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The determination of intrinsic chain stiffness of conjugated polymers is challenging, in particular, for scattering techniques because of their strong light absorption and structural instability du...

The core-shell structure of nanoparticles (5 nm radius) of silica grafted with polymer growing from the particle ("grafting from") is characterized by small angle neutron scattering (SANS), to our knowledge for the first time. This is made possible by a good control of the colloidal dispersion at each step of the synthesis. With this aim, we have improved our chemical procedure based on atom transfer radical polymerization (ATRP), which allows a good control of kinetics and polydispersity: the reaction takes place in a polar solvent, and the reaction medium remains always crystal clear. For such small particles, in contrary to direct space imaging, SANS is appropriate for characterization of the polymer corona as well as of the silica core using contrast matching provided by mixing normal and deuterated solvent. This allows checking of the level of aggregation at the nanoscale, which is found to be limited to a few percent of the particles in the reaction batch. After an initial slight increase, it is reduced by further polymerization, while the polymer layer grows progressively. After purification, grafted silica can be characterized accurately: its scattering can be fitted by a model of a silica core containing three to five particles surrounded by a polymer shell of thickness 7 nm. This is in good agreement with chain length and grafting density (214 sites per particle) evaluated by chemical analysis; hence SANS provides quantitative insight on chemical synthesis.

Mixing negatively charged polyelectrolyte (PEL) with positively charged gold nanoparticles (Au NPs) in aqueous solution results in electrostatics complexes of different shapes and compactness. Here, when complexing with a semirigid PEL hyaluronic acid (HA), we obtain crystals made of nanoparticles in a new region of the phase diagram, as evidenced by small-angle X-ray scattering (SAXS). The Au NPs were initially well dispersed in solution; their size distribution is well controlled but does not need to be extremely narrow. The bacterial hyaluronic acid, polydispersed, is commercially available. Such rather simple materials and mixing preparation produce a highly ordered crystalline phase of electrostatic complexes. The details of the interactions between spherical nanoparticles and linear polymer chains remain to be investigated. In practice, it opens a completely new and unexpected method of complexation. It has high potential, in particular because one can take advantage of the versatility of Au NPs associated with the specificity of biopolymers, varied due to natural biodiversity.

Various studies have shown that food structure has an impact on digestion kinetics. We focus here on the effects of gastric and intestinal enzymes (in-vitro digestion) on two canola seed storage proteins, napin and cruciferin. To monitor structure effect we conducted experiments on gels of these proteins at different pHs, yielding different structures and elastic modulus. What is new is to get information on the mechanisms at the lowest scales, using imaging and radiation scattering at large facilities: Synchrotron fluorescence microscopy, X-Ray scattering, at SOLEIL synchrotron, and Small-Angle Neutron Scattering, at Laboratoire Leon Brillouin reactor. We can identify the mechanisms at each step and in two distinct scale ranges, observed simultaneously, the one of the individual protein scale and the one of the structure connectivity: • during gelation individual canola proteins are not deeply modified in comparison with their state in solution ; larger scale gel heterogeneity appears due to connectivity or aggregation • in the gastric step (up to 40 min): ○ at short scale (large q) we see that the proteins disintegration is much slowed down in gels than in solutions, particularly in the gastric phase; ○ at larger scales (low q), we see that the gel structure is also self-resistant to the action of the enzyme (pepsin). • in the intestinal step, such kinetics differences hold until major disintegration after no more than 15 min.

International audience; Quantitative ultrasound (US) techniques have an attractive potential for the non-invasive and real-time characterization of the structural and mechanical properties of food. The objective of the present study is to unravel the determinants of the variations of US properties during sol-gel transition of emulsion filled gels of agar and gelatin, due to the relative contributions (i) of their individual components and (ii) of their combined interactions. Nine model foods were designed, accounting gradually for the complexity of an emulsion filled gel composed of water, sucrose, agar, gelatin and sunflower oil. A quantitative US device was designed to monitor the sol-gel transition of the model foods. US velocity, reflectivity and attenuation were measured at 50 °C (sol-state) and 20 °C (gel-state) with a 1 MHz transducer in pulse-echo mode. US data were then compared to visco-elastic shear moduli and density measurements. Bulk elastic modulus was shown to prevail over density for explaining the variations of US velocity and reflectivity during sol-gel transition, while high gelatin concentration and interactions between agar and gelatin had an impact on US attenuation. In addition to the fact demonstrated here that US reflectivity is easier to measure compared to velocity and attenuation, the literature reports that this parameter also highly depends on the mechanical coupling of interfaces. Therefore, this study is a baseline for future investigations on the potential of US reflectivity for the characterization of physical interactions between food and more complex surfaces, so that to mimic tongue-food interaction during oral processing.

International audience; The chain conformation in sulfonated polystyrene PSSNa of a degree of sulfonation 0.34

We study for the first time the structure of stable finite size clusters (i.e., colloidal molecules) obtained by self-assembly of cationic gold nanoparticles (i.e., atoms) mediated by a flexible polyanion. We reveal with nondenaturizing techniques a striking structural transition from 1D small chains of 12 gold nanoparticles (AuNPs) with a self-avoiding conformation to 3D fractal clusters of 130 AuNPs with short-range ordering around the charge inversion threshold. Interestingly, these well-defined structures are obtained by simple mixing in water without anisotropic functionalization or external forces. As a preliminary step, we introduce a new synthesis pathway leading to well-defined cationic AuNPs of controllable size that can be dispersed in H2O or D2O without aggregation and ligands' self-assemblies. On this occasion, we point for the first time that usual procedures do not enable to eliminate cationic ligands' self-assemblies that could play an undesired role in AuNPs' self-assembly through electrostatic interactions.

International audience; Foams are multiscale materials that have an enormous number of uses. As the relevant structural length-scales span from a few nanometres up to millimetres a number of characterisation methods need to be combined to obtain the full material structure. In this review we explain how foams can be explored using Small Angle Neutron Scattering (SANS). We remind the reader of the basics of SANS and contrast variation before we describe the different types of experiments that have been carried out on foams emphasising the specific role of neutrons in learning about the systems. To date SANS has been used to measure different foam structural parameters, such as the film thickness and the bubble size. Several studies have also been carried out to elucidate the organisation of the stabilising objects in the bulk solution. Finally we show how SANS measurements can be used to measure foam composition. Some of the accessible information is unique to SANS experiments, but as the method is still not very widely used on foams the review is also aimed to act as an introduction on how to carry out such measurements on foams.

We present an investigation of the swelling dynamics of end-grafted hydrogenated polystyrene (h-PS) chains confined between a solid substrate and a deuterated polystyrene (d-PS) melt, based on neutron reflectometry experiments. The segment density profile of the grafted chains was measured for different annealing times. The kinetics of relaxation was quantified by measuring the amount of melt chains that have crossed the initial h-PS/d-PS sharp interface as a function of the annealing time. The dependence of this kinetics versus the molecular weight of the grafted chains, the melt chains, and the grafting density is investigated and compared to a proposed scaling model inspired from the previous work of Milner, McLeish, and O’Connor.1,2 Moreover, the relaxation kinetics is found to highly depend on the polydispersity of the polymer brushes, and we propose a way for taking that parameter into account.

International audience; PACS 62.23.St Complex nanostructures, including patterned or assembled PACS 82.35.Rs Polyelectrolytes PACS 83.85.Hf X-ray and neutron scattering Abstract. Aggregation of nanoparticles of given size R induced by addition of a polymer strongly depends on its degree of rigidity. This is shown here on a large variety of silica nanoparticle self-assemblies obtained by electrostatic complexation with carefully selected oppositely charged bio-polyelectrolytes of different rigidity. The effective rigidity is quantified by the total persistence length L T representing the sum of the intrinsic (L p) and electrostatic (L e) polyelectrolyte persistence length, which depends on the screening, i.e., on ionic strength due to counterions and external salt concentrations. We experimentally show for the first time that the ratio L T /R is the main tuning parameter that controls the fractal dimension D f of the nanoparticles self-assemblies, which is determined using small-angle neutron scattering: (i) For L T /R1, L e is strongly increased due to the absence of salt and repulsions between nanoparticles cannot be compensated by the polyelectrolyte wrapping, which allow a spacing between nanoparticles and the formation of one dimensional pearl necklace complexes. (iv) Finally, electrostatic 2 screening, i.e. ionic strength, turned out to be a reliable way of controlling D f and the phase diagram behavior. It finely tunes the short-range interparticle potential, resulting in larger fractal dimensions at higher ionic strength.

International audience; Neutron reflectivity has been used to investigate the effect of shear on the conformation of hydrogenated polystyrene chains end-grafted on a silicon wafer and covered by a deuterated polystyrene melt, in the grafting regime where the grafted chains at equilibrium extend in the bulk up to their radius of gyration. An experimental setup has been built to shear the samples above their glass transition temperature and then quench them rapidly after the shear. The flow-induced distorted conformation of the end-tethered chains was characterized by neutron reflectivity. We show that the effect of the shear is a decoupling between the grafted chains and the bulk chains which leads to a strong slip of the polymer melt at the solid interface.

International audience; We aim at combining high coercivity magnetic nanowires in a polymer matrix in a view to fabricate rare-­‐earth free bonded magnets. In particular, our aim is to fabricate anisotropic materials by aligning the wires in the polymer matrix. We have explored the different parameters of the fabrication process in order to produce a material with the best possible magnetic properties. We show that the choice of a proper solvent allows obtaining stable nanowire suspensions. The length and the type of the polymer chains play also an important role. Smaller chains (M w

The question of the influence of nanoparticles (NPs) on chain dimensions in polymer nanocomposites (PNCs) has been treated mainly through the fundamental way using theoretical or simulation tools and experiments on well-defined model PNCs. Here we present the first experimental study on the influence of NPs on the polymer chain conformation for PNCs designed to be as close as possible to industrial systems employed in the tire industry. PNCs are silica nanoparticles dispersed in a styrene-butadiene-rubber (SBR) matrix whose NP dispersion can be managed by NP loading with interfacial coatings or coupling additives usually employed in the manufacturing mixing process. We associated specific chain (d) labeling, and the so-called zero average contrast (ZAC) method, with SANS, in situ SANS and SAXS/TEM experiments to extract the polymer chain scattering signal at rest for non-cross linked and under stretching for cross-linked PNCs. NP loading, individual clusters or connected networks, as well as the influence of the type, the quantity of interfacial agent and the influence of the elongation rate have been evaluated on the chain conformation and on its related deformation. We clearly distinguish the situations where the silica is perfectly matched from those with unperfected matching by direct comparison of SANS and SAXS structure factors. Whatever the silica matching situation, the additive type and quantity and the filler content, there is no significant change in the polymer dimension for NP loading up to 15% v/v within a range of 5%. One can see an extra scattering contribution at low Q, as often encountered, enhanced for non-perfect silica matching but also visible for perfect filler matching. This contribution can be qualitatively attributed to specific h or d chain adsorption on the NP surface inside the NP cluster that modifies the average scattering neutron contrast of the silica cluster. Under elongation, NPs act as additional cross-linking junctions preventing chain relaxation and giving a deformation of the chain with the NP closer to a theoretical phantom network prediction than a pure matrix.

We report on the influence of parameters controlling filler dispersion and mechanical reinforcement in model nanocomposites. We elaborate a series of nanocomposites and present a structural characterization of silica dispersion in polymer matrix for several particle sizes and polymer matrices, at all relevant scales, by coupling Small Angle X-ray Scattering and Transmission Electronic Microscopy. The mechanical properties are investigated in the linear regime by coupling Dynamical Mechanical Analysis and plate/plate rheology. The results show that: (i) for all filler sizes and matrices, a structural transition is observed from non-connected fractal aggregates at low silica concentration to connected network at high particle content. (ii) In the dilute regime, the reinforcement implies a polymer chain contribution with different possible origins: increase of entanglements density for PS and increase of friction coefficient for PMMA. (iii) In the concentrated regime, for a given polymer, the reinforcement amplitude can be tuned by the rigidity of the filler network, which directly depends on the particle–particle interaction.

The advantage of small angle neutron scattering associated with isotopic labelling through deuteration is illustrated in the case of mixed systems, created by associating already well-known systems of characteristic structures; this is also important for applications. Our first mixed system associates charged polymer chains, polyelectrolytes (here polystyrene sulfonate, PSS), with oppositely charged particles, proteins (here lysozyme). Different fractions of deuterated water (D 2 O) mixed with normal water are used to match the scattering length density of the protein or of the polymer in non-deuterated or deuterated version. First, this allows us to separate the protein and the polymer signal: we can then distinguish a case where the structures of each species alone in water are hardly modified by mixing, except for interconnections yielding a gel , and a case inducing complete change into a structure common to both species, made of aggregated globules . Second, using, for counterions of the polyions, deuterated TetraMethylAmmonium, together with matching both protein and polymer, we establish unambiguously the counterion release into the solvent. Third, matching only a fraction of polymer chains, the other being deuterated, we extrapolate at zero deuterated fraction their form factor and describe the chain conformation inside the complexes. Fourth, we illustrate the possibilities of modelling the signal on a second example of mixed system: a nanocomposite made of silica particles surrounded by polymer dispersed into a deuterated polymer matrix. Chains are then visible in such reinforced polymer system, in particular when it is submitted to elongation: we discuss a possible model for an ideal system, introducing the scattering contribution from deformed chains, another subject studied at LLB. To cite this article: F. Boue et al., C. R. Physique 8 (2007).

International audience; Nano-hybrid hydrogels were prepared by cross-linking polymerization of N,N-dimethylacrylamide (DMA) within a dispersion of silica nano-particles. Working at constant polymer/water ratio, the mechanical properties of hydrogels can be finely tuned by changing either the level of covalent cross-linker and/or the amount of particles that act as physical cross-linkers through specific adsorption of PDMA chains. Whatever is the cross-linking ratio (from 0 to 1 mol%), the introduction of silica nano-particles dramatically improves the mechanical behavior of hydrogels with a concomitant increase of stiffness and nominal strain at failure. The physical interactions being reversible in nature, the dynamics of the adsorption/desorption process of PDMA chains directly controls the time-dependence of the mechanical properties. Small angle neutron scattering experiments, performed in contrast matching conditions, show that silica particles, which repel themselves at short range, remain randomly dispersed during the formation of the PDMA network. Although PDMA chains readily interact with silica particles, no significant variation of the polymer concentration was observed in the vicinity of silica surfaces. Together with the time dependence of physical interactions pointed out by mechanical analyses, this result is attributed to the moderate adsorption energy of PDMA chains with silica surfaces at pH 9. From 2D SANS experiments, it was shown that strain rapidly gives rise to a non affine deformation of the hybrid network with shearing due to the transverse compression of the particles. After loading at intermediate deformation, the particles recover their initial distribution due to the covalent network that is not damaged in these conditions. That is no longer true at high deformation where residual anisotropy is observed.

We report the formation of well-defined and uniformly sized nano- and microparticles in aqueous solutions of oppositely charged polyelectrolytes and surfactants. Such mixed aqueous solutions are currently the focus of much attention because of the large number of applications in which they are involved. [1,2] The particles that we have obtained are spherical and possess an internal liquid-crystal-like structure. The radius of the particles is independent of the polymer concentration but increases exponentially with the surfactant concentration. The particle size can therefore be varied over a broad range, from 10 nm up to several micrometers. Here, we discuss the conditions used to synthesize these particles. Upon mixing the polyelectrolytes and surfactants, two distinct behaviors are observed. First, precipitation occurs above a critical concentration for both the polymer and the surfactant when the two species are oppositely charged (Fig. 1). In contrast to the usual precipitation of salts, or even mixtures of two surfactants, this precipitation does not occur at a point where the ionic concentrations of the two species are close. In the following discussion we denote the surfactant and polymer ion concentrations by Cs and Cp, respectively. The phase separation has an “associative” character: at large Cp, the surfactant concentration threshold Cs* is roughly independent of

Polymer chains are grafted from silica nanobeads. The method consists in grafting first the initiator molecules on the silica surface. Then, the polymerization of styrene or n-butyl methacrylate using Atom Transfer Radical Polymerization, is conducted. The nanoparticles are kept in solution during the whole process to avoid irreversible aggregation. The state of dispersion of the grafted silica nanoparticles is followed by Small Angle Neutron Scattering, as well as the quantity and the spatial organisation of the polymer. This is done during the functionalisation and the polymerization, but also after purification where free polymer chains are eliminated. This permits to reach a quantitative level of SANS analysis from these purified particles, which is compared to chemical data given by Size Exclusion Chromatography and Thermogravimetric analysis.

Polymer chains were grafted from silica beads (colloidal sol in dimethylacetamide) by atom transfer radical polymerization (ATRP), via the ‘grafting from’ method. The grafting of the initiator onto the silica surface was done in two steps. First, thiol-functionalization of the surface was achieved via silanization with a mercaptopropyl triethoxysilane. Second, we performed an over-grafting of the surface by reacting the thiol with 2-bromoisobutyryl bromide to generate the halogen-functional ATRP initiator. The nanoparticles were kept in solution (in the same solvent) at each stage of the functionalization (even during the purification steps), as this is the only way to avoid irreversible aggregation. Then, the polymerization of styrene was conducted. Control of both the molecular weight and the density of grafted chains can be achieved by this method. Careful characterization such as gel permeation chromatography, 29 Si CP/MAS NMR, elemental analysis, infrared spectroscopy and thermo-gravimetric analysis is performed. The state of dispersion of the grafted nanoparticles is followed in details by small angle neutron scattering and results obtained from this technique are presented here as well as the way the SANS data can be treated. Connection is systematically done between the information provided by this technique and the improvement of the synthetic procedure.

Polymer chains are grafted from silica beads (colloidal sol in dimethylacetamide) by atom transfer radical polymerization (ATRP). The method consists of grafting first the initiator molecules on the silica surface (“grafting from” method), in two steps. First, thiol-functionalization of the surface was achieved via silanization with a mercaptopropyl triethoxysilane. Second, we performed an overgrafting of the surface by reacting the thiol with 2-bromoisobutyryl bromide to generate the halogen-functional ATRP initiator. From that, the polymerization of styrene was conducted. Control of both the molecular weight and the density of grafted chains can be achieved by this method. The other originality of this work is that we keep the nanoparticles in solution at each stage of the procedure (even during the purification steps), as this is the only way to avoid irreversible aggregation. The state of dispersion of the grafted nanoparticles is followed by small-angle neutron scattering. Characterizations such as g...

We report on small-angle neutron scattering measurements obtained in situ on three-dimensional aqueous foams stabilized by sodium dodecyl sulfate. Isotropic as well as anisotropic scattering data have been collected for two kinds of foams: wet foams in the steady-state regime of constant gas bubbling and dry foams under free draining conditions. Reliable scattering spectra were obtained within a few minutes, even for very dry foams. All spectra have a basic I(q) ∼ q-4 behavior on which a foam specific structure is superposed. The q-4 decrease at low q can be interpreted in terms of a Porod law from which the average bubble size is determined for both wet and dry foams. For wet foams, the intensity is modulated at high q by the structural organization of the surfactants in the liquid fraction of the foam (micelles). Remarkably, for dry foams only, the structure also appears at intermediate q, corresponding to the film thickness. This structure can be enhanced by using deuterated sodium dodecyl sulfate to ...

The soft matter group of LLB is centered on Small Angle Neutron Scattering (SANS). It is in charge of three classical SANS facilities (one annular detector and two XY detectors) and one polarized neutron SANS, and is developing a new USANS diffractometer. The group is also connected withneutron reflectivity, and to a lesser extent to inelastic scattering (spin echo, time of flight). In the field of soft matter, the expertise has been for many years focused on polymer solutions (neutral and charged), adsorbed polymers, polymer melts, and liquid crystalline polymers, witha focus on the effect of mechanical deformation (“rheo-SANS”). More recently, such deformation effects have been studied also on polymer latex films and latex-silica composites. We have chosento present this work here, which is at the boundary between polymer and colloid science, since interactions between silica particles in the films are involved and control partly the reinforcement of the polymer film. We will balance this examp...

Aqueous solutions of a well-defined poly(N-isopropylacrylamide-co-sodium 2-acrylamido-methylpropanesulfonate) (NIPAM/NaAMPS in a 95/5 molar ratio) have been investigated by means of small-angle neutron scattering (SANS) and rheological experiments as a function of temperature ( 25°C\(\)T\(\) 60°C) and polymer concentration ( 0.5wt% \(\)C\(\) 12wt%). The solutions remain optically transparent and isotropic over the whole temperature range, in contrast with the homopolyNIPAM which precipitates above its lower critical solution temperature (LCST = 32°C). Upon addition of salt, the systems undergo a micro-macrophase separation. At temperatures above 45°C, the SANS spectra exhibit a sharp peak at a scattering wave vector, qmax, which increases slightly with temperature. At high temperature ( T∼ 60°C), the scattered intensity follows a power law I(q) ∼q-4 in the asymptotic regime, characteristic of two-density media with sharp interfaces, and qmax is found to vary with polymer concentration as qmax∼C0.22. Estimates of the typical sizes give values between 40 A and 200 A. These results provide a strong evidence of a thermally induced microphase separation, which is corroborated by the very sharp increases of the viscosity (over 2 decades) and of the stress relaxation time of the solutions, occurring in the temperature range where the scattering peak is observed. The results are discussed and compared with the theoretical models proposed for weakly charged polyelectrolytes in a poor solvent.

Quantitative Ultrasound techniques are good candidates for the in situ and real-time mechanical characterization of tongue-food-palate system, and thus to improve the understanding of the determinants of texture perception of food. Different model foods (consisting in gels and emulsion filled gels composed of agar and/or gelatin) have been designed for their contrasting properties in terms of texture perceptions. Prior to the feasibility study of a Quantitative Ultrasound method to monitor their mechanical breakdown during a compression, the aim of this study is to determine the respective roles of structure and mechanical properties of the different model foods in the variations of ultrasonic wave properties. Ultrasonic velocity, reflectivity, and attenuation were monitored during the sol-gel transition (from 50°C to 20°C) at 1 MHz in pulse-echo mode, and were confronted to visco-elastic moduli and mass density measurements. The results put in evidence the role of biopolymer concentration (independently ...

The development of non-invasive methods is critical for a better understanding of the biomechanical phenomena involved in the dynamic mechanisms of food texture perception during oral processing. The aim of the present study is to investigate in vitro the potential of a quantitative ultrasound device in order to monitor the mechanical properties of tongue-food interface during a compression. A tongue-palate bio-mimicking set-up was designed, consisting in a traction-compression machine equipped with tongue and palate phantoms. Gels and emulsion filled gels were considered as model foods for their wide ranges of texture properties. Finally, a 1 MHz ultrasonic transducer positioned under the tongue records in real-time the pulse-echo response of the tongue-food-palate system during a compression. The results put in evidence in vitro the potential of tongue-food interface reflexion coefficient to monitor the competitive and collaborative contributions (i) of the tongue-palate system (roughness, lubrication, ...

cited By 9; International audience; The structural evolution of nanoparticles (NPs) dispersion under uniaxial stretching and extension/retraction deformation cycles above Tg was investigated in model silica/polymethylmethacrylate (PMMA) nanocomposites (PNCs) by a combination of Small Angle X-ray Scattering (SAXS) and Transmission Electronic Microscopy (TEM). The different structure displacements and reorganizations can be quantitatively characterized as a function of elongation ratio, silica volume fraction and NP size. At low NP volume fraction, a rotation/orientation of non-connected aggregates is observed along the stretching direction, while the reinforcement is low and might be limited by the large-scale aggregates. At high volume fraction, the stress-strain curves exhibit three regimes. (i) At low stretching ratio, in the linear deformation regime, reinforcement is driven by the primary network filler structure. (ii) Above a few percent of deformation, a yield is observed and can be associated to the network breakdown as revealed by cyclic extension/retraction experiments. (iii) As a result of this yield, at larger deformation, the stress curve appears as shifted upward with respect to the one of pure polymer. A persistence of this vertical shift (constant value up to large deformation) might be related with SAXS measurements to a non-affine deformation of the NPs network due to new structural arrangements, while in a second case, the decrease of stress to the pure polymer value with increasing deformation is related with observation of affine deformation after the yield. Finally, affinity and non-affinity after yielding are discussed for all the systems according to the strength of the NP-NP interaction. © 2014 Elsevier Ltd. All rights reserved.

We have used helium-3 nuclear reaction analysis to measure the interdiffusion of linear polystyrene into a film of crosslinked polystyrene and the intradiffusion of polystyrene in polystyrene networks. The interdiffusion is compared with that predicted from the Kramer-Sillescu theory, and is found to be considerably faster. This is attributed to the relaxation of inhomogeneities in the network. The molecular weight and crosslinking dependence of the intradiffusion coefficients of free polystyrene chains trapped inside networks is discussed in terms of the simple tube model and provides reasonably good agreement with that predicted from reptation theory.

We have used neutron reflectometry and carbon and neon forward recoil spectrometry to measure the surface segregation of deuterated polystyrene from a hydrogenous polystyrene network. We find that when the linear polymer is of a high molecular weight (~600 000), the surface segregated profile can be predicted by mean field theory. In these systems the segregation is a rather slow function of time, reflecting the large number of entanglements in such crosslinked mixtures. When the deuterated polystyrene is of a lower molecular weight (~100 000), the surface segregated layer does not evolve monotonically with time but the shape of the profile can be predicted by mean-field theory. However, when the network is significantly crosslinked, the linear polymer is expelled from the network.

We report preliminary simulations of anisotropic scattering from aggregates of small hard spherical particles embedded in an elastic polymer matrix, using simple geometrical methods. First we build several types of aggregates in three dimensions: crystalline, amorphous compact, fractals, of different numbers of particles and varying polydispersity. We then turn to the spectra of deformed samples simulated in two dimensions. We impose an affine displacement inside the matrix to the fillers, which can be isolated particles or small aggregates, and account for the collisions which arise due to lateral shrinking of the material. The two-dimensional scattering spectra are shown and discussed. They reproduce experimentally observed isointensity curves: ellipses, banana-shaped maxima and splitting of these maxima in four spots. Finally, we explore the consequences of the reduction to two dimensions via statistics of the number of collisions. It is found that even if collisions are more important in 3 dimensions, the behavior is qualitatively similar in two and three dimensions.

This article reports a study of the chain conformation in thin films of amorphous polymer prepared by spin coating. Polystyrene chains of two molecular weights Mw, 230 000 and 660 000, are confined in layers of thickness equal to either 1000 A, thus greater than their unperturbed radii of gyration Rg, or 100 A, thus smaller than Rg. The form factor of the chain inside the layer is measured by small-angle neutron scattering. Changes of the scattering are observed as a function of the film thickness in the intermediate scattering vector range. We analyze the data in the frame of the wormlike model. In the 1000 A films, the chain has the same Gaussian conformation as in the bulk. In the films of 100 A, the persistence length of the chain is increased (compared to 9.2 A the value in the bulk) up to 45 A, for both Mw values. However, the corresponding scattering intensity is higher than expected for such an extended chain.

We present the results of a neutron reflectometry study of the kinetics of penetration of a grafted polymer layer into a permanently cross-linked, chemically identical network. The polymer used was polystyrene. Initially the grafted chains are completely excluded from the network, and the interface between them is sharp. The segment density profile was measured after a series of annealing times to follow the kinetics of penetration. The range of annealing times was extended over 9 orders of magnitude by using time−temperature superposition. We observe a slow approach to equilibrium, in good agreement with theory, which predicts this to be logarithmic in time. The kinetics of penetration is slower for more densely cross-linked networks and for greater brush grafting densities. We also note a grafting density dependence of the equilibrium profile but, somewhat unexpectedly, no dependence on the density of cross-links.

Nanocomposites have been made by mixing soft particles (polymer latex) with hard particles (silica) in aqueous dispersions and extracting water to produce a dense film. Segregation between the two kinds of particles can be controlled, and even suppressed. The elongational modulus is strongly increased by such fillers at low deformations, and remains important at large deformations, which the samples can stand without breaking. Since the silica particles are small (200 A), we can follow their relative displacements under stretching, by Small-Angle Neutron Scattering, through analysis and simulation of the anisotropic patterns. The latter show a crossover from affine displacements to a set of shear displacements that let the particles avoid each other at large deformations. The shear could release the localized stresses (due to polymer confinement) and dissipate more energy. In this way it may contribute to the toughness of the composite against crack propagation.

It is suggested that the non-locality of the entropy part of the interaction parameter in partially miscible blends can be measured directly by scattering experiments. The structure factor computed in the random phase approximation is compared with experiments on weakly crosslinked polystyrene (PS) polyvinylmethylether (PVME) blends. These polymers have significantly different monomer units to form ‘smooth’ (PVME) and ‘rough’ (PS) polymers. An excess scattering is observed and related to the non-locality. It is further shown that these effects are significant near the glass transition of the blend. In particular, the influence of the non-local mixing entropy on the single chain behaviour close to the onset of the microphase separation is studied quantitatively.

International audience; The electrostatic complexation between model negatively charged silica nanoparticles (NPs) with radius R~10 nm and chitosan, a natural polyelectrolyte bearing positive charges with a semi-rigid backbone of persistence length of Lp~9 nm, was studied by a combination of SANS, SAXS, light scattering, and cryo-TEM. In this system, corresponding to Lp/R~1, we observe the formation of (i) randomly branched complexes in the presence of an excess of chitosan chains and (ii) well-defined single-strand nanorods in 10 the presence of an excess of nanoparticles. We also observe no formation of nanorods for NPs with poly-L-lysine, a flexible polyelectrolyte, corresponding to Lp/R~0.1, suggesting a key role played by this ratio Lp/R. In the intermediate range of nanoparticles concentrations, we observe an associative phase separation (complex coacervation) leading to more compact complexes in both supernatant and coacervate phases. This method might open the door to a greater degree of control of nanoparticles self-15 assembly into larger nanostructures, through molecular structural parameters like Lp/R, combined with polyelectrolytes/nanoparticles ratio.

We studied polydimethylsiloxane networks prepared by end-linking in the bulk. Neutron scattering and scanning light-scattering experiments indicate that the networks swollen with a “good solvent” exhibit rather strong spatial fluctuations of polymer concentration, which are nearly frozen-in. We attribute this effect to the presence of “defects” in the network structure, which is consistent with the results of high frequency rheology measurements, performed on dry networks. The spectrum of static fluctuations appears to be more sensitive to a change in the length of the precusor chains than to the proportion of dangling chains. We propose to explain this result by describing some of the network non-uniformities as fluctuations in the size of the shortest closed circuits along the network.

Polymer concentration fluctuations in poly(acrylic acid) gels subjected to uniaxial elongation are studied using small-angle neutron scattering (SANS). Different elongation ratios and neutralization degrees are considered. For non-ionized samples and for samples with added salt, the scattering intensity at small angles presents iso-intensity curves in the form of "butterflies", the absolute intensity in parallel direction being stronger than that in the perpendicular one. When the gel is sufficiently ionized, the "butterfly" patterns disappear and the intensity scattered in perpendicular direction is stronger than that in the parallel one, for the whole scattering wave vector range studied.

Measurements of the local orientational order and average chain anisotropy in non-uniform polystyrene are reported. Fourier-transform infrared dichroism spectroscopy has been used to determine the effects of short deuterated chains (Mw = 500 to 188 000) on the orientational relaxation of long entangled chains (Mw = 2 000 000) in bidisperse melts uniaxially deformed above the glass transition temperature. While the long-chain relaxation is found to be dependent on the short-chain concentration, the local orientational order of the latter is molecular weight dependent consistent with the classical relaxation theories. The FTIR experiments are also combined with small-angle neutron scattering measurements which probe the deuterated-chain anisotropy in the defomed melts. There is evidence, from the combination of the two techniques, that although the short chains possess a negligible local orientational order, there exists an important anisotopy in the short chain distribution in space.

The anisotropic small-angle neutron scattering from two different materials is considered. One is a polymer network permeated by free, uncross-linked, deuteriated chains. These free chains behave as mobile species. The other is made up of two networks, one being deuteriated, grown interwoven with each other. They are made of two different polymers which are immiscible, one being in a soft, rubbery state, the other in a hard, glassy state.The scattering of the two systems displays an unusual dependence upon the direction with respect to the stretching axis. The scattered intensity recorded along any direction which corresponds to an increase in the dimensions increases strongly with the elongation ratio. The isointensity patterns, so-called butterflies, have the shape of 8s, oriented along the stretching axis.We propose a general explanation: in both cases this increase is due to the separation between some hard, weakly deformed regions inside a softer matrix.This implies, for the network permeated by free chains, that a scattering contrast is created between hard and soft regions: the free chains migrate into the soft regions. The increase of the correlation length, ξ, along any extended direction of the sample (such as the one parallel to the stretching) reveals an intermediate regime at lower and lower values of the scattering vector, q. In this q range, the intensity, I(q), is superimposed on a limit curve, characteristic of each sample. The perpendicular scattering is essentially unaffected. Different continuous-medium elasticity theories have tried to explain such an anisotropy of the spatial fluctuations of concentration. Rather accurate measurements allow us to detect disagreements between these theories and experiment. In our opinion, this confirms our more direct picture: the progressive unscreening of the structure of the spatial distribution of the modulus.

International audience; In this paper we report the influence of biopolymer folding on nanoparticle spatial distribution in two typical bio-nanocomposite hydrogels. These systems consist of negatively charged nanosized fillers (polyoxotungstate clusters and silica particles, 2.2 nm and 23.0 nm in diameter, respectively) dispersed at low volume fractions in a positively charged gelatin hydrogel. The filler state of dispersion is investigated during triple helix folding by combining small-angle neutron scattering (SANS) and polarimetry experiments. Neutron contrast matching/polarimetry correlations indicate that the nanoparticle spatial distribution is clearly modified during triple helix folding for the two systems. In the first case, polyoxotungstate clusters are initially arranged in small finite size aggregates that grow with increasing triple helix rate: ΔRG ≈ +150% and ΔI(q → 0) ≈ +250% for Δ[helix] ≈ +40%. In the second case, silica particles initially form a connected network that undergoes a significant densification through gelatin conformational transition. In the two cases, the kinetics of triple helix folding is only slightly affected by the presence of the nanoparticles and their state of dispersion. In our experimental conditions, these two processes are almost thermo-reversible following triple helix unfolding.

International audience; We show by combining small-angle X-ray scattering (SAXS) and cryo-transmission electron microscopy (cryo-TEM) that anionic silica nanoparticles (SiNPs) assemble into well-defined 1D cluster when mixed with a dilute solution of semiflexible chitosan polycation. The nanorods are stable in excess of SiNPs and composed of 10 SiNPs well-ordered into straight single strands with length Lrod ≈ 184.0 nm and radius Rrod = 9.2 nm = RSiNPs. We point out that the ratio between the chitosan persistence length and the SiNP radius, which is here equal to 1, can be the determining condition to obtain such original objects.

International audience; The use of agricultural resources for industrial purposes will undoubtedly be one of the major challenges of the 21st century, either from the energetic point of view by the progressive replacement of fossil fuels or with respect to non-energy uses by making available new organic “biosynthons” to the chemicals industry. In such a context, we demonstrate here the strong potential of dispersions of saturated fatty acids and their hydroxylated derivatives, extracted from biological compounds of plant origin, as a new class of green surfactants.

SANS was used to study the effects of cross-link density on the structure of in situ sequential interpenetrating polymer networks (IPNs). The system investigated is a PSD (deuterated polystyrene-co-divinylbenzene) network built within a matrix network of PUR (polyurethane). The scattering can be approximated by the Debye-Bueche law with a q -4 dependence at intermediate values of have vector q, with departures from it at both low and very large values of q. At low q, this Debye-Bueche law yields a value of the structure factor S(q→0) and a correlation length ξ. At large q, it yields a value of the specific area S/VS being the total area and V the total volume

Small-angle neutron scattering (SANS) has been used to study the gelation of amylose solutions in water in the range of concentrations of 2 to 8% by weight. The results clearly indicate a phase separation between polymer-rich and water-rich regions and an organization into a self-similar structure, with a characteristic fractal dimension of 2.6, independent of polymer concentration. The size and composition of polymer-rich aggregating units also show little dependence on the polymer concentration. A study of the gelation process leads to the conclusion that the fine structure of the gels, probed in this experiment, is independent of the cooling rate.

The ethanolamine salt of 12-hydroxy stearic acid is known to form tubes having a temperature tunable diameter. Here, we study the behavior of those tubes at the air/water interface by using Neutron Reflectivity. We observed that tubes indeed adsorbed at this interface below a fatty acid monolayer and exhibit the same temperature behavior as in bulk. There is however a peculiar behavior at around 50 °C for which the increase of the diameter of the tubes at the interface yields an unfolding of those tubes into a multilamellar layer. Upon further heating, the tubes re-fold and their diameter re-decreases after which they melt into micelles as observed in the bulk. All structural transitions at the interface are nevertheless reversible. This provides to the system a high interest for its interfacial properties because the structure at the air/water interface can be tuned easily by the temperature.

This paper presents a study of the polymer-filler interfacial effects on filler dispersion and mechanical reinforcement in Polystyrene (PS) / silica nanocomposites by direct comparison of two model systems: un-grafted and PS-grafted silica dispersed in PS matrix. The structure of nanoparticles has been investigated by combining Small Angle Neutron Scattering (SANS) measurements and Transmission Electronic Microscopic (TEM) images. The mechanical properties were studied over a wide range of deformation by plate/plate rheology and uni-axial stretching. At low silica volume fraction, the particles arrange, for both systems, in small finite size non-connected aggregates and the materials exhibit a solid-like behavior independent of the local polymer/fillers interactions suggesting that reinforcement is dominated by additional long range effects. At high silica volume fraction, a continuous connected network is created leading to a fast increase of reinforcement whose amplitude is then directly dependent on the strength of the local particle/particle interactions and lower with grafting likely due to deformation of grafted polymer., Journal Polymer Science (2011)

International audience; We synthesized well-defined polystyrene-grafted silica nanoparticles by adapting our previous synthesis process without using free initiator. We were able to obtain a more versatile system in which we can tune the masses of the grafted chains while controlling the polymerization, the colloidal stability and avoid the formation of free polymer chains. The final grafted objects were characterized in a refined way using SANS and the contrast matching method.

6 pages; International audience; Ultrastable foams with an optimal foamability have been obtained using hydroxyl fatty acids tubes. The stabilization results from the adsorption of monomers at the air-water interface preventing coalescence and coarsening and from the presence of tubes in the Plateau borders limiting the drainage. Upon heating, tubes transit to micelles, which induces foam destabilization. Such foams are thus the first to have a temperature tunable stability.

International audience; We investigate the dispersion mechanisms of nanocomposites made of well-defined polymer (polystyrene, PS) grafted-nanoparticles (silica) mixed with free chains of the same polymer using a combination of scattering (SAXS/USAXS) and imaging (TEM) techniques. We show that the relevant parameter of the dispersion, the grafted/free chains mass ratio R tuned with specific synthesis process, enables to manage the arrangement of the grafted nanoparticles inside the matrix either as large and compact aggregates (R \textless 0.24) or as individual nanoparticles dispersion (R \textgreater 0.24). From the analysis of the interparticles structure factor, we can extract the thickness of the spherical corona of grafted brushes and correlate it with the dispersion: aggregation of the particles is associated with a significant collapse of the grafted chains, in agreement with the theoretical models describing the free energy as a combination of a mixing entropy term between the free and the grafted chains and an elastic term of deformation of the grafted brushes. At fixed grafting density, the individual dispersion of particles below the theoretical limit of R = 1 can be observed, due to interdiffusion between the grafted and the free chains but also to processing kinetics effects, surface curvature and chains poly dispersity. Mechanical analysis of nanocomposites show the appearance of a longer relaxation time at low frequencies, more pronounced in the aggregated case even without direct connectivity between the aggregates. Correlation between the local structure and the rheological behavior suggests that the macroscopic elastic modulus of the nanocomposite could be described mainly by a short-range contribution, at the scale of the interactions between grafted particles, without significant effect of larger scale organizations.

We present several examples of an unexpected behaviour, occurring in different types of polymer networks (permanent or temporary) containing either small or large proportions of mobile species. The spatial fluctuations of local concentration of the mobile probes appear (through neutron scattering experiments) to be anisotropically enhanced (essentially parallel to the elongation axis) when the samples are uniaxially stretched. This behaviour may arise either from an anisotropic enhancement of the thermal fluctuations under strain or from the revealing of «quenched» large scale heterogeneities. It has not been possible yet to decide which of these rather different explanations is the more satisfactory