Rheology of complex fluids and materials

Rheology of complex fluids and materials

Coordinator: Jean-Noël Roux (Laboratoire Navier)

Axis 3 of LABEX MMCD, as opposed to axis 2, is devoted to the rheological behavior of materials in large strain regimes, with possible applications, in particular, to civil engineering and construction materials at elaboration stage (fresh cementitious mixes, gypsum, granular materials…). Those often contain pasty, non-Newtonian fluids and discrete objects or inclusions (grains or bubbles).

Special attention is paid to multiscale approaches apt to capture the physical origin of macroscopic behavior at the level of constitutive elements (grains, colloidal particles…). Complementary knowledge and skills, from the different laboratories and research groups, in the design and processing of well controlled and characterized model materials, in rheometry and visualisation techniques, and in numerical simulation methods at different scales are being used synergistically.

The LABEX support provides decisive impulses to collaborations combining experimental and mathematical tools and modeling schemes developed in various laboratories for the study of the rheology of complex and heterogeneous liquids or soft solids, and strengthens the position of the participating research groups as major actors in this scientific field.

Researches carried out fall into three main themes.

1) Elaboration, characterization and modeling of nanocomposites.

Such materials are made on mixing solid nanoparticles into polyelectrolyte solutions, and then drying.

Effect of temperature on discontinuous shear-thickening of PMAA solution, apparent after some shearing time

These nano composites are used for paintings, insulating layers, and coatings in several industrial fields, including construction. Other composite materials use swollen hydrogels as the continuum phase (in which the hydrosoluble polymer is reticulated), a soft solid retaining a large water content, which is also reinforced by small particle inclusions.

This research includes Clément Robin’s PhD thesis, defended in October, 2016, the postdoc internship of Filippo Ferdeghini (2015-2016), and the ongoing PhD work by Azad Erman.

Supervised by Catherine Amiel, Clémence Le Cœur, and Cédric Lorthioir at ICMPE-SPC and by Guillaume Ovarlez (now working at LOF, Bordeaux) and Abdoulaye Fall at Laboratoire Navier, Clément Robin studied the rheology of polymethacrylic acid (PMAA), and considered different kinds of silica nanoparticles in aqueous dispersion of PMAA with the possibility to trigger polyelectrolyte/silica interactions by varying either the pH or the silica surface functionalization. Polyectrolyte configuration changes caused by shear were also investigated. A variety of techniques were employed to control polymer-silica interactions and monitor microstructures changes under shear (such as small angle X-ray or neutron scattering, possibly under shear flow). Unexpected rheological behaviours in the context of polymer solutions, such as shear thickening, were observed and correlated to microstructure. Tunable silica-polyelectrolyte interactions led to changes in conformations, and of the rheology (measured in the dilute regime).

Small angle X-ray scattering intensity vs. wave vector of two separating phases, in PMAA-silica particle mixture, with evidence of particle aggregation in silica-rich region (blue curve)

Azad Erman’s PhD research, which started in October, 2016, with the same supervisors from ICMPE and Navier laboratories, investigates rheological properties and their relations to microstructure at higher polyelectrolyte concentrations in the presence of the silica filler, and during drying — with the final objective of controlling the mechanical properties of the solid material (Young modulus, strength, aging). For applications to paintings, controlling the rheology (yield stress, thixotropy) in the liquid state is of course another industrial motivation of those studies.

As a postdoctoral research fellow, Filippo Ferdeghini collaborated with the same groups at ICMPE and Laboratoire Navier (where Stéphane Rodts, a specialist of Magnetic Resonance techniques applied to rheometry and to porous media is also involved). He studied hydrogels with platelet-shaped micrometrical solid inclusion highly sensitive to magnetic fields, with the aim of controlling their orientation and its influence on the viscoelastic properties of the composite medium. So far the experimental setup has been designed (enabling the application of a magnetic field to the sample in the rheometer), and appropriate mixtures have been chosen. The effects of magnetic fields and of particle orientations investigated. MRI experiments, coupled to rheometry, have been carried out.

This research benefits from the association, fostered by the LABEX, of physico-chemistry and microstructures characterization techniques available at ICMPE (in group SPC, Systèmes de Polymères Complexes) and of the competence of the Navier group in rheology, rheometry and magnetic resonance imaging.

This collaboration may lead to research proposals submitted to funding agencies such as ANR.

2) Heterogeneous complex fluids

A second set of research projects funded by the LABEX has been dealing with heterogeneous complex fluids, in the presence of interfaces and, especially, bubbles: the design, controlled fabrication and rheological modeling of aerated materials, with applications in civil engineering and construction industries, is a core project of the rheophysics group of Laboratoire Navier. The support of LABEX MMCD fostered collaborations with ESYCOM researchers (particularly in the CMM group—‘Captors and Measurement Microsystems’) who contributed their know-how in the design and fabrication of controlled millifluidic devices and surfaces with preset micrometer scale roughness characteristics. The PhD thesis research carried out by Benoît Laborie, in years 2012-2015, supervised by Élise Lorenceau and Florence Rouyer (Lab. Navier) and by Dan Angelescu (ESYCOM-CMM), led to useful results about the mechanisms by which aerated yield stress fluids (YSF) can be prepared using millifluidic devices (see figure) and the regimes of flow of such bubbly YSF’s in capillary tubes. This work (about which 3 papers are now published in major international journals) paved the way to controlled, stable automated aerated YSF production.

Devices used to form controlled bubble trains within yield stress fluids (YSF) flowing in tube of radios 1mm. T-junction and flow focusing.

Three other PhDs started in October 2015 on related subjects: two experimental ones, by Blandine Feneuil (supervised by Olivier Pitois and Nicolas Roussel, of Laboratoire Navier), and by Xiao Zhang (associating Lab. Navier, with Ph. Coussot and J. Goyon, to ESYCOM, with Philippe Basset) and a computational one, by Karol Cascavita (supervised by Alexandre Ern, of CERMICS, and Xavier Chateau, of Lab. Navier).

X. Zhang’s work ones again exploits the ability of the ESYCOM group to produce elaborate objects with a controlled geometry on a micrometric, or even nanometric scale — in that case, surfaces with specified roughness, grooves, etc… — to carry out innovative flow experiments and rheometric tests with complex fluids. The use of roughness scales varying from manometric (extremely smooth sicicium surfaces) to submillimetric (considerably larger than droplet sizes), in flows of emulsions past solid surfaces, evidenced the gradual disappearance of wall slip for growing roughness, while the wall yield stress increases from zero to the bulk yield stress. Other geometries (small capillaries, elongational flow in squeezed films), and the joint use of rheometry and MRI, allow the PhD student to investigate the applicability of known models in varying situations, testing for possible size effects (not recorded so far), and the appropriate tensorial forms of constitutive laws.

Solidified cement foams that were affected (left column, or not (right column) by drainage; and/or affected (top row) or not (bottom row) by ripening.

While this project tracks basic laws in model systems, Blandine Feneuil’s thesis deals with cementitious materials, with the aim of producing and characterizing aerated cements and concretes. The strong effects on yield stress of the nature and concentration of the surfactant, which interacts with cement grains, was systematically studied. Conditions enabling good control of the possible foam destabilization mechanisms before the hydration reaction solidifies the material (drainage, gas exchange leading t
o ripening, film breakage and coalescence) were identified. Coalescence might be avoided either with a large enough plastic capillary number (involving bubble diameter, yield stress and surface tension), or via a newly identified `granular confinement’ mechanism.

This thesis benefits from the knowledge of cementitious materials developed within IFSTTAR, the civil engineering institute which is one of the parent institutions of Laboratoire Navier (a joint lab with Ecole des Ponts and CNRS). N. Roussel, one of the thesis supervisors, has been working on cement pastes and concretes at IFSTTAR for about 15 years.

Adaptive mesh to simulate Poiseuille flow of yield stress fluid in a tube, apt to capture boundary of solid plug.

The work of PhD student Karol Cascavita Mellado is being carried out within CERMICS, the applied maths unit at École des Ponts (with Alexandre Ern), in contact with the rheophysics group at Lab. Navier (X. Chateau). The aim of this research is to apply innovative numerical methods, known as Hybrid High Order (HHO), to the numerical modelling of non-Newtonian (e.g., Bingham, Herschel-Bulkley) fluid flows, ultimately with inclusions of bubbles. HHO methods (which use face-based discrete unknowns), and conical projection algorithms (developed by J. Bleyer in another Navier lab. group), to be also tested, are promising candidates to overcome the known numerical difficulties associated with non-Newtonian liquid modeling, especially in the presence of interfaces. Karol Cascavita first developed codes to deal with simpler cases (2D Newtonian liquids, steady Bingham flow, Poiseuille problem…), but with suitably adaptive meshes capturing transition boundaries (between sheared regions and solid plugs in the center of a tube, or dead zones in the corners) with good control of geometric accuracy.

3) Particle-scale structure and dynamics of colloidal suspensions

Finally, a third set of LABEX-funded projects, (collectively defined as a ‘transverse projet’ within the new LABEX organization) with one PhD thesis and two postdoctoral positions, is currently inevstigating particle-scale structure and dynamics of colloidal suspensions. An original combination of optical tools designed within ESYCOM, and microscopy and rheometry techniques used in Laboratoire Navier, will be applied to correlate microstructure and rheology, and, also, to better characterize particles interactions. Molecular dynamics simulations will be carried out in parallel with the experiments.

Silica beads (diameter = 1μm)

Stress-strain curves of suspension after different aging times

PhD student Francesco Bonacci has been characterizing the microstructure and rheology of silica suspensions, combining geometry with observations by confocal microscopy. A collaboration with Eric Furst (University of Delaware) has been set up to directly investigate the interaction of those particles with means of optical tweezers.

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