Capture of colloidal particles by a moving microfluidic bubble

We study particle capture at a microfluidic air–liquid interface and highlight the effects of confinement on colloidal adsorption

Intermittent dynamics of bubble dissolution due to interfacial growth of fat crystals

International audienceFoams are inherently unstable objects, that age and disappear over time. The main cause of foam aging is Ostwald ripening: smaller air bubbles within the foam empty their gas content into larger ones. One strategy to counter Ostwald ripening consists in creating armored bubbles, where solid particles adsorbed at the air/liquid interface prevent bubbles from shrinking below a given size. Here, we study the efficiency of coating air bubbles with fat crystals to prevent bubble dissolution. A monoglyceride, monostearin, is directly crystallized at the air/oil interface. Experiments on single bubbles in a microfluidic device show that the presence of monostearin fat crystals slows down dissolution, with an efficiency that depends on the crystal size. Bubble ripening in the presence of crystals exhibits intermittent dissolution dynamics, with phases of arrest, when crystals jam at the interface, followed by phases of dissolution, when monostearin crystals are ejected from the interface. In the end, crystals do not confer enough mechanical strength to the bubbles to prevent them from fully dissolving

Fatty acid monolayers on randomly nanostructured inorganic surfaces: Interplay of wettability, chemistry and topography

Understanding the wetting properties of chemically-modified inorganic surfaces with random nanoscale topography is of fundamental importance for diverse applications. This issue has hitherto continuously been the subject of considerable controversies. Herein, we report a thorough investigation of the wettability-topography-chemistry balance for a surface with random nanoscale topography, the main challenge being decoupling topography from surface chemistry. For this purpose, we use a superficially nanostructured aluminum substrate chemically modified by fatty acid monolayers. From AFM data, we extract a variety of parameters describing the surface topography by means of variogram calculations, a method originally developed by geo-statists to explore large surfaces. Moreover, by using a power transform approach, we establish a consistent relationship relating wettability, topography and surface chemistry. Interestingly, we demonstrate that the water contact angle comprises a contribution due to the surface composition, originating from hydrophilization through alkyl chains, and a contribution due to the surface topography. This model is valid in the Wenzel region, and may suggest ways to tune the wetting properties of inorganic surfaces with nanoscale stochastic topographies

Self-Assembly of Fatty Acids on Hydroxylated Al Surface and Effects of Their Stability on Wettability and Nanoscale Organization

International audienc

Intermittent dynamics of bubble dissolution due to interfacial growth of fat crystals

International audienceFoams are inherently unstable objects, that age and disappear over time. The main cause of foam aging is Ostwald ripening: smaller air bubbles within the foam empty their gas content into larger ones. One strategy to counter Ostwald ripening consists in creating armored bubbles, where solid particles adsorbed at the air/liquid interface prevent bubbles from shrinking below a given size. Here, we study the efficiency of coating air bubbles with fat crystals to prevent bubble dissolution. A monoglyceride, monostearin, is directly crystallized at the air/oil interface. Experiments on single bubbles in a microfluidic device show that the presence of monostearin fat crystals slows down dissolution, with an efficiency that depends on the crystal size. Bubble ripening in the presence of crystals exhibits intermittent dissolution dynamics, with phases of arrest, when crystals jam at the interface, followed by phases of dissolution, when monostearin crystals are ejected from the interface. In the end, crystals do not confer enough mechanical strength to the bubbles to prevent them from fully dissolving

Morphology-controlled precipitation of cerium oxalate crystals: The effect of water in nanostructured solvents

International audienceThe ability to control the morphology of precipitated cerium oxalate material results in determinate evidence to its final properties. In this study, we demonstrate that surfactant-free nanostructured low-water solvents have a huge potential for controlling the morphology of a cerium oxalate powder. To this aim, an in-depth investigation of the reaction between cerium nitrate and oxalic acid is carried out, by varying both the relative concentration of the two reagents (around the stoichiometric value) and the composition of the water/propanediol/octanol ternary solvent (especially in the low-water content nanostructured domain). Thanks to the complementary of observation methods: microscopy (confocal microscopy with fluorophores and environmental SEM) and X-ray scattering (SAXS and WAXS), we evidenced the role of the solvent in the growth kinetics and directional aggregation of the precipitates—the two major factors determining the final morphology of the particles. Besides the possible confinement effect in nanodroplets, compact “dense-branching” particles, achieved in low-water content solvents, unveil the strong role of the surface forces in the aggregation mechanisms. This is consistent with the prevailing capillary forces at water/oil/solid triple points in ternary solvents. These new results confirm the high potential of nanostructured solvents for controlling the size and shape of hydrated precipitated particles

Organic adlayer on inorganic materials : XPS analysis selectivity to cope with adventitious contamination

This work addresses the ubiquitous presence of organic contaminants at inorganic solid surfaces and the improvement of XPS analysis selectivity to cope with it. Water contact angle measurements showed that the adsorption of organic contaminants occurs readily in ambient air, and faster and more extensively under high vacuum. It is stronger on stainless steel (SS) compared to silica and is significantly reduced when SS is sterilized by autoclaving. The reliability of XPS data was evaluated (selectivity, precision, accuracy) by correlations between spectral data incorporating a large amount of results obtained with different XPS spectrometers on SS and glass samples cleaned in different ways and conditioned with several biomacromolecules. The methodology used allows a discrimination to be made between contaminants and deliberately adsorbed biomacromolecules, and offers perspectives for tracking the source of contamination. Furthermore, a discrimination can be made between oxygen from the organic adlayer and oxygen from the substrate, and the O 1s component above 532.0 eV observed for SS is shown to be due to organic contaminants rather than adsorbed water. This approach offers new perspectives to examine the interactions (displacement or not) between contaminants and compounds of interest, e.g. proteins, at the stage of the adsorption process

Lipid Layers on Nanoscale Surface Topography: Stability and Effect on Protein Adsorption

International audienc

Unravelling surface changes on Cu-Ni alloy upon immersion in aqueous media simulating catalytic activity of aerobic biofilms

Cu-Ni alloys are extensively used in contact with natural waters and are impacted by microbial activities of biofilms. The mechanisms by which surface changes occur upon immersion remain not well understood. Herein, an aerobic microbial activity of natural biofilms is mimicked by the enzymatic generation of an oxidizing agent and an organic acid. Surface changes are probed through a detailed analysis of XPS spectra which allowed a distinction between compounds of organic and inorganic nature to be made. Results show that the surface is composed of copper oxides/hydroxides, presumably Cu2O and Cu(OH)2 and Ni hydroxides. The enzyme-catalyzed reaction causes a significant depletion of Ni and inorganic oxygen, while the concentration of copper, CuI and CuII, varies only slightly. Surface changes concern the organic phase; the amount of organic compounds strikingly increases in the presence of enzymes, and the XPS spectra reveal the accumulation of compounds with high oxidized carbon content, attributed to adsorbed gluconate. Correlations between spectral data suggest the formation of Cu-gluconate complex, probably through coordinative bonds between gluconates and CuII on the oxide layer. These findings are particularly important to properly evaluate the impact of microbial activities on the sustainability of Cu-Ni alloys upon natural exposures

Arresting dissolution by interfacial rheology design

ISSN:0027-8424ISSN:1091-649