Microfluidic Device for the Manipulation of Microparticles for Flow Cytometry Application

This work produces a unique microfluidic device that acts as a “lab on a chip,” conducting separation, mixing, and concentration of microparticles similar to that required by cell sorting flow cytometry applications. The passive two-dimensional device shows to be successful at separating polystyrene (PS) beads between 5 and 20 µm in diameter, mixing them with an external media, and concentrating them by 250% continuously with minimal sample preparation, while still being inexpensive, and effective. By implementing the microfluidic device, the processing steps are done within seconds due to its high throughput of 2 mL min⁻¹, wherein different hydrodynamic phenomena such as Dean's forces, inertial lift forces, and enhanced diffusion are taken advantage of.     

Shear induced clay organo‐modification: application to plasticized starch nano‐biocomposites

The present paper reports the successful development of a straightforward clay organo‐modification protocol named “Shear Induced Clay Organo‐modification” process, or SICO. To develop such a fast process, natural montmorillonite has been organo‐modified with cationic starch (surfactant) under shearing. According to the obtained results, this process allows the preparation of a pre‐exfoliated montmorillonite, organo‐modified by cationic starch (OMMT‐CS). Then, the OMMT‐CS has been dispersed into different plasticized starch‐based plastics, varying the polysaccharide botanical source, to obtain nano‐biocomposites displaying an exfoliated morphology. To establish the efficiency of this protocol and highlight this nano‐structuration, uniaxial tensile tests have been performed on these materials. The mechanical properties have been compared with those obtained with nano‐biocomposites elaborated with OMMT‐CS prepared with the conventional and efficient Exfoliation/Adsorption technique. Since comparable properties are obtained, we assume that the SICO process is a powerful technique to easily and quickly organo‐modify the montmorillonite clay and to obtain exfoliated nano‐biocomposites. Copyright © 2009 John Wiley & Sons, Ltd.     

In Situ Formation of Diazonium Salts from Nitro Precursors for Scanning Electrochemical Microscopy Patterning of Surfaces

Give me a tip : In situ production of diazonium salts from nitro compounds allows the use of diazonium chemistry for microelectrochemical patterning of surfaces by scanning electrochemical microscopy. The nitro precursor is reduced at the tip to the amine, which is diazotized in the interelectrode space as it diffuses (see picture). The tip acts as a source of diazonium salts, allowing sample derivatization just beneath the tip.

     

G-invariance faible et isovariance en planification expérimentale

In this Note, we state a polynomial characterization of weakly invariant designs and show how to derive the construction of weakly invariant designs for the action of a compact group of matrices on an experimental domain, whose interior is not empty, from the construction of rotatable designs. As a consequence, it enables us to search for weakly invariant designs using techniques coming from computational commutative algebra and to benefit from the cumulated knowledge of rotatable designs which have been intensively studied since the seminal paper of Box and Hunter. To cite this article: F. Bertrand, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Effective Debye length in closed nanoscopic systems: a competition between two length scales

The Poisson-Boltzmann equation (PBE) is widely employed in fields where the thermal motion of free ions is relevant, in particular in situations involving electrolytes in the vicinity of charged surfaces. The applications of this non-linear differential equation usually concern open systems (in osmotic equilibrium with an electrolyte reservoir, a semi-grand canonical ensemble), while solutions for closed systems (where the number of ions is fixed, a canonical ensemble) are either not appropriately distinguished from the former or are dismissed as a numerical calculation exercise. We consider herein the PBE for a confined, symmetric, univalent electrolyte and quantify how, in addition to the Debye length, its solution also depends on a second length scale, which embodies the contribution of ions by the surface (which may be significant in high surface-to-volume ratio micro- or nanofluidic capillaries). We thus establish that there are four distinct regimes for such systems, corresponding to the limits of the two parameters. We also show how the PBE in this case can be formulated in a familiar way by simply replacing the traditional Debye length by an effective Debye length, the value of which is obtained numerically from conservation conditions. But we also show that a simple expression for the value of the effective Debye length, obtained within a crude approximation, remains accurate even as the system size is reduced to nanoscopic dimensions, and well beyond the validity range typically associated with the solution of the PBE.