Understanding the complex structure of polymer blends filled with nanoparticles (NPs) is the key to designing their macroscopic properties. Here, the spatial distribution of hydrogenated (H) and deuterated (D) polymer chains asymmetric in mass is studied by small-angle neutron scattering. Depending on the chain mass, a qualitatively new large-scale organization of poly(vinyl acetate) chains beyond the random-phase approximation is evidenced in nanocomposites with attractive polymersilica interactions. The silica is found to systematically induce bulk segregation. Only with long H-chains, a strong scattering signature is observed in the q-range of the NP size: it is the sign of interfacial isotopic enrichment, i.e., of contrasted polymer shells close to the NP surface. A quantitative model describing both the bulk segregation and the interfacial gradient (over ca. 10-20 nm depending on the NP size) is developed, showing that both are of comparable strength. In all cases, NP surfaces trap the polymer blend in a non-equilibrium state, with preferential adsorption around NPs only if chain length and isotopic preference towards the surface combine their entropic and enthalpic driving forces. This structural evidence for interfacial polymer gradients will open the road to quantitative understanding of the dynamics of many-chain nanocomposite systems.

Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticles are typically strongly aggregated systems with different levels of spatial organization. The strategy that we developed several years ago to investigate such systems is based on the study of simplified industrial samples with ingredients limited to a strict minimum. On the scale of a micrometric simulation box, tens of thousands of nanoparticles are embedded in the matrix, and their dispersion strongly affects the mechanical properties of the material – and which is reflected in the scattered intensity. A statistical method based on a reverse Monte Carlo solution of this many-parameter problem will be presented, showing that some key features like percolation can be described. [1]Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on the polymer dynamics, and some recent progress – including incoherent neutron spin-echo measurements – will be discussed. [2] Such results may be confronted to dielectric spectroscopy measurements which in some cases are not conclusive due the impossibility to correctly resolve the α-relaxation in presence of strong interfacial polarization processes. An original application of dielectric spectroscopy with a surprising measurement of the adsorption isotherm of coating agents onto silica buried in the polymer matrix will also be discussed. [3]References[1] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907.[2] Musino D, Oberdisse J, Farago B, Alegria A, Genix A-C, ACS Macro Letters 2020, 9:910.[3] Musino D, Oberdisse J, Sztucki M, Alegria A, Genix A-C, Macromolecules 2020, 53:8083.

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Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticles are typically stronglyaggregated systems with different levels of spatial organization, as highlighted by our group in the past [1]. The strategythat we developed these past years was to investigate such systems based on the study of simplified industrial sampleswith ingredients limited to a strict minimum. The analysis of small-angle X-ray scattering data can then be performed onthe scale of a micrometric simulation box. Tens of thousands of “model” nanoparticles are embedded in the matrix, andtheir dispersion strongly affects both the mechanical properties of the material, and the scattered intensity. A statisticalmethod based on a reverse Monte Carlo solution of this many-parameter scattering problem will be presented, showingthat some key features like percolation can be described [2].Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on the polymer structure anddynamics, and some recent progress will be discussed [3]. In particular, we have studied blends of short and long chains,where one chain type is deuterated, by small-angle neutron scattering. Different degrees of spatial segregation could beidentified recently, including a peculiar, “fish-shaped” interfacial gradient characterized also by reverse Monte Carlosimulations, this time of the interface.[1] Guilhem P. Baeza, Anne-Caroline Genix, C. Degrandcourt, Laurent Petitjean, Jérémie Gummel, Marc Couty, Julian Oberdisse, Macromolecules 2013, 46, 317−329(cover article)[2] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907.[3] A.C. Genix, V. Bocharova, B. Carroll, P. Dieudonné-George, M. Sztucki, R. Schweins, A. P. Sokolov, and Julian Oberdisse, ACS Applied Materials and Interfaces,2021, in press

Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticles are typically strongly aggregated systems with different levels of spatial organization, as highlighted by our group in the past [1]. The strategy that we developed these past years was to investigate such systems based on the study of simplified industrial samples with ingredients limited to a strict minimum. The analysis of small-angle X-ray scattering data can then be performed on the scale of a micrometric simulation box. Tens of thousands of “model” nanoparticles are embedded in the matrix, and their dispersion strongly affects both the mechanical properties of the material, and the scattered intensity. A statistical method based on a reverse Monte Carlo solution of this many-parameter scattering problem will be presented, showing that some key features like percolation can be described [2].Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on the polymer structure and dynamics, and some recent progress will be discussed [3]. In particular, we have studied blends of short and long chains, where one chain type is deuterated, by small-angle neutron scattering. Different degrees of spatial segregation could be identified recently, including a peculiar, “fish-shaped” interfacial gradient characterized also by reverse Monte Carlo simulations, this time of the interface.References[1] Guilhem P. Baeza, Anne-Caroline Genix, C. Degrandcourt, Laurent Petitjean, Jérémie Gummel, Marc Couty, Julian Oberdisse, Macromolecules 2013, 46, 317−329 (cover article)[2] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907.[3] A.C. Genix, V. Bocharova, B. Carroll, P. Dieudonné-George, M. Sztucki, R. Schweins, A. P. Sokolov, and Julian Oberdisse, ACS Applied Materials and Interfaces, 2021, in press