Water transfer and crack regimes in nano-colloidal gels

International audienceDirect observations of the surface and shape of model nano-colloidal gels associated with measurements of the spatial distribution of water content during drying show that air starts to significantly penetrate the sample when the material stops shrinking. We show that whether the material fractures or not during desiccation, as air penetrates the porous body, the water saturation decreases but remains almost homogeneous throughout the sample. This air-invasion is at the origin of another type of fracture due to capillary effects; these results provide a new insight in the liquid dynamics at the nano-scale. PACS number(s): 47.56.+r, 68.03.Fg, 81.40.N

Analysis of water content in wood material through 1D and 2D 1H NMR relaxometry: application to te the determination of the dry mass of wood

International audienceThere is an increasing interest on wood as it is an environmentally sustainable product (e.g. biodegradable and renewable). Thus, an accurate characterisation of wood properties is of extreme importance as they define the kind of application for which each type of wood can be used. For instance, dry mass of wood is a key parameter itself and is needed to calculate Moisture Content (MC) of wood, which is correlated to its physical properties. Due to the limitations of commonly used drying methods, preliminary work has shown the potential of 1H NMR to measure dry mass of wood but it has never been validated. Here, we performed a critical analysis of 1D and 2D 1H NMR relaxometry methods for obtaining the dry mass of wood and we compared their performance to three commonly used drying methods. This showed that commonly used drying methods do not remove all water from wood. Moreover, we are able to classify them accordingly to their performance. In addition, we showed that MC values obtained by 1H NMR relaxometry methods are higher (up to 20%) than values from commonly used drying methods. This empathizes the importance of accurate values of dry mass of wood and the utility of 1H NMR relaxometry on wood sciences. When comparing both NMR relaxometry methods, 2D should provide the more accurate results but 1D measurements would also be a recommended choice as they are faster than 2D and their results clearly overcome commonly used drying methods in a non-invasive and non-destructive manner

Correction to “Experimental Verification of Force Fields for Molecular Dynamics Simulations Using Gly-Pro-Gly-Gly”

Correction to “Experimental Verification of Force Fields for Molecular Dynamics Simulations Using Gly-Pro-Gly-Gly

Etude de l'effet d'un traitement thermique modéré sur l'hygroscopicité du bois par relaxométrie RMN du proton

International audienceLe bois, en tant que matériau de construction, est un matériau pertinent tant pour les bâtiments neufs que pour la rénovation d’anciennes bâtisses. Le patrimoine bâti montre que le bois permet de concevoir des monuments sains et durables. Pour toutefois estimer les durées de vie ou proposer des méthodes d'entretien ou de rénovation, il est nécessaire de poursuivre les efforts de recherche pour comprendre les mécanismes du vieillissement physique du bois et leurs effets sur ses propriétés hygro-mécaniques à l'échelle de ses constituants.Le but de cette étude est d'évaluer la relation entre la perte d'eau et le comportement hygroscopique de la structure de la paroi cellulaire avant et après un traitement thermique modéré. Par conséquent, la relaxométrie par résonance magnétique nucléaire du proton (1H RMN) est utilisée pour détecter l'eau liée dans les parois cellulaires du bois. Cette méthode gagne en popularité dans le domaine de la recherche car elle est non invasive, non destructive et permet d'étudier le même matériau soumis à différentes sollicitations. Ici, nous étudions l'état de l'eau adsorbée sur les parois cellulaires du bois grâce à la relaxométrie RMN 1H à faible champ (LF)

Présentation d’un projet PEPS CNRS : GREENWOOD

National audienceLe séchage du bois représente une dépense énergétique importante qui va s’amplifier avec le développement du bois dans la construction. L’enjeu de ce projet est de réaliser une étude sur l’utilisation du bois vert, c’est à dire jamais séché, dans la construction. Les bâtiments en bois datant du Moyen Age, basés sur ce procédé, nous prouvent la longévité des structures mises en œuvre à partir du bois vert. La problématique réside dans le respect des déformations admissibles des poutres de bois vert soumises à des chargements mécaniques et climatiques variables ainsi que dans les techniques d’assemblage pertinentes pour les structures. Une meilleure connaissance du comportement hygro-mécanique du bois vert pourrait permettre de proposer des innovations constructives

Novel Experimental–Modeling Approach for Characterizing Perfluorinated Surfactants in Soils

Novel Experimental–Modeling Approach for Characterizing Perfluorinated Surfactants in Soil

Investigation of the effect of aging on wood hygroscopicity by 2D 1 H NMR relaxometry

International audience2D 1 H NMR relaxometry is increasingly used in the field of wood sciences due to its great potential in detecting and quantifying water states at the level of wood constituents. More precisely, in this study, this technique is used to investigate the changes induced by "natural" and "artificial" aging methods on modern and historical oak woods. Two bound water components are detected and present differences in terms of association to the different wood polymers in cell walls: one is more strongly associated to wood polymers than the other. The evolution of the two bound water types is discussed in regard to aging methods and is related to the structure of the cell wall, especially with the S2 layer and the evolution of wood chemical composition (cellulose, hemicelluloses and lignin). The evolution of hydric strains is discussed taking into account the effect of aging methods on the two bound water components too. The obtained results confirm the ability of 2D NMR relaxomety to evaluate the effect of aging at the molecular level and on hydric deformation. Furthermore, this method shows that it is possible to determine the moisture content of wood without the necessity to oven-dry the wood material

Reversible and irreversible effects of a moderate heat treatment on the moisture sorption and swelling behavior of modern and historical oak wood

International audienceThe reversibility of a moderate thermal treatment (TT) at 120 °C on modern and historical oak wood samples was investigated by 1H nuclear magnetic resonance (NMR) relaxometry, equilibrium moisture content (EMC) determination, and measurements of volumetric deformations. The EMC values showed full reversibility after conditioning the samples at 65% relative humidity (RH) for one week, in agreement with previous research that utilized moderate TTs. However, 1H NMR relaxometry evidenced an irreversible effect on water mobility (i.e., molecular tumbling) for both wood samples. This result is compared to volumetric deformations that are determined by considering two reference states. When using, as a reference, the dry volume at each state, volumetric deformations are consistent with EMC values. However, when using the dry volume of the sample before TT, the volumetric deformations are found to be higher than the ones before TT for modern wood but remain lower for historical wood. The irreversible changes in water dynamics suggest that some modifications of the wood structure have not been completely recovered but are not linked to the changes in volumetric deformations. In addition, 13C solid-state NMR spectroscopy allowed the comparison of the composition between both wood samples, suggesting that their different behavior concerning volumetric deformations could be explained by a lower proportion of acetyl groups from hemicelluloses for historical wood due to its natural aging. We showed that combining macroscopic observations with molecular-level information gained from 1H and 13C NMR leads to a deeper understanding of the effects of thermal treatments and reversibility tests

Mechanisms of liquid transport in softwood inferred from Magnetic Resonance Imaging

National audienceWater in wood material plays a major role with regard to its mechanical or physical properties in various situations, in particular in outdoor applications, leading to a possible deterioration in the performance of the wood elements (eg. structural integrity, thermal insulation). Therefore, it is crucial to understand the water uptake and release as well how the water transports in the wood material to extend the lifetime of the timber buildings. The mechanisms of liquid transport are related to the hierarchical and multi-scale structure of wood and to the presence of free and bound water. Despite numerous studies, the water migration process in wood material is not well understood. For this study, softwood materials used in construction are subjected to imbibition tests. Through an original approach coupling quantitative information obtained from mass and deformation measurements, Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging, we are able to quantify bound and free water, which finally allows to better understand imbibition mechanisms. Additional experiments with oil (dodecane) allow to compare the characteristics of water imbibition with those of a liquid not hygroscopically adsorbed in wood