optimale en CaCO3 a été déterminée (φcc = 46,2%) du point de vue de la mise en oeuvre et de la stabilité. A cette concentration optimale, les propriétés mécaniques (modules élastiques, contrainte de début de plateau) des mousses polyuréthane correspondantes ont été déterminées et correctement prédites par le modèle 2+1 phases de Christensen et Lo (1979). L’ajout de silice colloïdale dans les suspensions entraîne l’augmentation du seuil d’écoulement et de la stabilité, mais ne modifie pas les propriétés mécaniques des mousses.

Compressive rheology of colloidal gels of anisotropic caly particles

ABSTRACT

Structure and orientation dynamics of sepiolite fibers–poly(ethylene oxide) aqueous suspensions under extensional and shear flow, probed by in situ SAXS

Rheologica Acta, 2009

The structure and orientation dynamics of sepiolite clay fibers about 1,000 nm long and 10 nm thi... more The structure and orientation dynamics of sepiolite clay fibers about 1,000 nm long and 10 nm thick, suspended in an aqueous poly(ehtylene oxide) matrix of 10 5 g/mol molecular mass, have been studied under control extensional and shear flow. A new extensional flow cell developed at the "Laboratoire de Rhéologie" and the combined rheology and small angle X-ray scattering (Rheo-SAXS) setup available at the European Synchrotron Radiation Facility have allowed access to in situ and time-resolved fiber orientations and structure properties in the volume of suspensions under flow. In the volume fractions and shear rate domains for which the suspensions exhibit shear-thinning properties, two regimes of orientation separated by a critical strain rate have been identified under extensional flow.

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Spatial and Temporal in Situ Evolution of the Concentration Profile during Casein Micelle Ultrafiltration Probed by Small-Angle X-ray Scattering

Langmuir, 2008

Understanding the mechanisms involved in structural development in the vicinity of membrane const... more Understanding the mechanisms involved in structural development in the vicinity of membrane constitutes a considerable challenge in the improvement of ultrafiltration process in industrial applications. In situ small-angle X-ray scattering (SAXS) performed with custom-made ultrafiltration cell has permitted the structural arrangement to be probed and concentration profiles to be obtained in deposited layers during frontal filtration of casein micelle suspension. SAXS allowed the structure of the accumulated layers of casein micelles between 280 µm and 1 mm from the membrane surface to be followed at length scales from a few nanometers to about 100 nm. These results have been combined with hydrodynamic measurements (permeation flux) and rheological investigations. Under frontal filtration, the time dependence of concentration at different distances from the membrane surface has been obtained. This temporal evolution is marked by an exponential increase of the concentration followed by a slower growth which has been associated with a change in the rheological behavior of the suspension from Newtonian to shear thinning behavior.

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Osmotic Compression and Expansion of Highly Ordered Clay Dispersions

Langmuir, 2006

Aqueous dispersions of nanometric clay platelets (Laponite ®) have been dewatered through differe... more Aqueous dispersions of nanometric clay platelets (Laponite ®) have been dewatered through different techniques: centrifugation, mechanical compression, and osmotic stress (dialysis against a polymer solution). The positional and orientational correlations of the particles have been determined through Small Angle Neutron Scattering. Uniaxial compression experiments produce concentrated dispersions (volume fraction > 0.03) in which the platelets have strong orientational and positional correlations. The orientational correlations cause the platelets to align with their normal along a common axis, which is the axis of compression. The positional correlations cause the platelets to be regularly spaced along this direction, with a spacing that matches the average volume per particle in the dispersion. The swelling law (volume fraction vs. separation) is onedimensional, as in a layered system. Changes in the applied osmotic pressure cause the water content of the dispersion to either rise or decrease, with time scales that are controlled by interparticle friction forces and by hydrodynamic drag. At long times, the dispersions approach osmotic equilibrium, which can be defined as the common limit of swelling and deswelling processes. The variation of the equilibrium water content with the applied osmotic pressure has been determined over one decade in volume fractions (0.03 < φ < 0.3) and 3 decades in pressures. This equation of state matches the predictions made from the knowledge of the forces and thermal agitation for all components in the dispersion (particles, ions and water).

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Aluminia interaction with AMPS-MPEG random copolymers III. Effect of FEG segment legnth on adsorption, electrokinetic and rheological behaviour

Etudes expérimentales et numériques de l’écoulement d’un fluide à seuil autour d’un cylindre

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Rhéologie En Cisaillement Et Compression De Dispersions Aqueuses D'Une Argile Modèle Dans Le Régime Concentré

18 ?me Congr?s Fran?ais de M?canique Grenoble, 27-31 ao?t 2007 1 Rh?ologie en cisaillement et com... more

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Published by the The Society of Rheology

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Mécanismes et cinétiques d'adhésion aux échelles microniques de levures Saccharomyces cerevisiae sur du verre, quantification des forces d'interactions

In-situ Structural Characterization by SAXS and Flow Properties of Colloidal Suspensions During Cross-flow Ultrafiltration

AIP Conference Proceedings, 2008