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International audience; The phase inversion from a morphology of hydroxypropylcellulose in water (HPC50%) droplets in polydimethylsiloxane (PDMS) matrix to a morphology of PDMS droplets in HPC50% matrix can be induced by a change of shear rate, due to a viscosity ratio inversion. Such a process passing through four different transient morphological stages was studied by optical microscopy in a transparent shear device. In a certain concentration region, at a fixed shear rate, after sheets of PDMS were formed, the transition "hesitates" between phase inversion and refined starting morphology. The influence of PDMS concentration, shear rate, elasticity, and phase dimension on the final morphology was investigated and compared with different models given in the literature. The influence of concentration and shear rate on the duration of the transient flow was also studied. We propose a simplified model of breakage of filaments to explain a part of our results

International audience; The recoil of anisotropic hydroxypropylcellulose solutions was studied by optical microscopy and light scattering. Different stresses were applied before stopping the flow and observing the recoil. At low stress levels, the scaling of the recoverable strain versus scaled relaxation time applies. A change of texture is noticeable only after most of the strain has been recovered. At a high stress level, a band texture appears during recoil. The appearance of this band texture stops the recovery process until the band texture disappears, and the recovery process then continues. The presence of a band texture during recoil is shown to promote a larger recoil.

International audience; The flow of isotropic and liquid-crystalline hydroxypropylcellulose-water solutions is studied in a transparent slit die with several geometries including divergent and convergent configurations. The flow is observed between crossed polars. In addition to the two different flow regimes that are known in shear (zones I and II), a new flow behavior is observed (zone III). Zone I is characterized by a large macroscopic orientation, as seen between crossed polars. It is localized where either shear rates or elongation rates are large. The extinction angle is a function of the position in the die. It is similar to the flow-aligning regime observed at high shear rates. Zone II is much less oriented, due probably to a large density of defects. It is typical of the low shear rate region observed in simple shear. Zone III exhibits a peculiar behavior with long-range orientation instabilities. It is always localized after a diverging zone. Flow around obstacles and colliding streams are also studied.

International audience; A simplified model of the Leslie–Ericksen theory is used to solve the flow of liquid crystalline polymers, seen as viscous anisotropic fluids, making the assumptions of high viscosities and neglecting the director elasticity in the viscosity terms. The resulting equations, known as Ericksen's ‘‘Transversely Isotropic Fluids'' equations involve four rheological parameters. Axisymmetrical isothermal steady flows are considered and the problem is divided into two parts using the method of the fixed point. The velocity calculation is performed by a variational method and a functional minimization technique and the equations are discretized with a finite element method. The director computation is made using a method of characteristics. The results of the computations describe the behavior of anisotropic viscous fluids as a function of flow geometries and rheological coefficients. Complex geometries including converging and diverging channels, expansion and contraction flows, as well as flow around spherical obstacles, are computed. The relative influence of the rheological parameters is also tested.

International audience; We investigated the rheological properties of nanocomposites composed of polypropylene, organoclay, and maleic anhydride grafted polypropylene in small amplitude oscillatory shear. Samples were prepared in two steps: a masterbatch was first obtained by melt extrusion and then diluted into polypropylene using an internal mixer. Three formulations were investigated. The measurement of the storage and loss moduli evolution with time showed that these materials were not stable: the nanostructure obtained after steady shear continuously changed with time, due to the disorientation of the clay platelets and the build-up of a 3D network. The kinetics of the structure build-up (followed via the melt yield stress) showed a two-step process. This feature was found to be valid whatever the nanocomposite formulation. Such evolution of the structure is generally assumed to violate the time-temperature superposition principle. We demonstrate in this paper that the time-temperature equivalence always exists if the same nanostructure is probed. This was achieved by using different annealing times for different temperatures or annealing the samples at the highest temperature before measuring at lower values. The time-temperature equivalence evidences that the temperature does not induce any chemical change within the material, whose properties remain governed by the same physical phenomena.