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International audience; Polymer nanocomposites are mixtures of nanoparticles and polymer chains, where the filler particles are usually added to enhance mechanical properties, e.g. of car tire materials. Performance depends to a great extent on the structure of the filler, i.e. its dispersion state in the polymer matrix, which itself depends on mixing protocols, but also on the thermodynamics of the system. The latter can be tuned by performing either chemical surface modifications of the nanoparticles, or by playing with the mass and/or grafting properties of the polymer chains. In this talk, some straightforward ways to obtain information from small-angle scattering on the structure of nanocomposites will be presented [1]. In particular, we will review recent results on nanocomposites close to industrial applications, including what is probably one of the first quantitative analyses of such disordered structures by a combination of SAXS, TEM and numerical simulations [2]. This analysis will then be applied to the impact of small molecules on such structures [3]. Concerning chain structure, a quick outlook on why contrast-matching with SANS in nanocomposites often fails will be proposed [4]. REFERENCES1.A.-C. Genix and J. Oberdisse, Structure and dynamics of polymer nanocomposites studied by X-ray and neutron scattering techniques. Current Opinion in Colloid & Interface Science 2015, 20, 293-303 (2015).2. G. P. Baeza, A. C. Genix, C. Degrandcourt, L. Petitjean, J. Gummel, M. Couty and J. Oberdisse, Multiscale Filler Structure in Simplified Industrial Nanocomposite Silica/SBR Systems Studied by SAXS and TEM, Macromolecules, 46, 317-329 (2013).3. D. Musino, A.-C. Genix, C. Fayolle, A. Papon, L. Guy, N. Meissner, P. Weda, T. Bizien, T. Chaussée, J. Oberdisse, Synergistic effect of small molecules on large-scale structure of simplified industrial nanocomposites, submitted.4. A. Banc, A.-C. Genix, C. Dupas, M. Sztucki, R. Schweins, M.-S. Appavou, J. Oberdisse, Origin of small-angle scattering from contrast-matched nanoparticles: A study of chain and filler structure in polymer nanocomposites, Macromolecules, 48, 6596−6605 (2015).

International audience; The structure of polymer nanocomposites has important consequences on final properties, like e.g.mechanical reinforcement. The structure of the hard filler phase is usually characterized by electronmicroscopy and small-angle X-ray scattering (SAXS), and we will review recent examples of fillerstructure in model and industrial nanocomposites. The chain conformation can only bemeasured by small-angle neutron scattering (SANS) with isotopic substitution. Over the past 15 years,considerable efforts have been dedicated to such measurements. Results appear to converge towardGaussian statistics of chains, unperturbed by the presence of filler NPs, and exceptions seem to be dueto system-dependent effects. In nearly all studies, however, unexplained pollution of the scatteringdata in the low-q range has been observed, in spite of careful contrast-matching.In this study, the conformation of polymer chains in silica-latex nanocomposites has been studiedunder zero-average contrast (ZAC) conditions using SANS. Samples have been prepared by dryingcolloidal suspensions of silica and polymer nanoparticles (NPs) for two different silica NPs (radius of5 and 15 nm) and two chain masses (17 and 100 kg/mol). By mixing appropriate amounts ofhydrogenated and deuterated polymer, chain scattering contrast is introduced, and in principle silicascattering is suppressed. However, the SANS scattering intensities displayed distinct deviations at lowangles. Comparison of the SANS and SAXS intensities proves that the measurement of chain structureby SANS is perturbed by unwanted silica contributions, i.e., the silica is ‘mysteriously’ visible. Aquantitative model rationalizing these contributions for the first time is proposed. It is based on astatistical H/D-mismatch in the local environment of the silica NPs. Such a mismatch leads to theexistence of a nanometer-thick polymer shell surrounding silica NPs, which carries H/D contrast andthereby produce an undesired scattering contribution. These shells are presumably maintained by thereduced mobility of polymer close to interfaces or attractive polymer-silica interactions. The effect ofunwanted filler scattering is NP size-dependent − it is pronounced only for smaller beads. This isprobably why ZAC turned out to be so difficult with polymer nanocomposites.

International audience; In this talk, some straightforward ways to obtain information from small-angle scattering on the structure of complex systems, in particular nanocomposites, will be given [1]. Polymer nanocomposites are mixtures of nanoparticles and polymer chains, where the particles – called filler – are usually added to enhance mechanical properties, like e.g. in car tires. Performances depend to a great extent on the structure of the filler, i.e. their dispersion state in the polymer matrix, which itself depends on mixing protocols, but also on the thermodynamics of the system. The latter can be tuned by performing either chemical surface modifications of the nanoparticles, or by playing with the mass and/or grafting properties of the polymer chains.We will present recent results on nanocomposites close to industrial applications, including what is probably one of the first quantitative analyses of such disordered structures by a combination of SAXS, TEM and numerical simulations [2]. The study led to the identification of a unique structure-determining parameter [3]. The generalization of the above-mentioned approach – the correlation hole analysis – will furthermore be illustrated by structural studies by small angle scattering of well-defined model systems, showing the influence of chain mass [4] or surface grafting of small molecules [5]. Finally, if the chairman is nice, a quick outlook on why contrast-matching with SANS in nanocomposites often fails will be proposed [6].[1] A.-C. Genix and J. Oberdisse, Structure and dynamics of polymer nanocomposites studied by X-ray and neutron scattering techniques. Current Opinion in Colloid & Interface Science, 2015, 20, 293-303.[2] G. P. Baeza, A. C. Genix, C. Degrandcourt, L. Petitjean, J. Gummel, M. Couty and J. Oberdisse, Macromolecules, 2013, 46, 317-329.[3] G. P. Baeza, A.-C. Genix, C. Degrandcourt, J. Gummel, A. Mujtaba, K. Saalwächter, T. Thurn-Albrecht, M. Couty, and J. Oberdisse, ACS MacroLetters, 2014, 3 (5), 448–452[4] A. Banc, A. C. Genix, M. Chirat, C. Dupas, S. Caillol, M. Sztucki and J. Oberdisse, Macromolecules, 2014, 47, 3219–3230.[5] C. Schmitt Pauly, A.-C. Genix, J. G. Alauzun, M. Sztucki, P. H. Mutin and J. Oberdisse, Polymer, in press.[6] A. Banc, A.-C. Genix, C. Dupas, M. Sztucki, R. Schweins, M.-S. Appavou, J. Oberdisse, Macromolecules 2015, 48, 6596−6605.

International audience; The structure of polymer nanocomposites has important consequences on final properties, like for instance mechanical reinforcement. The structure of the hard filler phase is usually characterized by electron microscopy and small-angle X-ray scattering, and we will review recent examples of filler structure in model [1] or industrial nanocomposites [2]. The chain conformation can only be measured by small-angle neutron scattering (SANS). Continuous efforts over the past 15 years have produced a body of sometimes contradictory, because system-dependent, results, see e.g. [3]. In virtually all studies, however, a mismatch ruining the polymer form factor at low-angles has been observed, in spite of careful contrast-matching. In this study, the conformation of polymer chains in silica-latex-nanocomposites has been studied under zero-average contrast conditions using SANS. Samples have been prepared by drying colloidal suspensions of silica and polymer nanoparticles (NPs) for two different silica NPs (radius of 5 and 15 nm) and two chain molecular weights (17 and 100 kg/mol). By appropriate mixing of hydrogenated and deuterated polymer, chain scattering contrast is introduced, and in principle silica scattering suppressed. The silica structure consisting mostly of small fractal aggregates is characterized by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) on the same samples. The measurement of the chain structure by SANS, however, is perturbed by unwanted silica contributions, as often reported in the literature. Here, the contribution of contrast-matched silica is evidenced as a function of system parameters, namely chain mass, silica size, and volume fraction, and a model rationalizing these contributions for the first time is proposed. Via a statistical model, a nanometer-thick polymer shell surrounding silica NPs is shown to create contrast, which is presumably maintained by the reduced mobility of polymer close to interfaces or attractive polymer-silica interactions. This shell is proven to be quantitatively important only for the smallest silica NPs. As a consequence, the pure polymer scattering can be isolated, and the polymer radius of gyration is found to be independent of filler content and NP size [4].[1] A. Banc et al, Macromolecules 2014, 47 (9), 3219–3230 [2] G. Baeza et al, Soft Matter 2014, 10, 6686-6695.[3] A.C. Genix and J. Oberdisse, Current Opinion in Colloid and Interface Science, 2015, in press. [4] A. Banc et al, Macromolecules 2015, 48, 6596−6605.

In this thesis, we study nanocomposite materials made of rubber (styrene-butadien copolymer "SBR") reinforced by highly dispersible silica nanofillers. In order to identify physico-chemical mechanisms responsible for such a reinforcement and being able to optimize it, we must understand existing correlations between the material macroscopic properties and the multi-scale structure of the filler. For this purpose, a wide campaign of small angle X-ray scattering (SAXS) and electronic microscopy experiments have been performed. Coupling this data with Monte-Carlo simulations led to the emergence of a concept describing the silica morphology: A branched tridimensional network built up from aggregates (radius  50 nm) made of nanoparticles (radius  10 nm) spreading across in the whole sample. The analysis of the reinforcement in nanocomposites is based on rheometry and dynamic mechanical analysis. Other techniques like dielectric spectroscopy, nuclear magnetic resonance, thermogravimetric analysis or infra-red spectrometry contributed as well to fully characterize these materials, particularly to probe the SBR chains dynamic at the interface with the filler. In order to reveal the correlations between structure and properties, we systematically described the impact of key parameters such as filler fraction, polymer grafting or the chain molar mass on the silica morphology (aggregates size, ...) as well as on the mechanical behavior (elastic modulous, ...) of the composites. This work allowed identifying the polymer grafting density as the parameter defining the filler structure and playing a significant role on the reinforcement. This thesis, firmly focused on fundamental comprehension, contributes to the development of a general law describing the effect of the filler structure on the performance of tires. The latter must provide answers to engineering issues concerning wear resistance, wet grip or rolling resistance. Moreover, in order to obtain additional information regarding the rubber-silica interactions, we developed an experimental process allowing the production of "model" systems reinforced with colloidal silica. The use of such filler, very well defined in terms of size and shape, makes much easier the structural analysis giving the opportunity to investigate deeper the effective potential between the two phases during the composite production., Cette thèse propose l'étude de matériaux composites industriels simplifiés constitués de caoutchouc non réticulé (copolymère styrène-butadiène " SBR ") renforcés par des charges nanométriques de silice hautement dispersible. Afin d'identifier les mécanismes physico-chimiques responsables de ce renforcement et être capable de l'optimiser, nous devons comprendre les corrélations existantes entre les propriétés macroscopiques du matériau et la structure des charges à différentes échelles. Pour cela, une large campagne d'expériences de diffusion des rayons-X aux petits angles (DXPA) ainsi que de nombreux clichés de microscopie électronique ont été réalisés. En couplant ces données avec des simulations Monte-Carlo, il a été notamment possible de mettre en avant la présence d'une organisation à trois niveaux en partant de billes élémentaires d'une dizaine de nanomètres formant des agrégats eux-mêmes arrangés selon un réseau tridimensionnel branché existant à travers tout l'échantillon. L'analyse du renforcement dans les nanocomposites a été effectuée par rhéométrie et analyse dynamique mécanique. D'autres techniques telles que la spectroscopie diélectrique, la résonnance magnétique nucléaire, l'analyse thermogravimétrique ou la spectrométrie infrarouge ont également contribué à une caractérisation complète de ces matériaux, en particulier pour sonder la dynamique des chaînes de SBR à l'interface avec la charge. Afin de déceler les corrélations existantes entre structure et propriétés, nous nous sommes attachés à décrire systématiquement l'influence de paramètres-clés tels que la fraction volumique en silice, le type de polymère employé (greffable sur la silice ou pas) ou leur masse molaire sur la morphologie des charges (par exemple la taille des agrégats) ainsi que sur le comportement mécanique (par exemple leur module d'élasticité) des composites. Ce travail a permis d'identifier la densité de greffage des chaines comme le paramètre définissant la structure des composites et impactant significativement le renforcement. Cette thèse, résolument tournée vers la compréhension fondamentale, est aussi une contribution à la recherche d'une loi de comportement décrivant l'effet de la structure des charges sur les performances des pneumatiques. Cette dernière doit permettre de répondre à des problématiques rencontrées en ingénierie telles que la résistance à l'usure, l'adhérence, ou la résistance au roulement. De plus, dans le but d'atteindre des informations supplémentaires quant aux interactions entre caoutchouc et silice, nous avons mis au point un protocole expérimental permettant de formuler des échantillons dits " modèles " renforcés avec une silice colloïdale. Cette dernière étant beaucoup mieux définie d'un point de vue géométrique, son analyse structurale est grandement facilitée rendant possible l'étude des potentiels mis en jeu pendant la production des nanocomposites.

National audience; The structure of polymer nanocomposites has important consequences on final properties, like for instance mechanical reinforcement. While the structure of the hard filler nanoparticles (NPs) is usually characterized by electron microscopy and small-angle X-ray scattering (SAXS), the chain conformation can only be measured by small-angle neutron scattering (SANS). Two main difficulties may arise with such a structural analysis. First of all, extracting reliable structural information on filler dispersion may be hindered by lack of a priori knowledge of the system. In this talk, we will discuss two examples. In the first one, additional knowledge is due to the model character of well-characterized NPs, and it can be used to analyze scattering data using Monte Carlo simulations [1]. In the second one, industrial filler NPs of high structural complexity have been used, and structural characterization of this system was only possible by quantitatively combining MC simulations, transmission electron microscopy, and SAXS [2]. Concerning the determination of polymer conformation by SANS, a second and mostly unforeseen difficulty shows up: in spite of great care in contrast-matching (undesired) NP contributions to the SANS signal, such additional intensities are systematically found in the literature. Two model cases are discussed in this talk: the first one emphasizes large-scale polymer heterogeneities reminiscent of the solution structure before nanocomposite formation. This structure is described quantitatively by a ‘hairy bead’ model [3]. The second one, finally, is the result of a general study of incomplete filler NP matching, evidencing for the first time that smallest NPs may induce statistical fluctuations in H-D-density in a surrounding shell, making in principle matched filler visible. Incidentally, the typical size of such mismatched polymer shells is deduced from the data [4]. [1] A. Banc et al, Macromolecules 47 (9), 3219–3230 (2014); J. Oberdisse et al Soft Matter, 3, 476-485 (2007)[2] G. Baeza et al, Soft Matter 10, 6686-6695 (2014)[3] A.C. Genix et al, Macromolecules 45(3), 1663-1675 (2012)[4] A. Banc et al, submitted

International audience

International audience; Nanocomposites made of hard inorganic nanoparticles (NPs) embedded in a soft polymer matrix may have rheological properties of interest for various applications, and in particular car tires. These properties depend crucially on the dispersion of the filler NPs, which has been studied in simplified industrial (i.e., without crosslinker and related chemistry) styrene–butadiene nanocomposites with silica filler NPs. We have developed a quantitative structural analysis based on a combination of electron microscopy, Monte Carlo simulations, and small-angle X-ray scattering. It allowed us to establish a global structural model, where primary silica beads are organized within small aggregates, which themselves fill large-scale fractal branches. Experimental parameters have been varied independently, starting with the silica volume fraction si, the matrix composition (percentage of graftable chains), and the chain mass. The grafting density on the silica NPs was shown to be the structure- and rheology-determining parameter, and we will show that a simple mechanism is able to explain the evolution of aggregate size and mass with grafting density. Moreover, dynamical properties have been followed by broadband dielectric spectroscopy (BDS) recently, and the detailed characterization of two high-temperature silica-related processes provided evidence that one of them can be linked to the structural evolution of these nanocomposites. Our work thus suggests that such high-temperature BDS-measurements can be used to detect reorganizations in structurally complex silica nanocomposites.Baeza et al, Macromolecules 2013, ibid 2013, ACS Macro Letters 2014, Soft Matter 2014

International audience; Mixing inorganic nanoparticles (ca. 10-20 nm) with polymer leads to the formation of nanocomposites. Their main reason of existence is that they combine the best of both worlds, i.e. nanoparticle strength and polymer flexibility, which has important applications, e.g. for the car tire industry. In this talk, a simplified industrial model system based on filler particles of industrial origin but with a highly reduced chemistry will be presented. It is generally recognized that the filler structure has a strong impact on the rheological properties, and it is thus important to be able to characterize it in detail. Here, microscopic observations of the dispersion of the nanoparticles in the polymer matrix by electron microscopy and scattering will be discussed and related to the microscopic structure to their macroscopic rheological properties. The structure of SBR-silica nanocomposites designed to reproduce key features of industrial samples, but of simplified composition, has been studied on length scales extending from the nanometric primary particles to microns. We propose an original method for scattering data analysis of such multi-scale systems by including self-consistent polydisperse form and structure factors of aggregates [1]. The complex structure of the silica within the nanocomposites is quantitatively modeled in a step-by-step manner, starting with the primary silica beads as basic building units (10 - 20 nm range). These beads are found to be aggregated in small clusters, the typical radius of which is in the 40 nm range. These aggregates are themselves concentrated in large-scale fractal branches (thickness ca. 150 nm, extending over microns), cf. the TEM cliché below. A quantitative analysis of the TEM data is used to estimate the volume fraction of fractal branches, which is an input for structure factor calculations of aggregates inside branches using numerical simulations as indicated in the Figure on the right. Then, the influence of polymer grafting is explored, yielding a strong effect on the aggregate mass [2]. In parallel, the rheological properties of these silica structures in the SBR-matrix are characterized with oscillatory shear. The resulting reinforcement curve of the high-frequency storage modulus can be described using a combination of hydrodynamic reinforcement for silica fraction below a critical percolation fraction, and a percolation law above. It is interesting to note that the aggregate compacity obtained from the structural analysis (SAXS and TEM) is fully compatible with the reinforcement data.

Structure de nanocomposites industriels simplifiés fortement chargés

National audience; Nous proposons l'étude de matériaux composites industriels simplifiés constitués de caoutchouc non réticulé (copolymère styrène-butadiène " SBR ") renforcés par des charges nanométriques de silice hautement dispersible. Afin d'identifier les mécanismes physico-chimiques responsables de ce renforcement et être capable de l'optimiser, nous devons comprendre les corrélations existantes entre les propriétés macroscopiques du matériau et la structure des charges à différentes échelles. Pour cela, une large campagne d'expériences de diffusion des rayons-X aux petits angles (DXPA) ainsi que de nombreux clichés de microscopie électronique ont été réalisés. En couplant ces données avec des simulations Monte-Carlo, il a été notamment possible de mettre en avant la présence d'une organisation à trois niveaux en partant de billes élémentaires d'une dizaine de nanomètres formant des agrégats eux-mêmes arrangés selon un réseau tridimensionnel branché existant à travers tout l'échantillon. Afin de déceler les corrélations existantes entre structure et propriétés, nous nous sommes attachés à décrire systématiquement l'influence de paramètres-clés tels que la fraction volumique en silice, le type de polymère employé (greffable sur la silice ou pas) ou leur masse molaire sur la morphologie des charges (par exemple la taille des agrégats) ainsi que sur le comportement mécanique (par exemple leur module d'élasticité) des composites. Ce travail a permis d'identifier la densité de greffage des chaines comme le paramètre définissant la structure des composites et impactant significativement le renforcement. Ces travaux résolument tournés vers la compréhension fondamentale, sont aussi une contribution à la recherche d'une loi de comportement décrivant l'effet de la structure des charges sur les performances des pneumatiques. Cette dernière doit permettre de répondre à des problématiques rencontrées en ingénierie telles que la résistance à l'usure, l'adhérence, ou la résistance au roulement.

Since 1992 and the apparition of highly dispersible silica as a nanofiller in the green-tire formulation, the structure and dynamics of precipitated silica-SBR nanocomposites produced by solid phase mixing is of a great interest for manufacturers. In this work, we make use of SAXS and TEM to investigate the organization of silica nanoparticles (Rsi 10nm) varying the filler fraction while dynamics is studied by broadband dielectric spectroscopy (BDS) and rheology. The structural analysis of such complex materials revealed a multi-scale filler organization based on a 3D fractal network built up from aggregates made of nanoparticles [1]. The characteristics (size, average aggregation number, compacity...) of such aggregates are extracted from a combined analysis of SAXS and TEM data taking into account the aggregate polydispersity (Nagg50, 35%). Jointly with mechanical experiments, this analysis enables us to estimate the critical aggregation volume fraction at which the network fully percolates (Figure 1a). In the same context, the ionic conductivity () measured by BDS at high temperature displays a jump from 12.7% of silica that we associate with the percolation threshold observed in rheology (Figure 1b). Moreover, at lower temperatures, a Maxwell-Wagner-Sillars process related to the charges blocked at the interface between silica and polymer is observed at temperatures higher than the glass transition in the nanocomposites.