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Water sorption and dynamical properties of bread crust were studied using gravimetric sorption experiments. Water uptake and loss were measured while relative humidity (RH) was step-wise in- or decreased. Experimental results were compared with Fickian diffusion models and empirical models like the exponential and power-law model. From comparison of experimental sorption curves and the power-law model for short times it followed for all bread crust that the diffusional coefficient n is close to one. It turned out that this is not due to so-called case II diffusion and water transport that is limited by relaxation of the solid material but due to the fact that RH did not instantaneously but gradually increased to the set value. Sorption curves of isotherm experiments could be best described by the Fickian diffusion model for low RH and by the exponential model for large RH. Transport rates depend on moisture content and show a maximum around RH = 0.7, corresponding to a water mass fraction ω1 = 0.12. Diffusion rates could be well described by free volume theory up to the maximum, but this theory could not explain the strong decrease at higher ω1. Indications for a local glass-rubber transition at room temperature were found near a water mass fraction ω1 ≈ 0.09. This corresponds very well to the start of the crisp–non-crisp transition as measured by a sensory panel, but not to the glass-rubber transition at ω1 ≈ 0.12 as measured by other techniques like Differential Scanning Calorimetry. So it seems that more than one glass-rubber like transitions may be important to describe the properties of heterogeneous cellular food systems.

Food structuring is discussed from the viewpoints of soft matter physics and molecular gastronomy. Food is one of the most complex types of soft matter, with multiple dispersed phases and even hierarchical structure. Food structuring seems to be a kind of art, comprising a careful balance between forces driving the system towards equilibrium and arresting forces. A more scientific approach to this complex matter is desirable, using (1) concepts from soft matter physics, e.g. free energy and jamming, and (2) complex disperse system (CDS) notation as developed for molecular gastronomy. Combining CDS with state diagrams renders a new tool for the qualitative description of the complex process of making structured foods.

The dynamical susceptibility has been introduced to characterize the dynamical heterogeneities in glass forming liquids. We have used it as a tool to investigate the slow dynamics of other disordered systems such as gels, granular media and spin glasses. We review here the results obtained via numerical simulations of different model systems. The comparative study of the behaviour of the dynamical susceptibility sheds some light on the significant differences in the complex slow dynamics of glasses, spin glasses, granular media, irreversible gels, and colloidal gels.

Through elastic neutron scattering measurements, we investigated the picosecond dynamics of DNA in the hydrated powder state or embedded in glycerol glassy matrix from 20 K to 300 K. We calculated the relaxational contribution of the mean square displacements (MSD) of DNA hydrogen atoms. We found the existence of a linear relationship between the inverse of the biomolecule relaxational MSD and the logarithm of the bulk viscosity of the surrounding environment. From the comparison with the case of lysozyme in the same environments, for which the validity of the relationship was already verified, possible differences and analogies concerning the biomolecule-to-solvent dynamical coupling can be stressed. (C) 2007 Elsevier B.V. All rights reserved.

International audience; A series of cholinium cation-based bioionic liquids (BioILs) were synthetized with the aim of screening their performance as potential plasticizers of thermoplastic starch. To synthesize these BioILs, two easy and fast synthetic routes were selected: an ion exchange reaction, direct and economical, and a two-step acid-base reaction. Most of these BioILs allowed efficient plasticization of starch by film casting. The structure of the anion used significantly influences the thermo(hygro) mechanical and recrystallization behavior, making it possible to modulate the properties of the final material.

The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics for describing supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different than the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition are qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order-like phase transition between out-of-equilibrium states., Comment: 29 pages, 8 figures

It is well accepted that adding nanoparticles (NPs) to polymer melts can result in significant property improvements. Here we focus on the causes of mechanical reinforcement and present rheological measurements on favourably interacting mixtures of spherical silica NPs and poly(2-vinylpyridine), complemented by several dynamic and structural probes. While the system dynamics are polymer-like with increased friction for low silica loadings, they turn network-like when the mean face-to-face separation between NPs becomes smaller than the entanglement tube diameter. Gel-like dynamics with a Williams–Landel–Ferry temperature dependence then result. This dependence turns particle dominated, that is, Arrhenius-like, when the silica loading increases to ∼31 vol%, namely, when the average nearest distance between NP faces becomes comparable to the polymer’s Kuhn length. Our results demonstrate that the flow properties of nanocomposites are complex and can be tuned via changes in filler loading, that is, the character of polymer bridges which ‘tie’ NPs together into a network., Partial support has been provided by the EU FP7 (ETN Supolen GA-607937, Infrastructure ESMI GA-262348) and the Greek General Secretariat for Research and Technology (Thalis-380238 COVISCO). M.R. acknowledges financial support from the National Science Foundation under grants DMR-1309892, DMR-1436201 and DMR-1121107, the National Institutes of Health under grants P01-HL108808 and 1UH2HL123645 and the Cystic Fibrosis Foundation. D.Z., S.G., R.H.C. and S.K.K. gratefully acknowledge the National Science Foundation grant DMR-1408323 for financial support.

The crystallization kinetics of phase-change materials (PCMs) entails a crucial aspect of phase-change memory technology, and their study is also of interest to advance the understanding of crystallization in general. Research on crystallization of PCMs remains challenging because of the short (nanosecond) time and small (nanometer) length scales involved. Ultrafast differential scanning calorimetry (DSC) offers a powerful tool to study crystallization via ultrahigh heating rates. Here, we used this tool to study the crystallization kinetics of growth-dominant Ge7Sb93. Two models describing the viscosity of the undercooled liquid were used to interpret the data and were subsequently crosschecked by independent growth-rate data. With both models the data in Kissinger plots could be fitted well, but one of the models resulted in a large discrepancy with the independent data. These results demonstrate that great care is needed when deriving crystal-growth rates from ultrafast DSC measurements because orders of magnitude errors can be made. The present analysis showed a slightly non-Arrhenius crystallization behavior for the Ge7Sb93 alloy, corresponding to a fragility of 65 and a glass transition temperature of 379 K. The overall viscosity and growth rate of this alloy between the glass and melting temperatures have been revealed, as well as a maximum growth rate of 21 m s(-1) at similar to 800 K. Models based on ultrafast DSC data offer interpretation of crystallization kinetics of PCMs and thereby strongly support the design of PCMs for memory applications.

International audience; We use large scale molecular dynamics simulations to investigate the relation between cooperativity and size effects in a simple diatomic supercooled liquid. We find that below a characteristic temperature the transport properties depend on the size of the simulation box. This effect then increases upon decreasing the temperature. For the model molecules constituting our liquid, the smaller box corresponds to the larger diffusion coefficient. Thus, the size effects increase the diffusion of the liquid with our molecules in opposition with previous results concerning silica and atomic soft molecules. As a result, the temperature dependence of the diffusion coefficient tends to an Arrhenius law for smaller boxes in our simulations. This result is in agreement with a cooperativity origin of non-Arrhenius behavior and size effects in fragile supercooled liquids, as a small box cutoff cooperative motions thus inducing a constant activation energy. To investigate that picture further we then study the size dependence of cooperative motions in our model liquid.

International audience; During cryopreservation ice nucleation and crystal growth may occur within cells or the intracellular compartment may vitrify. Whilst previous literature describes intracellular vitrification in a qualitative manner, here we measure the intracellular vitrification temperature of bacteria and yeasts under conditions relevant to cryopreservation, including the addition of high levels of permeating and nonpermeating additives and the application of rapid rates of cooling. The effects of growth conditions that are known to modify cellular freezing resistance on the intracellular vitrification temperature are also examined. For bacteria a plot of the activity on thawing against intracellular glass transition of the maximally freeze-concentrated matrix (Tg’) shows that cells with the lowest value of intracellular Tg’ survive the freezing process better than cells with a higher intracellular Tg’. This paper demonstrates the role of the physical state of the intracellular environment in determining the response of microbial cells to preservation and could be a powerful tool to be manipulated to allow the optimization of methods for the preservation of microorganisms.

A Brillouin scattering investigation has been carried out on trehalose-water solutions in a wide range of concentrations (0 < phi < 0.74) in the ultraviolet regime. A complete set of data as a function of temperature (-10 degrees C

International audience; Brillouin light and x-ray scattering have been used to investigate the dynamic structure factor of supercooled and glassy m-toluidine in the temperature range between 34 and 303 K. In addition to the obiquitous α relaxation, evidence is given of a fast relaxation process active in the ns-ps time region. Information on the activation energy of the fast process is obtained from the attenuation of longitudinal acoustic modes.

We employ dielectric spectroscopy to monitor the relaxation dynamics and crystallization kinetics of the Biclotymol antiseptic in its amorphous phase. The glass transition temperature of the material as determined by dielectric spectroscopy is Tg = 290 ± 1K. The primary (α) relaxation dynamics is observed to follow a Vogel-Fulcher-Tammann temperature dependence, with a kinetic fragility index m = 86 ± 13, which classifies Biclotymol as a relatively fragile glass former. A secondary relaxation is also observed, corresponding to an intramolecular dynamic process of the non-rigid Biclotymol molecule. The crystallization kinetics, measured at four different temperatures above the glass transition temperature, follows an Avrami behavior with exponent virtually equal to n = 2, indicating one-dimensional crystallization into needle-like crystallites, as experimentally observed, with a time-constant nucleation rate. The activation barrier for crystallization is found to be Ea = 115 ± 22 kJ mol(-1).

Presenting simple coarse-grained models of isotropic solids and fluids in $d=1$, $2$ and $3$ dimensions we investigate the correlations of the instantaneous pressure and its ideal and excess contributions at either imposed pressure (NPT-ensemble, $\lambda=0$) or volume (NVT-ensemble, $\lambda=1$) and for more general values of the dimensionless parameter $\lambda$ characterizing the constant-volume constraint., Comment: 17 pages, 9 figures

The dynamics of the human oligonucleotide AG 3(T2 AG 3)3 has been investigated by incoherent neutron scattering in the sub-nanosecond timescale. A hydration-dependent dynamical activation of thermal fluctuations in weakly hydrated samples was found, similar to that of protein powders. The amplitudes of such thermal fluctuations were evaluated in two different exchanged wave-vector ranges, so as to single out the different contributions from intra- and inter-nucleotide dynamics. The activation energy was calculated from the temperature-dependent characteristic times of the corresponding dynamical processes. The trends of both amplitudes and activation energies support a picture where oligonucleotides possess a larger conformational flexibility than long DNA sequences. This additional flexibility, which likely results from a significant relative chain-end contribution to the average chain dynamics, could be related to the strong structural polymorphism of the investigated oligonucleotides.

Recently we have studied, using numerical simulations, a limited valency model, i.e. an attractive square well model with a constraint on the maximum number of bonded neighbors. Studying a large region of temperatures $T$ and packing fractions $\phi$, we have estimated the location of the liquid-gas phase separation spinodal and the loci of dynamic arrest, where the system is trapped in a disordered non-ergodic state. Two distinct arrest lines for the system are present in the system: a {\it (repulsive) glass} line at high packing fraction, and a {\it gel} line at low $\phi$ and $T$. The former is essentially vertical ($\phi$-controlled), while the latter is rather horizontal ($T$-controlled) in the $(\phi-T)$ plane. We here complement the molecular dynamics results with mode coupling theory calculations, using the numerical structure factors as input. We find that the theory predicts a repulsive glass line -- in satisfactory agreement with the simulation results -- and an attractive glass line which appears to be unrelated to the gel line., Comment: 12 pages, 6 figures. To appear in J. Phys. Condens. Matter, special issue: "Topics in Application of Scattering Methods for Investigation of Structure and Dynamics of Soft Condensed Matter", Fiesole, November 2005

In this paper we predict the water activity and initial freezing point of food products (meat and fish) based on their composition. The prediction is based on thermodynamics (the Clausius–Clapeyron equation, the Ross equation and an approximation of the Pitzer equation). Furthermore, we have taken the effect of bound water into account, by using a linear relation between mass fractions of bound water and the mass fractions of soluble biopolymers. Model parameters are estimated using data of meat. The validity of the model is checked against data of fish. Good agreement with experimental data are obtained in the range of aw > 0:70. Furthermore, our results remove the inconclusiveness on the prediction of bound water that exists in literature. 2004 Elsevier Ltd. All rights reserved.

Both structural unfreezing and irreversible endothermic change between different molecular states of a material can occur on heating its liquid state and produce a double sigmoid-shaped endotherm in its apparent heat capacity, C-p. In such a case, the usual calorimetry is unable to distinguish between the molecular mechanisms of the two endothermic contributions. We report that this distinction can be made by measuring C-p and the complex heat capacity, C-p(*), simultaneously in a temperature-modulated scanning mode. When a sigmoid- shaped increase is observed in both C-p and C-p* of a liquid, the underlying process is structural unfreezing. P But, when this increase is observed in normal scanning and not in the temperature-modulated mode, the underlying process is either irreversible or too slow, compared to the modulation period. The method has been used for resolving the nature of tautomeric transformation in liquid beta-D-fructose. Simultaneous C-p and C-p(*) measurements show that, for normal scannin, C-p increases in a sigmoid-shaped manner with hysteresis, P 9 but for temperature-modulated scanning, the real component of C-p does not increase in this manner (i.e., the reversible component of the heat flow shows neither a sigmoid-shaped increase nor hysteresis). Therefore, the sigmoid-shaped C-p increase observed in normal scanning indicates an endothermic transformation in the beta-D-fructose liquid at T > T-g and not unfreezing of tautomeric transformation on the time scale of heating.

In recent molecular dynamics simulations [Phys. Rev. E 2003, 68, 061508] we found that the deviation of the single-particle displacement distribution from Gaussian form is a characteristic that is common to all phases of a system confined to a quasi-two-dimensional geometry (liquid, hexatic, and solid). These deviations, which intensify with increasing density and/or decreasing temperature, are a consequence of correlated particle motion and are related to the emergence of a third dynamical relaxation mode in the intermediate time regime. It was suggested that this collective motion is generated by superpositions of instantaneous normal mode vibrations along diffusive paths. The diffusive paths are along the directions with strong bond-orientation correlation and start to grow in amplitude rapidly on entry into the hexatic phase. In this paper we report the results of a study of the relation between the distribution of the instantaneous normal mode frequencies and the observed cooperative dynamics. We find that as the temperature decreases the distribution of the instantaneous normal mode frequencies (the real and the imaginary parts) shifts to lower frequency and the deviations of the single-particle displacement distribution from Gaussian form increase. The results indicate that there is a relationship between the average time at which the cooperative dynamics of the system is maximum, , and the average value of the squared frequency for which the spectrum of the imaginary 2 2 normal modes is maximum, , that has the form ln = ln (-1) + c(rho), where c(rho) is a density dependent constant.

Literature on the crispy / crunchy behaviour of cellular solid foods with a crust is discussed. The emphasis is on products with a dry crispy or crunchy crust as bread and various snacks and especially on mesoscopic and macroscopic aspects. Successively, the sensory sensation involved, the relation to fracture behaviour, morphological aspects, and the relation between crispy and crunchy behaviour and mobility of the macromolecules and plasticizer (primarily water) involved, are discussed. Finally we will discuss some ideas for an integrated approach of crispy / crunchy behaviour of cellular solid foods with a dry crust.

International audience; Amorphous polymers in their glass transition regime can be described as a tiling of nanometric domains. Each domain exhibits its own relaxation time, which is distributed over at least four decades. These domains are known as dynamical heterogeneities. This article describes the mechanics of amorphous polymers using a stochastic continuum mechanics model that includes their heterogeneous dynamics. Solving this model both by finite elements and by using a self-consistent method, we find a viscoelastic relaxation spectrum quantitatively similar to an experimentally measured spectrum in a polymer. We show evidence that elastic couplings between domains control the stress relaxation after a step strain and result in a narrowing of the long-time region of the viscoelastic spectrum (as compared to that of dynamical heterogeneities).

The production of bioplastics directly from wheat flour has been demonstrated to be reliable, but scarce knowledge is available on how flour characteristics may affect the performance of thermoplastic films. In this work, we first established the most suitable recipe and process for the production of extruded films and then we used eight single-cultivar wheat flours with different baking technological properties to assess how they affect the mechanical properties of thermoplastic films. The results have shown that flours from soft grain cultivars offered more rigid and deformable films than flours from hard grain cultivars. For similar hardness, the alveographic P/L ratio of the dough was inversely related to rigidity and directly related to deformability of plastic films, while the deformation energy of the dough (W) played a role only for great differences of it. The subsequent fabrication of blends between each of the flours that yielded the best film properties and polycaprolactone (PCL) at different proportions indicated that a wheat flour/PCL ratio (TWF/PCL) of 75/25 offered the most suitable films for further application. Our results are likely to be useful for improving the plasticization of flour, in that selection of wheat flours could be tailored on the properties desired for the bioplastic films.

We consider various initial-value problems for ordinary integro-differential equations of first order that are characterized by convolution-terms, where all factors depend on the solutions of the equations. Applications of such problems are descriptions of certain glass-transition phenomena based on mode-coupling theory, for instance. We will prove results concerning well-posedness of such problems and the asymptotic behaviour of their solutions.

International audience; Poly (butyl methacrylate-co-methacrylic acid) copolymers/calcium carbonate (CaCO3) composites were synthesized by radical polymerization. Ca2+ cationic sites, present at the CaCO3 surface, in interaction with carboxylate groups from polymer chains structured the material, particularly above the glass transition temperature. The composites were studied by transmission electron microscopy, X-ray diffraction, and dynamic mechanical analysis. Multiplets and clusters were detected. The material's behavior is principally controlled by the methacrylic acid (MA) content in the copolymer chain and CaCO3/MA ratio. Under well-defined conditions, ionic cross-linked materials were obtained.

Molecular dynamics simulations are used to generate an ensemble of saddles of the potential energy of a Lennard-Jones liquid. Classifying all extrema by their potential energy u and number of unstable directions k, a well defined relation k(u) is revealed. The degree of instability of typical stationary points vanishes at a threshold potential energy, which lies above the energy of the lowest glassy minima of the system. The energies of the inherent states, as obtained by the Stillinger-Weber method, approach the threshold energy at a temperature close to the mode-coupling transition temperature Tc., Comment: 4 RevTeX pages, 6 eps figures. Revised version

The objective of the present work is to get insights into the mechanistic origin of the reinforcement effects of nanoclay on a segmented polybutadiene polyurethane-urea system. To this end, a convergent analysis of the hard domain morphology and conformational state of soft segment in the nanocomposites was carried out by using a combination of complementary characterization techniques, namely, Fourier transform infrared spectroscopy, small angle neutron scattering, transmission electron microscopy, modulated differential scanning calorimetry and dynamic mechanical analysis. Analysis of small angle neutron scattering data by a combination of Percus-Yevick hard sphere and Zernike-Ornstein model coupled with direct visualization of the dispersed hard domain morphology from transmission electron microscopy provided insight on clay induced changes in the hard domain morphology. A monotonic decrease in the domain size as well as the average interdomain distance was observed with increasing nanoclay content in the polymer matrix. Analysis of the carbonyl stretching region from FTIR showed increased degree of hydrogen bonding for the urethane carbonyl groups of the nanocomposites compared to the neat matrix. A combination of calorimetric and dynamic mechanical analysis revealed the existence of a constrained amorphous region; quantified to be approximate to 16% at the highest clay content experimented. The manifestation of these morphological and conformational changes on the nano-, micro- and macro scale reinforcements in the nanocomposites was investigated by mechanical properties at these length scales using nanoindentation, DMA and tensile testing, respectively. (C) 2014 Elsevier Ltd. All rights reserved.

Electrostatic separation based on different tribo-electric charging behaviours of components has emerged as a novel, sustainable dry fractionation process. This study aims to characterise charging behaviour of single-component particles in nitrogen gas flowing through aluminium tubes. Experiments were carried out with polystyrene (PS) particles and wheat gluten as model particles. Results indicated that specific charge increased linearly with gas velocity up to 28 m/s for both materials. It was found that surface charge densities of different-sized PS particles overlapped for laminar gas flow, whereas for higher stronger gas flow rates, surface charge density of the smallest particles deviated from that of larger particles. Specific charge of PS particles increased linearly with increasing tube length from 125 to 225 mm. Additionally, charging of PS particles was unaffected by relative humidity (RH) of gas; however, specific charge of wheat gluten decreased for RH > 80%. Concluding, these results provide insight in critical parameters affecting charging behaviour, thus facilitating the development of electrostatic separation processes to fractionate food ingredients.

Facilitated spin models were introduced some decades ago to mimic systems characterized by a glass transition. Recent developments have shown that a class of facilitated spin models is also able to reproduce characteristic signatures of the structural relaxation properties of glass-forming liquids. While the equilibrium phase diagram of these models can be calculated analytically, the dynamics are usually investigated numerically. Here we propose a new network-based approach, called approximate master equation (AME), to the dynamics of the Fredrickson-Andersen model. The approach correctly predicts the critical temperature at which the glass transition occurs. We also find excellent agreement between the theory and the numerical simulations for the transient regime, except in close proximity of the liquid-glass transition. Finally, we analytically characterize the critical clusters of the model and show that the departures between our AME approach and the Monte Carlo can be related to the large interface between frozen and unfrozen spins at temperatures close to the glass transition., Comment: 10 pages, 5 figures, 2 tables

To develop n-type processable polymeric materials for photovoltaic applications, a series of polymers was synthe- sized by grafting fullerene C60 onto polystyrene (PS). Grafted polymers were studied and compared with PS:fullerene blends. Electronical and electrical properties were first measured to define the minimal amount of C60 required for solar cells applica- tion. Then, thermal properties and rheological behavior of grafted polymers were analyzed to determine whether they could be processed from the melt. A throughout experimental study revealed that C60-grafted polymers exhibit two thresholds. The first threshold at 3-4 vol % (detected by electrical conductiv- ity, electron mobility, and melt viscosity measurements) is asso- ciated to the percolation of C60 molecules. The second threshold (evidenced by glass transition and melt viscosity measurements and confirmed by optical and atomic force micrograph observa- tions) at about 12-13 vol % is assumed to be related to the for- mation of C60 aggregates. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000-000, 2012

In this paper we have analyzed the hydration properties of vegetable materials, namely carrots and mushrooms, by means of the Flory-Rehner theory. This is done to circumvent problems with the ill-defined concept of water holding capacity. Via this thermodynamic theory one can predict the hydration properties for a wide range of mechanical loads. The theory is compared to measurements on the hydration of the vegetable samples in centrifugation experiments. The theory predicts two contributions to the hydration properties, which are due to 1) mixing free energy of water and food ingredients, and 2) the elastic energy of the crosslinked network of cell wall materials (i.e. the dietary fibers). Via independent measurements of the moisture sorption isotherms, we have quantified of the mixing contribution, which can be described by the volume-averaged Flory-Huggins Free Volume theory. From combined analysis of centrifugation and sorption experiments, we have obtained the elastic contribution, which is shown to follows the Flory-Rehner theory. Remarkably, the cell wall materials of carrots and mushrooms show very similar elastic behavior. (C) 2013 Elsevier Ltd. All rights reserved.

Although many polymer nanocomposites have been described, the impact of colloidal nanoparticles (NPs) used as fillers on the thermal behavior of the matrix has been described only in a few cases. Here we apply thermal methods to inquire the effect of organically capped Ag and Au particles on poly(tert-butyl acrylate) (PtBA) based composites. The nanocomposites have been prepared by ex situ and in situ methods; in the former method the metal NPs were isolated from the respective colloids and then blended into cast films obtained from tetrahydrofuran solutions of the polymer; while in the latter the in situ polymerization of tert-butyl acrylate using miniemulsions was carried out in the presence of homogeneously dispersed colloidal NPs. The nanocomposite materials were then characterized by differential scanning calorimetry (DSC) to assess the effect of colloidal metal NPs on the glass transition temperature of the polymer (T-g) namely by considering their chemical nature, average particle size, and metal load. Although similar effects have been observed when Au or Ag NPs were employed as nanofillers, it was also found that the T-g depends on the NPs morphological characteristics and on the preparative method employed to obtain the nanocomposite. This research also highlights the relevance of the surface chemistry of colloidal nanofillers on the thermal behavior of the respective composites. (C) 2013 Elsevier B.V. All rights reserved.

Experimental results by Fisher et al. [Faraday Discuss. Chem. Soc. 1979, 68, 26] showed the existence of local orientational correlations of segments of the n-alkane molecules in the liquid state. Since the estimated correlation volume is below 10(3) angstrom(3), molecular dynamics simulations appear to be a suitable method for their identification and characterization. We used molecular dynamics to fully characterize short-range order in polyethylene melts. The characterization started by identifying sequences of aligned segments in chains, each one having at least one Kuhn monomer in length. Afterward, a search was made for interactions of a tagged aligned chain segment with others fulfilling the same condition, laying within a limiting separation distance (18 angstrom) and making a limiting orientation angle (40 degrees). When, at least, four interactions are counted, a short-range ordered region is defined. Chain placement in these regions has similarities to that of the unit cell at the solid phase, although with different separation distances and angle. Overall, short-range order resembles a dynamic uniaxial nematic phase, the local order parameter increasing with the chain length in agreement with experimental results. Segments at the ordered regions persist over time, for times longer than the Rouse relaxation time of the chain. Those in random conformational sequences between the ordered regions have a mass distribution in agreement with the Flory distribution, with a number-average value comparable to experimental results for the molecular mass between entanglements.

The main objective of the present work was to determine whether a single agropolymer [wheat gluten (WG)] could fit the modified atmosphere packaging (MAP) requirements of a range of six different fresh produce in key terms of oxygen permeation (PeO2) and CO2/O2 permselectivity (S) values. The required properties for optimal packaging of fresh fruits and vegetables were first evaluated using the Tailorpack MAP modelling software (UMR IATE, Montpellier, France) with packaging dimensions and respiratory and optimal atmosphere data as input parameters. Then, the modelled values obtained were compared with the properties of a range of WG composite films: monolayer self-supported or multilayer at microscale or nanoscale, cast or thermoplasticised, with different formulations (percentage of plasticisers or nanofillers). The experimental gas transfer properties that could be covered by these materials ranged from 0.05x1010 to 2.00x1010mol/m2sPa for PeO2 and up to 18.0 for S. These ranges are much larger than conventional plastics that exhibit PeO2 from 0.10x1010 to 0.20x1010mol/m2sPa and S up to 4.5. It was demonstrated from a food-requirements-driven (Tailorpack modelling) and a multiscale film structuring (WG-based composites) approaches, that transfer properties of WG-based films would fit the requirements of the six selected fruits and vegetables better than conventional plastics. Copyright (c) 2012 John Wiley & Sons, Ltd.

The properties and morphologies of blends of poly(butylene succinate) (PBS) and glycerol-plasticized thermoplastic starch (TPS) were investigated. Bis-pyrrolidone-type monomers (obtained from itaconic acid) with various sizes of alkylidene spacers were synthesized and polycondensed with various diamines. The resultant polycondensates were used as compatibilizers to improve interfacial adhesion in PBS/starch blends. The presence of long hydrophobic -CH2- sequences in the compatibilizers improved the elongation-at-break during tensile tests. The enhanced compatibilization induced by these copolymers is presumably because of the hydrophobic interaction with PBS and the hydrophilic hydrogen bonding with starch. The uncompatibilized TPS/PBS exhibited a dispersed morphology with blends of low- and high-starch content, whereas the compatibilized blends presented a co-continuous phase. Bis-pyrrolidone-type monomers (obtained from itaconic acid, which is a renewable chemical identified in the top 12 value-added chemicals from biomass) with alkylidene spacers of variable size were synthesized and polycondensed with various diamines. The resulting polycondensates were used as compatibilizers to improve interfacial adhesion in poly (butylene succinate) (PBS)/plasticized starch blends. The interfacial adhesion between PBS and plasticized starch was improved using these polycondensates.

Nanocomposite films were prepared by a thermo-mechanical process from wheat gluten (WG) and unmodified montmorillonite (MMT). The present work aims at predicting the relationships between the decrease in relative diffusivity of liquid water and the structure of the nanocomposite films, from in situ evaluation of the MMT size aspect ratio and volume fraction, and by using a simple tortuous path mathematical model. The modelling approach first allowed predicting and validating the tortuosity effect of MMT particles on liquid water transport properties of WG-based films. In spite of a well-exfoliated nanocomposite structure, the liquid water diffusivity in WG-based films can at best be decreased by a factor of 2 with this type of clay nanoparticle, which was in agreement with the Bharadwaj model predictions. This study underlines the necessity to achieve a totally exfoliated nanocomposite structure, and above all, to select layered silicates displaying higher size aspect ratio values in order to efficiently improve water barrier properties of WG-based nanocomposite films. Furthermore, the extremely complex structure of nanocomposite materials makes detailed morphological studies often difficult, time and cost consuming. (c) 2012 Elsevier Ltd. All rights reserved.

International audience; In this work, we aimed at studying formulation and design of powders by modified wet compression method. In order to focus only on the role of the liquid binder in the mechanical cohesion of compacts, glass beads were used as model particles because they do not deform or fragment at the compression pressure used (35kN). The three different binders studied were sugars: fructose, glucose and saccharose, used as solutions. Therefore, compacts were stored at controlled conditions until reaching water activity equilibrium at a fixed temperature of 25 degrees C. Then, the tensile strength of the compacts was determined using a Brazilian test. It was found to be dependent on the water activity. Critical values of Aw were measured (A(w) = 0.23 for the fructose, A(w) = 0.33 for the glucose, and A(w) = 0.44 for the saccharose), beyond which the glass transition phenomenon of the sugars appeared, and resulted in a sharp drop in the mechanical strength of the compacts. The classification of the sugars according to their respective glass transition temperature (Tg(fructose) < Tg(glucose), < Tg(saccharose)) permitted to confirm the role of the glass transition of the sugars as binders in the mechanical resistance of the compacts. Finally, sorption isotherms of the sugars coupled to the tensile strength results showed that the main parameter for predicting mechanical strength of the compact was the amount of sorbed water by the sugar, regardless to his nature.

[EN] The aim of this study is to analyze the mobility of polymer chains in semicrystalline poly(vinylidene fluoride) (PVDF). PVDF crystallizes from the melt in the crystalline phase. The transformation from the phase to the electroactive phase can be induced by stretching at temperatures in the range between 80 and 140 ◦C. The spherulitic structure of the crystalline phase is deformed during stretching to form fibrils oriented in the direction of the strain. The amorphous phase confined among the crystalline lamellae is distorted as well and some degree of orientation of the polymer chains is expected. Dynamicmechanical and dielectric spectroscopy measurements were performed in PVDF films stretched to strain ratios up to 5 at temperatures between 80 and 140 ◦C. Dynamic-mechanical measurements were conducted between −60 ◦C and melting and in this temperature range the relaxation spectra show the main relaxation of the amorphous phase (called -relaxation) and at higher temperatures a relaxation related to crystallites motions (c-relaxation). Although the mean relaxation times of the -relaxation are nearly equal in PVDF before and after crystal phase transformation, a significant change of shape of the relaxation spectrum proves the effect of chain distortion due to crystal reorganization. In stretched PVDF the elastic modulus of the polymer in the direction of deformation is significantly higher than in the transversal one, as expected by chain and crystals fibril orientation. The recovery of the deformation when the sample is heated is related with the appearance of the c-relaxation. Dielectric spectroscopy spectrum shows the main relaxation of the amorphous phase and a secondary process (-relaxation) at lower temperatures. Stretching produces significant changes in the relaxation processes, mainly in the strength and shape of the main relaxation. The Havriliak-Negami function has been applied to analyze the dielectric response., This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade-COMPETE" and by national funds by FCT-Fundacao para a Ciencia e Tecnologia, project references NANO/NMed-SD/0156/2007, PTDC/CTM/69316/2006 and PTDC/CTM-NAN/112574/2009. V. S. thanks the FCT for the SFRH/BPD/63148/2009 grant. JLGR acknowledges the support of the Spanish Ministry of Science and Innovation through MAT2010-21611-C03-01 (including the FEDER financial support), and EUI2008-00126 projects and funding in the Centro de Investigacion Principe Felipe in the field of Regenerative Medicine through the collaboration agreement from the Conselleria de Sanidad (Generalitat Valenciana), and the Instituto de Salud Carlos III (Ministry of Science and Innovation). The authors also acknowledge support from the COST Action MP1003, 2010 "European Scientific Network for Artificial Muscles".

International audience; The influence of kaolinite content within a plasticized starch matrix on the glass transition and decomposition temperatures, water uptake, transparency and UV-vis blocking is reported. Exfoliation of the kaolinite clay within the composite is enhanced when previously intercalated with DMSO. The DMSO-intercalated kaolinite brings in advantages for the clay dispersion within the polymer matrix, the transparency and the water uptake. The transparency of the films is better preserved when DMSO intercalated kaolinite is used and a clay load between 2% and 6%, leads to a significant reduction of the UV light transmission.

The agglomeration phenomenon of amorphous particulate material is a major problem in the food industry. Currently, the glass transition temperature (Tg) is used as a fundamental parameter to describe and control agglomeration. Models are available that describe the kinetics of the agglomeration process as a function of the distance of the material from Tg (i.e. T - Tg). In practice these models are often not applied because they assume that the powder material is instantly in equilibrium with the humidity conditions of the environment and that solid mobility only occurs at T > Tg. Insights in the kinetics and mechanisms of water transport in powder material can help to better understand and control powder agglomeration. For this purpose, gravimetric step-change water sorption experiments were performed on maltodextrins as a function of the water activity aw. The maltodextrins vary in dextrose equivalents (DE), particle size and morphology. The experimental results were compared with a Fickian diffusion model in order to understand the dependency of the transport mechanism on water concentration gradient and material relaxation. The water transport kinetics in the maltodextrins with low DE (i.e. 6) were well described by Fickian diffusion for low aw, independently of particle size and morphology, until relaxation phenomena started to occur at an aw corresponding to T - Tg = -20 °C. The importance of the matrix relaxation phenomena on the water transport mechanism increased with increasing DE (i.e. 29 and 32), not showing any relationship with the Tg. The results of this study indicate that the water migration mechanism is controlled by relaxation phenomena when the amorphous material is still far from the glass–rubber transition. The T - Tg at which the relaxation phenomena occur depends on the material. On the contrary, the T - Tg parameter could well describe the onset of agglomeration, independently from the material properties. Therefore, it can be concluded that within the conditions of this study, matrix relaxation occurring far below Tg did not affect the onset of agglomeration.

We describe the water activity of meat, being a mixture of proteins, salts and water, by the Free-Volume-Flory–Huggins (FVFH) theory augmented with the equation. Earlier, the FVFH theory is successfully applied to describe the thermodynamics to glucose homopolymers like starch, dextrans and maltodextrins. We have estimated parameter values from sorption isotherms of unsalted, lean meat products and model proteins like elastin and gelatin. These parameter values are quite similar to those found for glucose homopolymers. Moist meat products are also characterized with a water holding capacity, which we can describe with the Flory–Rehner theory. Subsequently, we have been able to predict very accurately the sorption isotherms of salted meat products and gelatin gels. Hence, the thermodynamics of foods can be described without the use of the controversial concept of bound/unfreezable water. Comparison of FVFH theory combined with Flory–Rehner theory to concentrated systems shows that the theory contains terms that are double counting for elastic effects – which makes us conclude that the validity of the Flory–Rehner theory is restricted to the (semi)-dilute regime. A complete thermodynamic description is proposed via mathematical matching of the FVFH and Flory–Rehner theory.

We give an overview of the many opportunities that arise from approaching food structuring from the perspective of soft matter physics. This branch of physics employs concepts that build upon the seminal work of van der Waals, such as free volume, the mean field, and effective temperatures. All these concepts aid scientists in understanding and controlling the thermodynamics and (slow) dynamics of structured foods. We discuss the use of these concepts in four topics, which will also be addressed in a forthcoming Faraday Discussion on food structuring.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; The effect of water activity on anthocyanin degradation and non-enzymatic browning (NEB) indices was determined in a blackberry juice system heated to high temperature. Blackberry juice samples mixed with quartz sand at three different water activities (a(w) of 0.34, 0.76 and 0.95) and having the same concentration of anthocyanins (51 +/- 4 mg 100g(-1) WB) were heated in a hermetically sealed reactor under non-isothermal conditions (100 to 140 degrees C). Reaction kinetics were well-represented by first-order reaction models. A non-isothermal method was used for the identification of kinetic parameters, and the confidence interval for each parameter was determined via Monte-Carlo simulations. The estimated parameters revealed an increase in the anthocyanin degradation reaction rate constant (k(ref)) from 0.9 to 3.5 x 10(-3) s(-1) as the water activity decreased from 0.99 to 0.34. The corresponding activation energies (Ea) for anthocyanins and NEB index were modified to a lesser extent by variations in water activity. Hence, the reduction of water activity had a negative effect on anthocyanin stability at high temperatures. (C) 2012 Elsevier Ltd. All rights reserved.