Ref HAL: hal-01408800_v1
Ref Arxiv: 1811.08158
DOI: 10.1016/j.eurpolymj.2016.08.028
WoS: 000390497100051
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11 Citations
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A large body of experimental work on the microstructure and dynamics of simplifiedindustrial nanocomposites made of disordered silica filler in a styrene-butadiene matrixby solid-phase mixing is regrouped and critically discussed in this feature article. Recentresults encompass systems with varying polymer mass, grafting functionality, and fillercontent. They have been obtained by simulation-based structural modelling of nanoparticleaggregate size and mass deduced from small-angle scattering and transmission electronmicroscopy. Our model has been validated by independent swelling experiments.Comparison of structurally-close nanocomposites of widely different chain mass led tothe identification of a unique structure-determining parameter, the grafting density, aswell as to a unified picture of aggregate formation mechanisms in complex nanocompositesduring mixing. In addition, low-field proton NMR allowed for the characterization ofdynamically slowed-down (‘glassy’) polymer layers, which were shown not to dominatethe rheological response, unlike the structural contribution. Finally, broadband dielectricspectroscopy was used in an innovative manner to identify filler percolation – also identifiedby rheology – via dynamics along filler surfaces.

Ref HAL: hal-01317973_v1
DOI: 10.1016/j.polymer.2016.04.073
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Alumina-coated silica nanoparticles (NPs) grafted with phosphonic acids of different hydrophobicitywere used as filler in poly(ethylacrylate) nanocomposites. Phosphonic acids bearing short alkyl chains ora diethylene glycol group have been grafted at densities up to 3.2 P/nm2 on NPs (20 nm) dispersed inwater. Nanocomposites at particle fractions up to 10 vol% have been formulated by casting from thecolloidal mixtures of modified NPs and nanolatex in water. The dispersion of the NPs in the polymermatrix has been studied by TEM combined with small-angle scattering, evidencing aggregation of NPs.TEM shows micrometer-scale inhomogeneities depending on the surface/polymer matrix compatibility.For the local interparticle correlations, a quantitative analysis of the intensity based on the mapping ontothe effective structure factor of polydisperse hard spheres is developed. This mapping allows the modelfreedetermination of the internal volume fraction of aggregates, termed compacity k, to between 10%and 30%, compatible with the TEM analysis. k is found to increase for the higher particle volume fractions,to decrease with grafting density, and to be mostly independent of the nature and mass of thegraft. Preliminary evidence for an improved compatibility of grafted with respect to bare NPs is found, asopposed to their aqueous precursor suspensions where some pre-aggregation is induced by grafting.

Ref HAL: hal-01307989_v1
DOI: 10.1039/C5FD00117J
WoS: 000374440100019
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13 Citations
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Polymer nanocomposites are used widely, mainly for the industrial application of car tyres. The rheological behavior of such nanocomposites depends in a crucial way on thedispersion of the hard filler particles – typically silica nanoparticles embedded in a soft polymer matrix. It is thus important to assess the filler structure, which may be quitedifficult for aggregates of nanoparticles of high polydispersity, and with strong interactions at high loading. This has been achieved recently using a coupled TEM/SAXSstructural model describing the filler microstructure of simplified industrial nanocomposites with grafted or ungrafted silica of high structural disorder. Here, wepresent an original method capable of reducing inter-aggregate interactions by swelling of nanocomposites, diluting the filler to low-volume fractions. Note that this isimpossible to reach by solid mixing due to the large differences in viscoelasticity between the composite and the pure polymer. By combining matrix crosslinking,swelling in a good monomer solvent, and post-polymerization of these monomers, it isshown that it is possible to separate the filler into small aggregates. The latter have then been characterized by electron microscopy and small-angle X-ray scattering,confirming the conclusions of the above mentioned TEM-SAXS structural model applied directly to the highly loaded cases.

Ref HAL: hal-01297463_v1
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The structure of polymer nanocomposites has important consequences on final properties, like for instance mechanical reinforcement. While the structure of the hard filler phase is usually characterized by electron microscopy and small-angle X-ray scattering, the chain conformation can only be measured by small-angle neutron scattering (SANS).

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Ref HAL: hal-01297480_v1
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Les nanocomposites de polymère sont des matériaux dont la matrice polymère est renforcée par des nanoparticules (NPs), comme par exemple des NPs de silice. Pouvoir contrôler la structuration de ces dernières au sein de la matrice est un vieux rêve, parce que l’on espère pouvoir ajuster les propriétés macroscopiques via la microstructure. Dans un premier temps, nous montrerons quelques exemples d’analyse structurale de nanocomposites par diffusion de rayonnement aux petits angles, simulation numérique, et microscopie électronique [1]. Ces études mettent en évidence le caractère en partie hors équilibre de ces structures. Ces dernières années, un paramètre de contrôle des structuration des NPs à l’équilibre est apparu [2-4] : le greffage de chaînes de polymère à la surface des NPs. Il permet de contrôler l’agrégation des NPs, et d’obtenir des structures anisotropes essentiellement visualisées par TEM. Même si cela n’a pas encore trouvé d’écho dans la littérature de mode, la coiffure semble donc être liée au rangement, au moins pour les toutes petites billes. Pour finir, nous discuterons d’un modèle structural développé pour des systèmes plus proches des applications industrielles, et nettement moins enclins à une structuration ordonnée, malgré les efforts de greffage [5]. Références: 1 A. Banc, A.-C. Genix, M. Chirat, C. Dupas, S. Caillol, M. Sztucki, J. Oberdisse, Macromolecules 2014, 47 (9), 3219–32302 A. El Harrak, G. Carrot, J. Oberdisse, Ch. Eychenne-Baron, F. Boué, Macromolecules 2004, 37, 6376-63843 P. Akcora et al, Nature Mat 2009, 8, 354-3594 S. Kumar, N. Jouault, B. Benicewicz, T. Neely Macromolecules 2013, 46, 3199-32145 G. P. Baeza, A.-C. Genix, C. Degrandcourt, L. Petitjean, J. Gummel, M. Couty, J. Oberdisse, Macromolecules 2013, 46, 317−329