Incompatible Liquids in Confined Conditions

In applications involving organic vapour, the performance of high surface area carbons is often challenged by water vapour in the atmosphere. Small angle neutron scattering (SANS), through its ability to distinguish between different components by means of contrast variation, is ideally suited to investigating the behaviour of adsorbed layers in simultaneous contact with a mixed vapour phase. Even at high relative humidity (RH), water alone forms a discontinuous film composed of clusters on the surface of the oxidized microporous carbon used for these studies. When toluene is also present, all the available carbon surface is wetted. Toluene and water adsorb as a single phase already at RH 11.5%, and the concentration of water present in the adsorbed phase is as high as 2.9 wt.%, far above its solubility in bulk toluene (0.033 wt.% at 25 deg C). At RH 87% the concentration of water in the adsorbed phase is four times higher, approximately 12 wt.%. The recently proposed mechanism of anchoring of the water by the aromatic molecules may provide an explanation for this phenomenon

La discrimination salariale selon le sexe chez les travailleurs immigrés: Étude du secteur de la fabrication au Canada

Rapport de recherche présenté à la Faculté des arts et des sciences en vue de l'obtention du grade de Maîtrise en sciences économiques

Structure of Latex-Silica Nanocomposite Films: A Small Angle Neutron Scattering Study

We report on the synthesis and structure of silica filled latex films. The main stage of the synthesis consists in physico-chemical manipulations of colloidal solutions of nanosilica and nanolatex beads, followed by drying and filmification. Hence, no mechanical energy which might contribute to building or destruction of aggregates of silica beads is supplied to the samples. We have analyzed the structure of the resulting filled latex films by means of Small Angle Neutron Scattering. The scattered intensity varies enormously with the physico-chemical parameters, indicating considerable structural modifications. To rationalize these results, we present a unified description of the data which successfully accounts for the main characteristics of the scattered intensity: the form factor of beads at large q vectors, the position of the intra- and inter-aggregate structure factor peaks, the small-q upturn observed in some cases, and the overall intensity in absolute units. This allows us to quantify the degree of aggregation of the silica in the matrix. It is found that the latter can be varied in a systematic manner by changing pH, silica volume fraction and quantity of added salt. In one extreme case, e.g., the aggregation number changes by a factor of about 1000 at constant silica volume fraction

Structural Characterization of Soft Interfaces by Standing-Wave Fluorescence with X-Rays and Neutrons

Abstract We present a review of standing-wave fluorescence techniques with x-rays and neutrons for the element-specific structural investigation of interfaces. The basic principles are introduced and typical measurement configurations with their advantages and limitations are compared. An overview of studies dealing with various types of interfaces is given. In particular, work on soft and biological matter in planar, interfacial geometries is discussed

Primary and Secondary Hydration Forces between Interdigitated Membranes Composed of Bolaform Microbial Glucolipids

To better understand lipid membranes in living organisms, the study of intermolecular forces using the osmotic pressure technique applied to model lipid membranes has constituted the ground knowledge in the field since four decades. However, the study of intermolecular forces in lipid systems other than phospholipids, like glycolipids, has gained a certain interest only recently. Even in this case, the work generally focus on the study of membrane glycolipids, but little is known on new forms of non-membrane functional compounds, like pH-responsive bolaform glycolipids. This works explores, through the osmotic stress method involving an adiabatic humidity chamber coupled to neutron diffraction, the short-range (< 2 nm) intermolecular forces of membranes entirely composed of interdigitated glucolipids. Experiments are performed at pH 6, when the glucolipid is partially negatively charged and for which we explore the effect of low (16 mM) and high (100 mM) ionic strength. We find that this system is characterized by primary and secondary hydration regimes, respectively insensitive and sensitive to ionic strength and with typical decay lengths of λ_H1= 0.37 ± 0.12 nm and λ_H2=1.97 ± 0.78 nm

Éditorial

En juillet 2019 était lancé le premier appel à contribution de la revue scientifique Patrimoines du Sud en vue de collecter l’état de la recherche et des expérimentations sur les champs croisés, et fertiles, des patrimoines et du numérique. Ce premier appel en inaugure d’autres à venir, tant cette rencontre entre patrimoine et technologie est porteuse d’avancées et de promesses à suivre. Pour cet opus n° 12, pas moins de 12 articles répondent à l’appel lancé et le dépassent. Celui-ci ciblait ..

SANS from Salt-Free Aqueous Solutions of Hydrophilic and Highly Charged Star-Branched Polyelectrolytes

International audienceScattering functions of sodium sulfonated polystyrene (NaPSS) star-branched polyelectrolytes with high sulfonation degrees were measured from their salt-free aqueous solutions, using the Small Angle Neutron Scattering (SANS) technique. Whatever the concentration c, they display two maxima. The first, of abscissa q 1 *, is related to a position order between star cores and scales as q 1 * 9 c 1/3. The second, of abscissa q 2 *, is also observed in the scattering function of a semi-dilute solution of NaPSS linear polyelectrolytes. In the dilute regime (c < c*, non-overlapping stars), peak abscissa does not depend on concentration c and is just an intramolecular characteristic associated with the electrostatic repulsion between arms of the same star. In the semi-dilute regime, due to the star interpenetration, the scattering function – through the peak position, reflects repulsion between arms of the same star or of different stars. The c threshold between these distinct c-dependencies of q 2 * in the dilute and semi-dilute regimes is estimated as c*. Just as simple is the measurement of the geometrical radius R of the star obtained from the q 1 * value at c* through the relation 2R = 2π/q 1 *. By considering NaPSS stars of the same functionality with different degrees of polymerization per arm N a , we find R scaling linearly with N a , suggesting an elongated average conformation of the arms. This is in agreement with theoretical predictions and simulations. Meanwhile the value of q 2 * measured in the dilute regime does not allow any inhomogeneous counterion distribution inside the stars to be revealed

Water modulates the lamellar structure and interlayer correlation of poly(perfluorooctyl acrylate) films: a specular and off-specular neutron scattering study

Comb-like polymers with pendant-like perfluorocarbon side chains self-assemble into smectic lamellae and have been extensively used as water-repellent, hydrophobic coating materials characterized by large water contact angles (θ > 120°). As poly(perfluorooctyl acrylate) films are “apparently hydrophobic” (θ > 120°), the interaction of such materials and water molecules has been largely overlooked. To unravel the molecular-level interactions between water and apparently hydrophobic polymers, specular and off-specular neutron scattering experiments were conducted at defined osmotic pressure ΠH2O. The poly{2-[(perfluorooctylethyl)carbamate]ethyl} acrylate (PFAUr-C₈), which had a carbamate linker, transitioned to another lamellar phase at 89 °C. At T = 25 °C; the lamellar periodicity of PFAUr-C₈ slightly increased with decreasing osmotic pressure, while the vertical correlation length increased. However, the poly[(perfluorooctyl)ethyl] acrylate (PFA-C₈) that did not contain a carbamate linker directly transitioned to a disordered phase at 84 °C. The lamellar periodicity of PFA-C₈ was largely independent of the osmotic pressure, suggesting that PFA-C₈ was poorly hydrated. Remarkably, the vertical correlation length decreased with decreasing osmotic pressure. Because hydration facilitated by the linker modulated the smectic lamellae of the poly(perfluoroalkyl acrylate), water molecules could be used to optimize the self-assembly of apparently hydrophobic liquid crystalline polymers

Interplay of Trans- and Cis-Interactions of Glycolipids in Membrane Adhesion

Glycolipids mediate stable membrane adhesion of potential biological relevance. In this article, we investigate the trans- and cis-interactions of glycolipids in molecular dynamics simulations and relate these interactions to the glycolipid-induced average separations of membranes obtained from neutron scattering experiments. We find that the cis-interactions between glycolipids in the same membrane leaflet tend to strengthen the trans-interactions between glycolipids in apposing leaflets. The trans-interactions of the glycolipids in our simulations require local membrane separations that are significantly smaller than the average membrane separations in the neutron scattering experiments, which indicates an important role of membrane shape fluctuations in glycolipid trans-binding. Simulations at the experimentally measured average membrane separations provide a molecular picture of the interplay between glycolipid attraction and steric repulsion of the fluctuating membranes probed in the experiments