New Platform for Gravitational Microfluidic Using Ferrofluids

Among the large variety of microfluidic platforms, surface devices are a world apart. Electrowetting systems are used to control the displacement of droplets among predetermined pathways. More confidential, superhydrophobic surfaces are more and more described as new elements to guide spherical droplet reactors. As such, they can exhibit confinement properties analogous to channel-based microfluidics. In this article, we describe a new strategy to use superhydrophobic surfaces as a permanently tilted microfluidic platform, on which droplets containing iron oxide nanoparticles are guided with permanent magnets. These droplets are fed with water through a capillary tube until their weight exceeds the magnetic field force. Thus, the volume at which the droplet rolls off the surface is only governed by the initial quantity of magnetic nanoparticles and the tilting angle of the surface. This phenomenon provides a strategy for droplet dilution in a simple and reproducible manner, which is not that easy in microchannels, and a key advantage of open systems. As a proof of concept, we used this platform to prepare magnetic filaments by a salting-out process already described in large batches. By reducing salt concentration on the platform, we are able to control the electrostatic attractive interactions between iron oxide nanoparticles coated with poly(acrylic acid) and a positively charged polyelectrolyte [poly(diallyldimethylammonium chloride)]. The formation of nanostructured filaments was conducted in 2 min while more than 30 min was required for dialysis. Our results also illustrate the power of microfluidic reaction processes because such magnetic filaments could not be obtained through direct batch dilution because of mixing issues. Such microfluidic platforms could be useful for the efficient and simple dilution of systems where reactivity is controlled by concentration

Assessment of Transition Element Speciation in Glasses Using a Portable Transmission Ultraviolet–Visible–Near-Infrared (UV-Vis-NIR) Spectrometer

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High Resolution Spectroscopy on an X-ray Absorption Beamline

International audienceAbstract A bent crystal spectrometer based on the Rowland circle geometry has been tested on the BM30b/FAME beamline at the European Synchrotron Radiation Facility. The energy resolution of the spectrometer (1.3eV at the Cu K1 energy, i.e. 8047.78eV) allows to perform different kinds of measurements, including X-ray Absorption Spectroscopy, Resonant Inelastic X-ray Scattering and X-ray Raman Scattering experiments. The simplicity of the experimental device makes it easily implemented on a classical X-ray absorption beamline

Ion specific tuning of nanoparticle dispersion in an ionic liquid: A structural, thermoelectric and thermo-diffusive investigation

Dispersions of charged maghemite nanoparticles (NPs) in EAN (ethylammonium nitrate), a reference Ionic Liquid (IL), are here studied using a number of static and dynamical experimental techniques; Small Angle Scattering (SAS) of X-rays and of neutrons, dynamical light scattering and forced Rayleigh scattering. Particular insight is provided regarding the importance of tuning the ionic species present at the NP/IL interface; In this work we compare the effect of Li+, Na+ or Rb+ ions. The nature of these species has here a clear influence on the short-range spatial organization of the ions at the interface and thus on the colloidal stability of the dispersions, governing both the NP/NP and NP/IL interactions, which are here both evaluated. The overall NP/NP interaction is either attractive or repulsive. It is characterized by determining, thanks to the SAS techniques, the second virial coefficient A2, which is found independent of temperature. The NP/IL interaction is featured by the dynamical effective charge ξoeff of the NPs and by their entropy of transfer SˆNP (or equivalently their heat of transport QˆNP) determined here thanks to thermoelectric and thermodiffusive measurements. For repulsive systems, an activated process rules here the temperature dependence of these two latter quantities

Ion specific tuning of nanoparticle dispersion in an ionic liquid: A structural, thermoelectric and thermo-diffusive investigation

International audienceDispersions of charged maghemite nanoparticles (NPs) in EAN (ethylammonium nitrate) a reference Ionic Liquid (IL), are here studied using a number of static and dynamical experimental techniques; Small Angle Scattering..

High energy resolution five-crystal spectrometer for high quality fluorescence and absorption measurements on an X-ray Absorption Spectroscopy beamline

International audienceFluorescence detection is classically achieved with a solid state detector (SSD) on x-ray absorption spectroscopy (XAS) beamlines. This kind of detection however presents some limitations related to the limited energy resolution and saturation. Crystal analyzer spectrometers (CAS) based on a Johann-type geometry have been developed to overcome these limitations. We have tested and installed such a system on the BM30B/CRG-FAME XAS beamline at the ESRF dedicated to the structural investigation of very dilute systems in environmental, material and biological sciences. The spectrometer has been designed to be a mobile device for easy integration in multi-purpose hard x-ray synchrotron beamlines or even with a laboratory x-ray source. The CAS allows to collect x-ray photons from a large solid angle with five spherically bent crystals. It will cover a large energy range allowing to probe fluorescence lines characteristic of all the elements from Ca (Z = 20) to U (Z = 92). It provides an energy resolution of 1-2 eV. XAS spectroscopy is the main application of this device even if other spectroscopic techniques (RIXS, XES, XRS, etc.) can be also achieved with it. The performances of the CAS are illustrated by two experiments that are difficult or impossible to perform with SSD and the complementarity of the CAS vs SSD detectors is discussed