Numerical investigation of generalized Graetz problem in circular tube with a mass transfer coupling between the solid and the liquid

International audienceThe unsteady diffusion equation in a tube and the advection/diffusion equation in laminar flow in a liquid of a solute are theoretically established. The most important parameters are the migration strength α and the so-called Graetz number Gr. The former dimen-sionless number is the product of the partition coefficient of the solute at the solid/liquid interface, the ratio of the tube thickness to the interior radius and the ratio of diffusion coefficients of the solute in the liquid and in the solid. The Graetz number Gr is the ratio of the diffusion time scale in the liquid based on the interior radius of the pipe to the advection time over the tube length. The problem is applied to the plasticizer migration from a polyvinyl chloride material to a liquid with the safety food applications in mind. The migration of the plasticizer is solved numerically for various tube sizes, flow conditions and partition coefficients of the plasticizer in the liquid. For comparison, the numerical results obtained in static condition are also provided. The average plasticizer concentration in the liquid behaves following two main regimes as a function of the migration strength. When α is much smaller than one, the average plasticizer concentration in the liquid is an algebraic function of the axial coordinate, z, at the power two third and increases linearly with time. Conversely, when α is much larger than one, the average plasticizer concentration is linear as a function of axial distance and increases as a function of the square root of time. Moreover, the concentration is much smaller of few orders of magnitude in dynamic condition than in static working showing that in the context of food contamination the dynamic approach is more appropriate and relevant for demonstration of compliance with the safety authorities requirements

Triple line destabilization: Tuning film thickness through meniscus curvature

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All-silica nanofluidic devices for DNA-analysis fabricated by imprint of sol-gel silica with silicon stamp.

International audienceWe present a simple and cheap method for fabrication of silica nanofluidic devices for single-molecule studies. By imprinting sol-gel materials with a multi-level stamp comprising micro- and nanofeatures, channels of different depth are produced in a single process step. Calcination of the imprinted hybrid sol-gel material produces purely inorganic silica, which has very low autofluorescence and can be fusion bonded to a glass lid. Compared to top-down processing of fused silica or silicon substrates, imprint of sol-gel silica enables fabrication of high-quality nanofluidic devices without expensive high-vacuum lithography and etching techniques. The applicability of the fabricated device for single-molecule studies is demonstrated by measuring the extension of DNA molecules of different lengths confined in the nanochannels

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Self-assembled Titanium Calcium Oxide Nanopatterns as versatile Reactive Nanomasks for Dry Etching Lithographic Transfer with High Selectivity

International audienceWe report the simple preparation of ultra-thin self-assembled nanoperforated titanium calcium oxide films and their use as Reactive NanoMasks for selective dry etching of silicon. The novel reactive nanomask is composed of TiO2 to which up to 50% of Ti was replaced by Ca (CaxTi(1-x)O(2-x)). The system has been prepared by evaporation induced self-assembly of dip-coated solution of CaCl2, TiCl4 and poly(butadiene-block-ethylene oxide) followed by 5 min of thermal treatment at 500 °C in air. The mask exhibits enhanced selectivity by forming a CaF2 protective layer in the presence of a chemically reactive fluorinated plasma. In particular it is demonstrated that ordered nano-arrays of dense Si pillars, or deep cylindrical wells, with high aspect ratio i.e. lateral dimensions as small as 20 nm and height up to 200 nm, can be formed. Both wells and pillars were formed by tuning the morphology and the homogeneity of the deposited mask. The mask preparation is extremely fast and simple, low-cost and easily scalable. Its combination with reactive ion etching constitutes one of the first examples of what can be achieved when sol-gel chemistry is coupled with top-down technologies. The resulting Si nanopatterns and nanostructures are of high interest for applications in many fields of nanotechnology including electronics and optics. This work extends and diversifies the toolbox of nanofabrication methods

High Efficiency White Luminescence of Alumina doped ZnO

International audienceThe application of Alumina-doped ZnO (AZO) films as luminescent material for large area lighting sources has been evaluated. Thin films were grown on quartz using magnetron sputtering and subsequently annealed under argon atmosphere in a rapid thermal annealing experiment. Below 550 °C, red-shift of the optical band gap and increase of the visible emission are observed in agreement with Al diffusion and formation of interstitial oxygen atoms. At temperatures higher than 800 °C, diffusion is activated and Ostwald ripening leads to the formation of larger grains and an increase of the crystalline phase. The photoluminescence (PL) intensity is enhanced, specifically in the UV range. As a result the emission spectrum of AZO thin films can be adjusted by the annealing conditions, with equal contributions from the UV and orange parts of the PL spectrum resulting in an efficient white emission as quantified using the color space map of the Commission Internationale de l'Éclairage