Transfer (soaking, drying) in multifunctional doubly porous materials

La plupart des matériaux de construction à structure multi-échelle, comme le bois, le béton de chanvre ou le torchis, présentent des propriétés de contrôle de l’humidité remarquables. Pour mieux en comprendre l’origine, nous étudions les propriétés de transfert de systèmes biporeux modèles basés sur des matériaux polymères conçus par l’approche à double agent porogène avec, dans la matrice de petits pores (SP), différentes morphologies de pores larges (LP) : cubiques ou sphériques, dispersés, ou connectés par des constrictions abruptes ou plus lisses, et avec un contrôle de la mouillabilité. Deux catégories de structures biporeuses sont identifiées, présentant des propriétés très différentes. Tout d’abord, lorsque les pores larges sont dispersés au sein de la matrice SP, le liquide envahit la matrice microporeuse et contourne les inclusions, emprisonnant des poches d’air. Quel que soit la fraction volumique des LP, l’imbibition est très bien décrite avec différents fluides par la théorie usuelle de Washburn dans la matrice SP. D’autre part, quand les pores larges constituent un réseau continu, la dynamique d’imbibition est déterminée par la compétition et les interactions entre les deux réseaux poreux (matrice microporeuse et réseau connecté de macropores). Si l’ascension capillaire au sein du réseau macroporeux est rapide (connexions douces entre LP), elle gouverne la dynamique d’imbibition dans le matériau biporeux, et le liquide peut ensuite être drainé vers la matrice microporeuse proche. En revanche, si l’imbibition est lente dans le réseau macroporeux (constrictions abruptes entre LP), alors la matrice de micropores contrôle la dynamique d’imbibition, pouvant même l’accélérer par un effet de synergie entre les réseaux poreux, visible avec l’apparition de deux fronts capillaires.Le séchage des matériaux biporeux saturés est étudié par relaxation RMN 1H et suivi visuel de contraction. Nous montrons alors que les mécanismes de séchage dépendent de la connectivité du réseau de pores larges au sein de la matrice microporeuse. Les pores larges dispersés se désaturent en premier et de façon homogène, du fait d’une compression du système résultat de la pression capillaire, tandis qu’un réseau de pores larges connectés est drainé en premier aussi, mais pore par pore sans contraction du système. La vitesse de séchage reste constante pendant la majeure partie de la désaturation dans les deux casSome multi-scale building materials, like wood, hemp concrete or daub, exhibit high potential properties in terms of hygrometric diffusion (moisture expelling out of a house). In order to get a better insight into those properties, we investigate fluid transportation (soaking/drying) in doubly porous model systems based on polymeric materials envisioned by the double porogen templating approach. They are elaborated with controlled hydrophilicity and various large pore (LP) morphologies within the small pores matrix (SP): cubic or spherical, dispersed or connected by sharp-edged or smoother constrictions. We identify two categories of biporous structures leading to very diverging properties. Firstly, when dispersed large pores are included within the SP matrix, the liquid penetrates in the microporous matrix and the large pores absorb little to no water, and confining air inside them. Regardless the volume ratio of dispersed LP, the rising front is well described with different fluids by the classical Washburn theory inside the matrix only. On the other hand, when the large pores constitute a connected network, a competition between the imbibition within both porous networks (microporous matrix and macroporous network interacting with each other) determine the imbibition mechanism. If the rising of capillary front is fast in the macroporous network (smooth connexions between LP), it dominates the imbibition process, and the liquid can be drained by the smaller pore size close to it. In contrast, if the imbibition is slow in the macroporous network (sharp-edged constrictions between LP), then the microporous matrix controls the dynamic of soaking, and can speed it up with synergetic action highlighted by two distinctive rising fronts. The drying of those saturated biporous materials is investigated with 1H NMR relaxation and contraction monitoring. We demonstrate that drying mechanisms depends on the connectivity of large pores inside the microporous matrix too. Dispersed LP are homogeneously emptying first, resulting from a compression induced by the capillary pressure, whereas a connected LP network is emptying first too, but heterogeneously pore after pore. The drying rate is still constant in both cases during the majority of the desaturatio

Transferts (imbibition, séchage) dans des matériaux bi-poreux multifonctionnels

Some multi-scale building materials, like wood, hemp concrete or daub, exhibit high potential properties in terms of hygrometric diffusion (moisture expelling out of a house). In order to get a better insight into those properties, we investigate fluid transportation (soaking/drying) in doubly porous model systems based on polymeric materials envisioned by the double porogen templating approach. They are elaborated with controlled hydrophilicity and various large pore (LP) morphologies within the small pores matrix (SP): cubic or spherical, dispersed or connected by sharp-edged or smoother constrictions. We identify two categories of biporous structures leading to very diverging properties. Firstly, when dispersed large pores are included within the SP matrix, the liquid penetrates in the microporous matrix and the large pores absorb little to no water, and confining air inside them. Regardless the volume ratio of dispersed LP, the rising front is well described with different fluids by the classical Washburn theory inside the matrix only. On the other hand, when the large pores constitute a connected network, a competition between the imbibition within both porous networks (microporous matrix and macroporous network interacting with each other) determine the imbibition mechanism. If the rising of capillary front is fast in the macroporous network (smooth connexions between LP), it dominates the imbibition process, and the liquid can be drained by the smaller pore size close to it. In contrast, if the imbibition is slow in the macroporous network (sharp-edged constrictions between LP), then the microporous matrix controls the dynamic of soaking, and can speed it up with synergetic action highlighted by two distinctive rising fronts. The drying of those saturated biporous materials is investigated with 1H NMR relaxation and contraction monitoring. We demonstrate that drying mechanisms depends on the connectivity of large pores inside the microporous matrix too. Dispersed LP are homogeneously emptying first, resulting from a compression induced by the capillary pressure, whereas a connected LP network is emptying first too, but heterogeneously pore after pore. The drying rate is still constant in both cases during the majority of the desaturationLa plupart des matériaux de construction à structure multi-échelle, comme le bois, le béton de chanvre ou le torchis, présentent des propriétés de contrôle de l’humidité remarquables. Pour mieux en comprendre l’origine, nous étudions les propriétés de transfert de systèmes biporeux modèles basés sur des matériaux polymères conçus par l’approche à double agent porogène avec, dans la matrice de petits pores (SP), différentes morphologies de pores larges (LP) : cubiques ou sphériques, dispersés, ou connectés par des constrictions abruptes ou plus lisses, et avec un contrôle de la mouillabilité. Deux catégories de structures biporeuses sont identifiées, présentant des propriétés très différentes. Tout d’abord, lorsque les pores larges sont dispersés au sein de la matrice SP, le liquide envahit la matrice microporeuse et contourne les inclusions, emprisonnant des poches d’air. Quel que soit la fraction volumique des LP, l’imbibition est très bien décrite avec différents fluides par la théorie usuelle de Washburn dans la matrice SP. D’autre part, quand les pores larges constituent un réseau continu, la dynamique d’imbibition est déterminée par la compétition et les interactions entre les deux réseaux poreux (matrice microporeuse et réseau connecté de macropores). Si l’ascension capillaire au sein du réseau macroporeux est rapide (connexions douces entre LP), elle gouverne la dynamique d’imbibition dans le matériau biporeux, et le liquide peut ensuite être drainé vers la matrice microporeuse proche. En revanche, si l’imbibition est lente dans le réseau macroporeux (constrictions abruptes entre LP), alors la matrice de micropores contrôle la dynamique d’imbibition, pouvant même l’accélérer par un effet de synergie entre les réseaux poreux, visible avec l’apparition de deux fronts capillaires.Le séchage des matériaux biporeux saturés est étudié par relaxation RMN 1H et suivi visuel de contraction. Nous montrons alors que les mécanismes de séchage dépendent de la connectivité du réseau de pores larges au sein de la matrice microporeuse. Les pores larges dispersés se désaturent en premier et de façon homogène, du fait d’une compression du système résultat de la pression capillaire, tandis qu’un réseau de pores larges connectés est drainé en premier aussi, mais pore par pore sans contraction du système. La vitesse de séchage reste constante pendant la majeure partie de la désaturation dans les deux ca

Pectins from citrus peel cell walls contain homogalacturonans homogenous with respect to molar mass, rhamnogalacturonan I and rhamnogalacturonan II

International audiencePectins of different structures were extracted from citrus peels with water, oxalate, hot dilute hydrochloric acid and cold dilute sodium hydroxide. Homogalacturonans (HGs) were isolated from the four pectins by mild acid hydrolysis after deesterification. The study of their macromolecular properties revealed that they have similar number- and weight-average degrees of polymerisation, in the range of 81–117 galacturonic acid units, irrespective of the initial pectin. It was inferred that citrus peel pectins consist of HG strectches of similar lengths whatever the mode of extraction. Rhamnogalacturonan I (RG I) and rhamnogalacturonan II (RG II) were isolated from the oxalate- and the acid-extracted pectins using an endo-1,4-α-polygalacturonase followed by anion-exchange and size-exclusion chromatographies. RG I was composed mainly of arabinose, galactose, galacturonic acid and rhamnose, suggesting the presence of arabinan and/or (arabino)galactan side chains. Debranched RG I (dRG I) was obtained by treating the RG I arising from acid-extracted pectin with endo-1,5-α-l-arabinanase, endo-1,4-β-d-galactanase, α-l-arabinofuranosidase and β-d-galactosidase in admixture. The molar ratios of galacturonic acid to rhamnose of RGs I and dRG I were very close to 1/1, indicating a strict repeating [GalA–Rha]n pattern in the backbone. It is concluded that citrus pectins consist predominantly of HG, with a few RG I and a minor RG II fraction

Synergistic actions of mixed small and large pores for capillary absorption through biporous polymeric materials

International audienceWater absorption in porous media is an important process involved in numerous materials for various applications, such as in the building industry, food processing and bioengineering. Designing new materials with appropriate absorption properties requires an understanding of how absorption behavior depends on both the material's morphology and the properties of the solid matrix, i.e. hydrophilic/ hydrophobic nature and swelling/deformation properties. Although the basic principles of imbibition are well-known for simple porous systems, much less is known about absorption in complex porous systems, in particular those containing several coexisting porous phases, such as wood for example. Here, water absorption is studied for model porous organic materials exhibiting several degrees of hydrophobicity and two pore size levels, either as monoporous materials (large or small pores) or as biporous materials (mixed large and small pores). The interconnected biporous structure is designed via a double porogen templating approach using cubic sodium chloride particles as templates for the generation of the larger pore size (250-400 mm) and i-PrOH as a porogenic solvent for the smaller pore size (2-5 mm). While absorption for the small pore material is well described by the classical Washburn theory, the large pore material shows a drastic reduction in the imbibition rate. This behavior is attributed to the slow breakthrough mechanism for the water interface at sharp edge connections between pores. Remarkably, this slow regime is suppressed for the biporous material and the imbibition rate is even higher than the sum of rates obtained for its monoporous counterparts, which highlights the synergistic action of mixed small and large pores

Drying of a Compressible Biporous Material

International audienceWe study the consequences of drying on the internal structure of compressible materials containing pores of different sizes, which may be seen as model systems of sponges or wood. With the help of original techniques, we devise biporous media with different relative amounts of small and large pores, and follow the evolution of the liquid fraction simultaneously in each pore type. We show that in a compressible biporous medium with dispersed large pores (i.e., not directly connected) drying induces the homogeneous emptying of the large pores first, due to their compression, along with some compression of the small-pore matrix. In contrast, when the large pores are connected, they successively empty without compression. In both cases, the small pores start or finish to empty in the next stage, and a constant drying rate is observed during most of the time, thanks to liquid films maintaining the contact of the liquid network with the free surface of the sample

Probe, Sample, and Instrument (PSI): The Hat-Trick for Fluorescence Live Cell Imaging

International audienceCell Imaging Platforms (CIPs) are research infrastructures offering support to a number of scientific projects including the choice of adapted fluorescent probes for live cell imaging. What to detect in what type of sample and for how long is a major issue with fluorescent probes and, for this, the “hat-trick” “Probe–Sample–Instrument” (PSI) has to be considered. We propose here to deal with key points usually discussed in CIPs including the properties of fluorescent organic probes, the modality of cell labeling, and the best equipment to obtain appropriate spectral, spatial, and temporal resolution. New strategies in organic synthesis and click chemistry for accessing probes with enhanced photophysical characteristics and targeting abilities will also be addressed. Finally, methods for image processing will be described to optimize exploitation of fluorescence signals

Synthesis and optical properties of dyes encapsulated in gold hollow nanoshells

International audienc

The Caravel heX-Mesh pavilion, illustration of a new strategy for gridshell rationalization

International audienceThe fabrication of a freeform structural envelope is usually a highly complex task. The costliest aspect is often the connections between the constitutive parts. The Caravel heX-Mesh Pavilion is a prototype that demonstrates a new rationalization strategy. Its structure, composed of a hexagonal grid of beams and cladding panels, is based on a geometry that rationalizes connections at two levels: firstly, nodes are free of geometrical torsion and are repetitive: only two types of nodes are used. Secondly, panels can easily be connected to the support beams as they are orthogonal to each other. The mechanical behavior is validated by finite-element analysis. We generate these meshes by numerical optimization from a smooth target surface, with an initialization derived from the asymptotic case and surface theory. The pavilion shows an alternative way of rationalizing a gridshell beyond the popular planar-quad meshes and circular/conical meshes. It also demonstrates a way to generate hexagonal gridshells which are not necessarily synclastic, this limitation being typically imposed to achieve planarity of cladding panels

Hybridating vertex and face normals to design torsion-free gridshells: application to the X-Mesh pavilion

International audienceThe fabrication of a freeform structural envelope is usually a highly complex task. The costliest aspect is often the connections between the constitutive parts. X-Mesh is a pavilion that demonstrates a new rationalization strategy. Its structure, composed of a hexagonal grid of beams and cladding panels, is based on a geometry that rationalizes connections at two levels: firstly, nodes are repetitive, only two types of nodes are used. Secondly, panels can easily be connected to the support beams as they are orthogonal to each other. We prove that the proposed geometrical configuration can be asymptotically built on a smooth surface. We generate the meshes by numerical optimization from a smooth target surface, with an initialization derived from the asymptotic case. This pavilion shows another way of rationalizing a gridshell beyond the popular planar-quad meshes and circular/conical meshes. It also demonstrates a way to generate hexagonal gridshells which are not necessarily synclastic, this limitation being typically imposed to achieve planarity of cladding panels

Transparent Plasmonic Nanocontainers Protect Organic Fluorophores against Photobleaching

International audienceNumerous research efforts are investigating the possibility of using light interactions with metallic nanoparticles to improve the fluorescence properties of nearby molecules. Few investigations have considered the encapsulation of molecules in metallic nanocavities. In this paper, we present the optical properties of new hybrid nanoparticles consisting of gold nanoshells and fluorescent organic dyes in their liquid cores. Microspectroscopy on single nanoparticle demonstrates that the extinction spectra are in good agreement with Mie's theory. Finite difference time domain (FDTD) calculations reveal that excitation and emission radiations are efficiently transmitted through the thin gold nanoshells. Thus, they can be considered as transparent plasmonic nanocontainers for photoactive cores. In agreement with FDTD calculations, measurements show that fluorophores encapsulated in gold nanoshells keep their brightness, but they show fluorescence lifetimes 1 order of magnitude shorter. As a salient consequence, the photoresistance of encapsulated organic dyes is also improved by an order of magnitude. This unusual ultraviolet photoresistance results from the reduced probability of triplet-singlet conversion that eventually exposes dyes to singlet oxygen photodegradation