Dilational viscoelasticity and relaxation properties of interfacial electrostatic complexes between oppositely charged hydrophobic and hydrophilic polyelectrolytes

Strongly adsorbing hydrophobic cationic polyelectrolyte, Eudragit RS, containing approximately 2.5 mol% of pendent hydrophilic trimethylammonium (TMA) groups irreversibly adsorbs from its methylene chloride (MCl) solution at the MCl/water interface and forms solid-like adsorption layers (ALs). Submitted to periodic dilational deformations with the standard radial frequency omega(0)=0.63 rad/s, these ALs exhibit relatively high dilational storage modulus E\u27 approximately 20 mN/m and practically zero loss modulus E\u27\u27 at the bulk concentration C(Eud)=4 x 10(-3)g/L. The frequency scanning of these ALs in the diapason omega=0.01-0.63rad/s and the approximation of the experimental dependences E\u27(omega) and E\u27\u27(omega) by two relaxation times rheological model makes it possible to estimate the crossing frequency of these ALs determined from the condition E\u27(omega(c))=E\u27\u27(omega(c)) as omega(c) approximately 5 x 10(-4)rad/s. Upon dissolving the hydrophilic anionic polyelectrolyte, chitosan sulfate (ChS), in the water phase (C(ChS)=3 x 10(-2)g/L) the electrostatic interpolyelectrolyte complexes form at the MCl/water interface. The elasticity moduli E\u27 and E\u27\u27 of these mixed AL did not undergo remarkable variations, but the crossing frequency is sharply increased by approximately 10 times becoming equal to omega(c) congruent with 3 x 10(-3)rad/s. The increase of omega(c) certifies for the liquefaction of mixed Eudragit RS/ChS adsorption layers. A remarkable decrease of the storage modulus down to E\u27=8 mN/m and simultaneous increase of the crossing frequency up to omega(c) congruent with 10(-2)rad/s occurs upon increasing the concentrations of both components, Eudragit RS and ChS, up to 0.1g/L. The liquefaction effect in the mixed ALs of oppositely charged polyelectrolytes was explained on the basis of the proposed relaxation mechanism. The effect of the liquefaction of adsorption layers of strongly adsorbing hydrophobic polyelectrolytes by formation of interpolyelectrolyte complexes with hydrophilic polyelectrolytes must be taken into account in the production of nano-capsules and nano-fibers

Streamlining Ground Station Network Compatibility Test for Small Satellites

A team of eight subject matter experts at NASA Goddard Space Flight Center (GSFC) completed a Lean Six Sigma project to identify process improvements for the compatibility test process for small satellites planning to use the NASA Near Earth Network (NEN). Ground station network compatibility testing is designed to reduce the risk to missions by resolving issues between the spacecraft's flight communication and navigation components and the ground systems prior to launch. Compatibility testing, which consists of a series of tests performed over a period of months and documented in reports, is an important step meant to prevent post-launch anomalies that could lead to expensive troubleshooting or mission failure. Compared to traditional missions, small satellite missions typically have a smaller budget and compressed schedules, which can result in small satellite projects' willingness to accept the risk associated with less comprehensive compatibility testing. Optimization and or refinement of the compatibility test process for small satellite missions could alleviate some of the pressures inherent with these factors. The goal of the Lean Six Sigma project was to develop alternative scalable methods of compatibility testing for small satellites. The Lean Six Sigma approach and the results of the project are reviewed in this paper

Measurement of cross sections for 22Na, 20-22Ne and 36-42Ar in the spallation of Mg, Al, Si, Ca and Fe. Production ratios of some cosmogenic nuclides in meteorites

We measured the cross sections of 22Na, 20,21,22Ne and 36,38,39,42Ar in nuclear reactions induced by the proton bombardment of Mg, Al, Si, Ca and Fe at several energies between 0.059 and 24 GeV using highsensitivy mass-spectrometry for noble gases and γ-counting for 22Na. We then evaluated the cross section ratio versus energy for the 22Na/22Ne, 26Al/21Ne, 39Ar/38Ar and 36Cl/ 36Ar radioactive-stable pairs of isotopes, which are useful for measuring the exposure age of meteorites. From the results alone, we can set some limits to the corresponding production ratios in iron meteorites, but not in stony objects because a knowledge of chemical abundances of Na, Mg, Al, Si, S, K, Ca, Fe, and shielding conditions are required.Nous avons mesuré, par spectrométrie de masse des gaz rares et par comptage γ, les sections efficaces σ des réactions nucléaires conduisant à 22Na, 20-22Ne et 36-42Ar dans des cibles de Mg, Al, Si, Ca et Fe bombardées par des protons de 0,059 à 24 GeV. Ces nouvelles mesures et celles existant dans la littérature nous ont permis d'évaluer les rapports des sections efficaces σR/σs en fonction de l'énergie de quatre paires d'isotopes, l'un stable S et l'autre radioactif R : 22Na/22Ne, 26Al/ 21Ne, 39Ar/38Ar et 36Cl/36Ar. Ces paires d'isotopes permettent de calculer l'âge d'exposition des météorites, si on connait le rapport de leur taux de production PR/ PS. Notre travail établit des limites aux rapports P R/Ps dans les météorites de fer à partir de la seule considération des rapports σR/σS. Dans les météorites de pierre on peut seulement montrer, par cette approche, l'importance des effets de composition chimique et de blindage

Cinétique de réactions partiellement limitées par la diffusion XIX Un algorithme simple pour la détermination des paramètres des constantes de vitesse apparente

Partant des hypothèses de Smoluchowski, un algorithme simple est proposé pour calculer la constante apparente aux temps longs, incluant divers effets physico-chimiques pouvant intervenir au cours d'une réaction dont la cinétique est limitée par la diffusion. Quelques exemples d'application sont présentés

Microstructured Reactors Designed by Stereolithography and Characterized by Fluorescent Probes

The main objective of this research was to define a structured and functionalized support for future biomedical applications (model of “low-density bioarray”). The experiments were carried out by using stereolithography process with a special SU-8 photoresist and the reproducibility of the method was studied by analyzing the surface profile of the support. Finally, a matrix of regular controlled sized wells was fabricated. Chemical reactions leading to covalent grafting were run to demonstrate that the inner surface of the wells remains still reactive after polymerization. The grafting of fluorophores with carboxylic functions activated by N-hydroxysuccinimide was studied as function of time, in order to determine the best reactions, conditions. Then, the grafting of two distinct fluorescent probes was led simultaneously inside the wells, showing the possibility of spatial localization of diverse reactions on the same support. The covalent and localized bindings were confirmed by fluorescence spectroscopy and microscopy analyses