Spontaneous gelation of wheat gluten proteins in a food grade solvent

Structuring wheat gluten proteins into gels with tunable mechanical properties would provide more versatility for the production of plant protein-rich food products. Gluten, a strongly elastic protein material insoluble in water, is hardly processable. We use a novel fractionation procedure allowing the isolation from gluten of a water/ethanol soluble protein blend, enriched in glutenin polymers at an unprecedented high ratio (50%). We investigate here the viscoelasticity of suspensions of the protein blend in a water/ethanol (50/50 v/v) solvent, and show that, over a wide range of concentrations, they undergo a spontaneous gelation driven by hydrogen bonding. We successfully rationalize our data using percolation models and relate the viscoelasticity of the gels to their fractal dimension measured by scattering techniques. The gluten gels display self-healing properties and their elastic plateaus cover several decades, from 0.01 to 10000 Pa. In particular very soft gels as compared to standard hydrated gluten can be produced.Comment: Food Hydrocolloids, in pres

Unexpected spatial distribution of bubble rearrangements in coarsening foams

Foams are ideal model systems to study stress-driven dynamics, as stress-imbalances within the system are continuously generated by the coarsening process, which unlike thermal fluctuations, can be conveniently quantified by optical means. However, the high turbidity of foams generally hinders the detailed study of the temporal and spatial distribution of rearrangement events, such that definite assessments regarding their contribution to the overall dynamics could not be made so far. In this paper, we use novel light scattering techniques to measure the frequency and position of events within a large sample volume. As recently reported (A. S. Gittings and D. J. Durian, Phys. Rev. E, 2008, 78, 066313), we find that the foam dynamics is determined by two distinct processes: intermittent bubble rearrangements of finite duration and a spatially homogeneous quasicontinuous process. Our experiments show that the convolution of these two processes determines the age-dependence of the mean dynamics, such that relations between intermittent rearrangements and coarsening process can not be established by considering means. By contrast the use of the recently introduced photon correlation imaging technique (A. Duri, D. A. Sessoms, V. Trappe, and L. Cipelletti, Phys. Rev. Lett., 2009, 102, 085702) enables us to assess that the event frequency is directly determined by the strain-rate imposed by the coarsening process. Surprisingly, we also find that, although the distribution of successive events in time is consistent with a random process, the spatial distribution of successive events is not random: rearrangements are more likely to occur within a recently rearranged zone. This implies that a topological rearrangement is likely to lead to an unstable configuration, such that a small amount of coarsening-induced strain is sufficient to trigger another event

Unexpected drop of dynamical heterogeneities in colloidal suspensions approaching the jamming transition

As the glass (in molecular fluids\cite{Donth}) or the jamming (in colloids and grains\cite{LiuNature1998}) transitions are approached, the dynamics slow down dramatically with no marked structural changes. Dynamical heterogeneity (DH) plays a crucial role: structural relaxation occurs through correlated rearrangements of particle ``blobs'' of size $\xi$\cite{WeeksScience2000,DauchotPRL2005,Glotzer,Ediger}. On approaching these transitions, $\xi$ grows in glass-formers\cite{Glotzer,Ediger}, colloids\cite{WeeksScience2000,BerthierScience2005}, and driven granular materials\cite{KeysNaturePhys2007} alike, strengthening the analogies between the glass and the jamming transitions. However, little is known yet on the behavior of DH very close to dynamical arrest. Here, we measure in colloids the maximum of a ``dynamical susceptibility'', $\chi^*$, whose growth is usually associated to that of $\xi$\cite{LacevicPRE}. $\chi^*$ initially increases with volume fraction $\phi$, as in\cite{KeysNaturePhys2007}, but strikingly drops dramatically very close to jamming. We show that this unexpected behavior results from the competition between the growth of $\xi$ and the reduced particle displacements associated with rearrangements in very dense suspensions, unveiling a richer-than-expected scenario.Comment: 1st version originally submitted to Nature Physics. See the Nature Physics website fro the final, published versio

Impact of fluidized bed granulation on structure and functional properties of the agglomerates based on the durum wheat semolina

The granulation step determines the production yield and the final characteristics of the agglomerated couscous grains of durum wheat. The objective of the present work was to explore the capability of the fluidised bed technology to produce agglomerates of durum wheat semolina. The impacts of different processing conditions have been investigated on the structure and functional properties of the agglomerates. The size, shape, water content, compactness, and mechanical strength of the granules were measured. The fluidized bed agglomeration process has been found to produce agglomerates of durum wheat with different attributes compared to those produced by granulation using the low shear mixers. The results were discussed in regard to the hydro-textural approach, in order to get a better understanding of the mechanisms and relationships between process, structure, and properties. Two major agglomeration mechanisms contribute to the growth of the wet agglomerates: a fractal-structuring process followed by a phenomenon of densification. By studying the evolution of the compactness, diameter and water content, it was demonstrated that inter granular arrangements led to an expansion followed by a densification of the wet agglomerates. A relationship was proposed to describe the growth using a fluidized bed of the wet agglomerates of durum wheat semolina

Time Resolved Correlation measurements of temporally heterogeneous dynamics

Time Resolved Correlation (TRC) is a recently introduced light scattering technique that allows to detect and quantify dynamic heterogeneities. The technique is based on the analysis of the temporal evolution of the speckle pattern generated by the light scattered by a sample, which is quantified by $c\_I(t,\tau)$, the degree of correlation between speckle images recorded at time $t$ and $t+\tau$. Heterogeneous dynamics results in significant fluctuations of $c\_I(t,\tau)$ with time $t$. We describe how to optimize TRC measurements and how to detect and avoid possible artifacts. The statistical properties of the fluctuations of $c\_I$ are analyzed by studying their variance, probability distribution function, and time autocorrelation function. We show that these quantities are affected by a noise contribution due to the finite number $N$ of detected speckles. We propose and demonstrate a method to correct for the noise contribution, based on a $N\to \infty$ extrapolation scheme. Examples from both homogeneous and heterogeneous dynamics are provided. Connections with recent numerical and analytical works on heterogeneous glassy dynamics are briefly discussed.Comment: 19 pages, 15 figures. Submitted to PR

Etude des propriétés mécaniques par nanoindentation de systèmes couche organominérale/substrat

Il n'y a pas la page de garde, l'introduction et la conclusion du manuscrit car je ne les retrouve pas.Maste

Dynamique spatialement et temporellement hétérogène dans la relaxation lente de la matière molle vitreuse

We have investigated dynamical heterogeneities in the slow relaxation of soft glassy systems, using some novel multispeckle light scattering techniques. The first technique, called “Time Resolved Correlation” (TRC), allows one to characterize temporally heterogeneous dynamics. We have optimized TRC working on a model system, a foam. We have proposed several methods to correct from the statistical objects characterising the fluctuations of the dynamics (variance, probability density function, and autocorrelation) the noise contribution due to the finite number of pixel of the CCD camera. The second technique, called “Space and Time Resolved Correlation” (STRC), allows one to characterize spatially heterogeneous dynamics. Thanks to STRC, we have shown that the dynamics of a concentrated lamellar vesicle gel and that of strongly attractive colloidal gel is correlated over surprisingly long distances. Additional measurements on the colloidal gel, performed in a wide range of scattering vectors, have highlighted the dependence of the average dynamics and of its temporally fluctuations with the probed length scale. We proposed a simple model, based on a serie of rearrangements events correlated spatially and random in time, that accounts for the observed behavior.Ce travail est consacré à l’étude des hétérogénéités dynamiques dans la relaxation lente de la matière molle vitreuse par des techniques originales de diffusion de la lumière multispeckle, développées au cours de cette thèse. La première technique, appelée « Corrélation Résolue dans le Temps » (TRC), permet de caractériser les hétérogénéités temporelles de la dynamique. Elle a été optimisée en considérant un système modèle, les mousses. Nous avons proposé diverses méthodes pour supprimer la contribution du bruit de la mesure, due au nombre limite de pixels de la camera CCD, dans des objets statistiques caractérisant les fluctuations de la dynamique (variance, fonction densité de probabilité et autocorrélation). La deuxième technique, appelée « Corrélation Résolue dans le Temps et dans l’Espace » (STRC), permet de caractériser les hétérogénéités spatiales de la dynamique. Grâce à la STRC, nous avons montré que la dynamique d’un gel concentré de vésicules lamellaires et celle d’un gel colloïdal fortement attractif sont, de façon surprenante, corrélées sur des distances très longues. Des mesures complémentaires sur le gel colloïdal, effectuées à plusieurs vecteurs de diffusion, ont mis en évidence la dépendance de la dynamique moyenne et de ses fluctuations temporelles avec la longueur sondée. Nous avons établi un modèle simple, basé sur une série de réarrangements corrélés spatialement et aléatoires dans le temps, qui est en accord avec les résultats expérimentaux

Mesures rhéologiques sur la grave émulsion de bitume par propagation d’ondes acoustiques

il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATIONMesures rhéologiques sur la grave émulsion de bitume par propagation d’ondes acoustique

Long range correlations and intermittency in the slow dynamics of a soft glass

International audienc

Une représentation de la phénoménologie des milieux granulaires humides : entre mobilités granulaires et interactions entre phases

International audienceLes milieux granulaires humides sont le siège d’une phénoménologie riche et complexe à appréhender. En ce sens,ils représententun « territoire » d’expérimentations et de modélisationsdont l’exploration se justifie pleinement par la nécessité d’en maitriser au mieux leurs multiples usages. La diversitédes mélangesmultiphasiques généréspar l’humidification de granulaires se caractérisenotamment par des comportements spécifiquesen fonction des quantitésrelatives et de la connexitéde chacune des phases, avec une forte modulation selon les contraintes externes appliquées. Deux caractéristiques majeures de ces milieux hétérogènes dispersés à structure divisée font l’objet d’études que nous menons dans le laboratoire d’Ingénieriedes Agropolymères et Technologies Emergentes. La première caractéristique porte sur l’identification et la modélisation des typologies de mobilité granulaire, lorsque le milieu est soumis à des contraintes mécaniques promues par un intrant mécanique (malaxeur, intrudeur...). A partir d’une expérience de rhéophysique qui permet de quantifier la résultante des efforts au niveau d’un intrudeur ainsi que le champ de vitesses par PIV d’un lit de particules ensilées, les écoulements sont caractérisés. Ces travaux sont pour le moment conduit sur des matériaux secs. La seconde caractéristique s’intéresse à appliquer leconcept de diagramme de phases, initialement défini pour les milieux «thermiques» (colloïdes, macromolécules),aux milieux granulaires humides (athermiques) afin de les représenter de façon génériqueles états issus des interactions entre les phasesen présence. Cette représentation offre la possibilité de situer les états au cours de la transformation du milieux granulaires par différentstypes de procédés:opérationsde mélange,de mise en forme, de transferts de matièreavecou sans changements de phases. L’exposé illustrera succinctement les applications de ce concept au cas de l’agglomérationhumide et du séchag