Biomedical subjects

L Talini

Publications and source records attributed to L Talini.

5 recordsLinked to original sources

PubMed2005

Structuring sedimentation in a shear-thinning fluid.

We study the sedimentation of suspensions of monodisperse non-Brownian particles in a shear-thinning polymeric fluid. We observe the formation of particle-rich structures and show that they are associated with a well-defined flow pattern. The results suggest that the observed structuring is a consequence of particle aggregation that amplifies concentration heterogeneities, the flow pattern being further driven by a gravitational instability.

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PubMed2003

Rapid settling of a colloidal gel.

We study the rapid collapse of gels formed from strongly aggregating colloidal suspensions. This gravity-driven collapse is associated with the apparition of fractures in the bulk of the gels that provide an easy route to the gel-supernatant interface for the solvent and are the cause for the strong increase of the settling velocity. We propose a model that connects the apparition of a fracture in the gel to the settling velocity of the interface. This description takes into account the microscopic structure of the gel and is consistent with the experimental results.

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PubMed2002

Rectified motion of colloids in asymmetrically structured channels.

We set micron size particles into macroscopic motion by submitting them to a low frequency electric field (of zero mean value) in a microfabricated channel exhibiting a topological ratchet-like local polarity. Rectification is induced by the coupling between electrophoresis, electroosmosis, and dielectrophoresis. The macroscopic velocities of the particles are functions of the electric field and of the geometry of the channel; they strongly depend on their size which opens the way to potential separations.

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PubMed2002

Aggregation of particles settling in shear-thinning fluids. Part 2. Three-particle aggregation.

We have experimentally studied the coaxial settling of three identical non-Brownian spheres in a shear-thinning fluid at small Reynolds numbers. While settling, the particles create corridors of reduced viscosity in their wake and, if they are initially close enough to one another, they can form stable clusters. By analogy with previous results obtained on two-particle interaction in the first part of this work, we show that the particle velocities can be satisfactorily described using a first-order expression and assuming that the reduced viscosity remains constant. We report systematic experiments performed at different initial separation distances between particles and the use of our simple model allows the prediction of the settling behaviour and in particular the conditions for clusters formation. We thus show that particle aggregation can occur even for large initial distances between particles and within times that are small compared to the time scales in Newtonian fluids.

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PubMed1998

A Pulsed Field Gradient NMR Technique for the Determination of the Structure of Suspensions of Non-Brownian Particles with Application to Packings of Spheres.

The internal structure of systems of particles in a liquid is studied with a novel NMR technique based on the measurement of the squared modulus of the magnetization in presence of a pulsed field gradient. The formalism is analogous to the one used in classical scattering techniques (light, X-rays, neutrons); it allows similar information to be obtained about the structure (in particular, the structure factor S(q)). The main improvement is that the range of particles sizes is 10 µm to 1 mm, as compared with the range of the scattering techniques (<5 µm). The NMR technique was validated by studying packings of spherical particles of mean diameter 240 µm created by sedimentation. The profile of the experimental squared modulus of the magnetization versus the wave vector provides results for the mean size of particles and the compacity. The main feature is that it depends on the pair distribution function, and the present results are in good agreement with a model based on the Percus-Yevick approximation. This technique is then particularly adapted to systems such as non-Brownian suspensions, fluidized beds, porous media, and sediments. Copyright 1998 Academic Press.

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