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Bel Haaj S.,University of Sfax | Magnin A.,CNRS Rheology Laboratory | Petrier C.,CNRS Rheology Laboratory | Boufi S.,University of Sfax
Carbohydrate Polymers | Year: 2013

Nano-sized starch particles (NSP) were prepared from starch granules using a purely physical method of high-intensity ultrasonication. Particle size distribution, Field Effect Scanning Electron Microscopy (FE-SEM), Raman spectroscopy, and Wide-Angle X-ray Diffraction (WAXD) were used to characterize the morphology and crystal structure of the ensuing nanoparticles. The results revealed that ultrasound treatment of the starch suspension in water and at low temperature for 75 min results in the formation of starch nanoparticles between 30 and 100 nm in size. An attempt to explain the generation of starch nanoparticles was made on the basis of WAXD, Raman analysis and FE-SEM observation. Compared to acid hydrolysis, which is the most commonly adopted process, the present approach has the advantage of being quite rapid, presenting a higher yield and not requiring any chemical treatment. © 2012 Elsevier Ltd.

Mabrouk A.B.,University of Sfax | Magnin A.,CNRS Rheology Laboratory | Belgacem M.N.,CNRS Structural Engineering | Boufi S.,University of Sfax
Composites Science and Technology | Year: 2011

Nanocomposites based on poly(styrene-co-hexylacrylate) copolymer and cellulose whiskers as the nanosize filler were prepared by in situ miniemulsion polymerization and their melt rheological behaviours were investigated under dynamic shear conditions. The effects of γ-methacryloxypropyl triethoxysilane (MPS) content along with the whisker loading were explored. In the absence of whiskers, a transition from a liquid- to a solid-like behaviour was observed when the polymer was synthesized in the presence of MPS. When cellulose nanofiller was added, the storage modulus G' and the dynamic viscosities η of the nanocomposites increased monotonically with whisker content and the resulting materials displayed a solid-like behaviour. Above 2. wt.%. loading, a percolated interconnected whisker-whisker network is built up, producing a jump in the storage modulus and strong shear-thinning behaviour of the viscosity. However, as the nanocomposites were prepared in the presence of 3% of MPS, no enhancement nor in the storage modulus nor in the viscosity was observed up to 5. wt.%. of whisker loading. Such a phenomenon was ascribed to inhibition of build-up of the whisker network. The non-linear viscoelastic behaviour of the nanocomposites was also investigated and analysed in terms of the breakdown of different networks, namely the filler-filler and the polymer-filler networks. © 2011 Elsevier Ltd.

Chinesta F.,University of Nantes | Ammar A.,CNRS Rheology Laboratory | Cueto E.,University of Zaragoza
International Journal for Numerical Methods in Engineering | Year: 2010

In this paper the coupling of a parabolic model with a system of local kinetic equations is analyzed. A space-time separated representation is proposed for the global model (this is simply the radial approximation proposed by Pierre Ladeveze in the LATIN framework (Non-linear Computational Structural Mechanics. Springer: New York, 1999)). The originality of the present work concerns the treatment of the local problem, that is first globalized (in space and time) and then fully globalized by introducing a new coordinate related to the different species involved in the kinetic model. Thanks to the non-incremental nature of both discrete descriptions (the local and the global one) the coupling is quite simple and no special difficulties are encountered by using heterogeneous time integrations. © 2009 John Wiley & Sons, Ltd.

Gonzalez D.,Aragon Institute of Engineering Research | Ammar A.,CNRS Rheology Laboratory | Chinesta F.,École Centrale Nantes | Cueto E.,Aragon Institute of Engineering Research
International Journal for Numerical Methods in Engineering | Year: 2010

Separated representations based on finite sum decompositions constitute an appealing strategy for reducing the computer resources and the calculation costs by reducing drastically the number of degrees of freedom that the functional approximations involve (the number of degrees of freedom scale linearly with the dimension of the space in which the model is defined instead of the exponential growing characteristic of mesh-based discretization strategies). In our knowledge the use of separated representations is the only possibility for circumventing the terrific curse of dimensionality related to some highly multidimensional models involving hundreds of dimensions, as we proved in some of our former works. Its application is not restricted to multidimensional models, obviously separated representation can also be applied in standard 2D or 3D models, allowing for high resolution computations. Because its early life numerous issues persist, many of them attracting the curiosity of many research groups within the computational mechanics community. In this paper we are focusing in two issues never until now addressed: (i) the imposition of non-homogenous essential boundary conditions and (ii) the consideration of complex geometries. © 2009 John Wiley & Sons, Ltd.

Mougin N.,CNRS Rheology Laboratory | Magnin A.,CNRS Rheology Laboratory | Piau J.-M.,CNRS Rheology Laboratory
Journal of Non-Newtonian Fluid Mechanics | Year: 2012

The shape and trajectory of bubbles in Carbopol gels were accurately observed over long periods. As the concentration increases, the trajectories are observed to evolve from vertical and rectilinear to three-dimensional shapes. Local strain and velocity fields have been determined. Bubble injection is quasi-static in order to obtain a separation governed by the equilibrium among surface tension, buoyancy and stresses applied to the bubble. Internal stresses in the fluid, of structural origin and induced by the mechanical history in the fluid volume, remain in the fluid for at least several months. They play a major role in bubble formation and propagation. © 2012 Elsevier B.V.

Metivier C.,CNRS Rheology Laboratory | Magnin A.,CNRS Rheology Laboratory
Journal of Non-Newtonian Fluid Mechanics | Year: 2011

This work investigates the effect of wall slip on the stability of the Bingham Rayleigh-Bénard Poiseuille flow. The steady state of the Bingham plane Poiseuille flow is characterized by an unyielded region of 2yb width and two sheared regions close to the walls with both no-slip and slip conditions at the walls. A linear stability analysis of this flow with slip conditions is proposed in this paper. The slip boundary conditions case leads to flow destabilization compared with the results obtained in the no-slip case. Critical conditions are modified by varying Cf, the friction number. For Cf30 the flow is stabilized, i.e. Rac values increase and finally tend to that of the no-slip case when Cf>1000. Furthermore, for 1

Mariano M.,Grenoble Institute of Technology | Mariano M.,CNRS Rheology Laboratory | El Kissi N.,CNRS Rheology Laboratory | Dufresne A.,Grenoble Institute of Technology
Journal of Polymer Science, Part B: Polymer Physics | Year: 2014

Cellulosic nanoparticles with high Young's modulus, crystallinity, specific surface area, and aspect ratio can be found in the natural structure of plant fibers. Indeed, lignocellulosic fibers consist of semicrystalline cellulose nanofibrils embedded in an amorphous matrix mainly composed of lignin and hemicelluloses. These nanostructures give the mechanical strength to higher plant cells, and are biodegradable, renewable, resistant, and widely available to produce nanocomposites with low density, and improved and controlled mechanical, optical, and barrier properties. Nanoparticles can be extracted from cellulose using a top-down mechanically or chemically assisted deconstructing strategy, and owing to their highly reactive surface ensuing nanomaterials can be chemically modified to tailor their properties for a wide range of applications. This review is limited to cellulose chemically extracted nanocrystals and aims to provide an overview about several aspects that involve this material, including sources, properties, challenges, and perspectives. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 791-806 Impressive mechanical properties and reinforcing capability, abundance, low weight, renewability, and biodegradability make cellulose nanocrystals ideal candidates for use in polymer nanocomposites. This Review also looks at the broad range of potential applications of these nanoparticles, as well as the remaining questions in the field. © 2014 Wiley Periodicals, Inc.

Ahonguio F.,CNRS Rheology Laboratory | Jossic L.,CNRS Rheology Laboratory | Magnin A.,CNRS Rheology Laboratory
Journal of Non-Newtonian Fluid Mechanics | Year: 2014

This experimental analysis addresses the non-inertial flow of a yield stress fluid around spheres. The analysis was conducted for two spheres with different surface conditions. Friction laws at their interface have been determined. For the bulk behaviour of the fluid, elastoviscoplasticity and viscoelasticity have also been characterised. The resulting parameters have been used to analyse the experimental results. The drag coefficient was determined with respect to hydrophobic properties and surface roughness. From this determination, a criterion enabling the prediction of a sphere's stability in a yield stress fluid as a function of the fluid/sphere interfacial properties has been proposed. The kinematic fields have also been measured by PIV. These fields enable the quantification of the velocity fields around the spheres according to the adherence conditions of the fluid. This quantification has enabled the characterisation of the extent and the shape of sheared and static rigid zones. Moreover, the calculations of the drag force due to the shear stresses and the drag force due to the normal stresses have revealed the preponderance of the latter in the total drag force. © 2014 Elsevier B.V.

Rharbi Y.,CNRS Rheology Laboratory
Macromolecules | Year: 2012

Amphiphilic block copolymers autoassemble in water to form either dynamically active micelles or frozen particles at high surface tension. The dynamics of these systems is dominated by an individual process, which involves insertion-expulsion of copolymer chains, and a collective one, which involves fusion and fragmentation of proper micelles. The details of these mechanisms can drastically affect the micelles' morphology and some of their applications (drug delivery, template for mesoscopic structures, etc.). While fusion and fragmentation were found to be important in out-of-equilibrium kinetics such as sphere-to-rod transition, they were reported to be irrelevant at equilibrium by both theories and chain randomization experiments. We show, for the first time, that fusion and fragmentation do in fact take place at equilibrium in triblock copolymer micelles poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide). This was achieved using a fluorescent technique, which probes the randomization of hydrophobic pyrene derivatives between micelles. © 2012 American Chemical Society.

Mossaz S.,CNRS Rheology Laboratory | Jay P.,CNRS Rheology Laboratory | Magnin A.,CNRS Rheology Laboratory
Journal of Non-Newtonian Fluid Mechanics | Year: 2010

The appearance of a recirculation zone and the formation of non-stationary vortices behind a cylinder in the unconfined flow of a Herschel-Bulkley fluid have been studied by numerical simulation. The Herschel-Bulkley constitutive equation was regularised by using the Papanastasiou model. Special attention was paid to determining the numerical parameters and comparing them to existing results. The influence of the Oldroyd number and power-law index on flow morphology and, in particular, on the unyielded zones was studied over a wide spectrum (0 ≤ Od≤ 10) and (0.3 ≤ n≤ 1.8). It was seen that the greater the Oldroyd number, the greater the critical Reynolds numbers and Strouhal number for the two flow regimes. The influence of the power-law index is more complex. © 2010 Elsevier B.V.

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