Dynamics in stretched nanocomposites

The addition of nanoparticles to a polymermatrix is a well-known process to improve the mechanicalproperties of polymers. Many studies of mechanical reinforcementin polymer nanocomposites (PNCs) focus on rubberymatrices; however, much less effort concentrates on thefactors controlling the mechanical performance of thetechnologically important glassy PNCs. This paper presentsa study of the effect of the polymer molecular weight (MW)on the overall mechanical properties of glassy PNCs withattractive interaction by using Brillouin light scattering. Wefound that the mechanical moduli (bulk and shear) have anonmonotonic dependence on MW that cannot be predictedby simple rule of mixtures. The moduli increase with increasing MW up to 100 kg/mol followed by a drop at higher MW. Wedemonstrate that the change in the mechanical properties of PNCs can be associated with the properties of the interfacialpolymer layer. The latter depend on the interfacial chain packing and stretching, as well as polymer bridging,which vary differently with the MW of the polymer. These competing contributions lead to the observed nonmonotonicvariations of the glassy PNC moduli with MW. Our work provides a simple, cost-effective, and efficient way to control themechanical properties of glassy PNCs by tuning the polymer chain length. Our finding can be beneficial for the rational designof PNCs with desired mechanical performance.

Polymer nanocomposites are mixtures of nanoparticles (NPs) 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 via the surface-modification of the nanoparticles by grafting small hydrophobic molecules (coating agents), which promote the filler-polymer compatibility. In this talk, different ways to obtain information from small-angle scattering on the structure of nanocomposites will be presented using either the recently proposed correlation hole analysis [1] or reverse Monte-Carlo (RMC) analysis giving access to aggregate mass distributions [2]. In particular, we will review recent results on model nanocomposites – and their industrial counterparts – using surface-modified silica NPs with different types of silane groups (tri-ethoxy or mono-methoxy) and silanes of different lengths. To describe NP structure in solvents and after casting in a polymer matrix, we propose a new method which combines SAXS, RMC and aggregate recognition analysis [2]. this analysis suggests that silane molecules with trifunctional grafting functions lead to the formation of polycondensed patches (i.e., reaction of lateral groups with neighboring molecules) on silica surface, favoring attractive interactions. On the other hand, the lowest aggregation is observed using mono-functionalized silane molecules where patches cannot form. Finally, regarding chain structure, a quick outlook on why contrast-matching with SANS in nanocomposites often fails will be proposed [3]. [1] A.-C. Genix and J. Oberdisse, Soft Matter 2017, 13, 8144. [2] D. Musino, A.-C. Genix, T. Chaussée, L. Guy, N. Meissner, R. Kozak, T. Bizien, J. Oberdisse, Langmuir 2018, 34, 3010. [3] A. Banc, A.-C. Genix, C. Dupas, M. Sztucki, R. Schweins, M.-S. Appavou, J. Oberdisse, Macromolecules 2015, 48, 6596.

Polymer nanocomposites (PNCs) are made by dispersion of hard fillers in a polymer matrix, where the fillers are usually added to enhance mechanical properties. Such materials attract industrial interest and their investigation is essential for the improvement of their performances. The present study concerns nanocomposites obtained using hydrophilic silica nanoparticles (NPs) dispersed in a soft polymer matrix of styrene-butadiene, commonly used in car tire manufacturing. The mechanical performances of such PNCs are strongly related to the structural properties: the dispersion state of silica particles in the polymer melt is governed by the mixing protocols (e.g., solid phase mixing or solvent casting) and thermodynamics of the system (i.e., particle miscibility) which influence the filler-filler and the filler-polymer interactions.We have developed a new model nanocomposite system, equivalent to a simplified industrial one [1,2], made by solvent casting technique using colloidal silica NPs. In such model PNCs, the dispersion of colloidal silica is tuned via the surface-modification of silica particles by grafting hydrophobic molecules, i.e., silane coating agents, which promote the filler-polymer compatibility.To describe NP structure in solvents and after casting in a polymer matrix, we propose a new method which combines Small Angle X-ray Scattering (SAXS), reverse Monte Carlo (RMC) and aggregate recognition (AR) analysis [3]. This approach allows obtaining a detailed structural characterization of the silica NPs surface-modified with different silane grafting groups (i.e., tri-ethoxy, tri-methoxy or mono-methoxy silane). In particular, this analysis suggests that silane molecules with trifunctional grafting functions lead to the formation of polycondensed patches (i.e., reaction of lateral groups with neighboring molecules) on silica surface, favoring attractive interactions. On the other hand, the lowest aggregation is observed using mono-functionalized silane molecules where patches cannot form. In the near future, the SAXS-RMC-AR approach will be extended to investigate the structural properties of nanocomposite systems where silica NPs are surface-modified with silane molecules of various alkyl chain [4].[1] D. Musino, A.C. Genix, C. Fayolle, A. Papon, L. Guy, N. Meissner, R. Kozak, P. Weda, T. Bizien, T. Chaussée, and J. Oberdisse,, Macromolecules (2017)[2] G. P. Baeza, A.-C. Genix, C. Degrandcourt, L. Petitjean, J. Gummel, M. Couty, J. Oberdisse, Macromolecules (2013)[3] D. Musino, A.-C. Genix, T. Chaussée, L. Guy, N. Meissner, R. Kozak, T. Bizien, J. Oberdisse, Langmuir (2018)[4] D. Musino et al., in preparation

Despite an abundant literature on epoxy-amine systems, a complete description of the curing kinetics in epoxy-phenol composites was still lacking. In this study, the curing kinetics of an epoxy-phenol composite relevant to microelectronics industry is probed by isothermal and non-isothermal differential scanning calorimetry. An isoconversional analysis of the data reveals a significant contribution of the diffusion of molecular species to the activation energy, at low temperature and high degrees of curing. A model-fitting of the kinetics is performed in two successive steps: high-temperatures data are fitted with Arrhenius law and nth order autocatalytic model (where the diffusion contribution is neglected), whereas low-temperature data are fitted using Rabinowitch and modified-Williams-Landel-Ferry models (considering a diffusion contribution related to the glass transition). The chemical and diffusion contributions to the rate constants are calculated at various temperatures, clarifying the kinetics regimes with precision. Finally, the kinetics regimes are summarized in an improved time-temperature-transformation diagram.

Polymer nanocomposites (PNCs) are made by dispersion of hard fillers in a polymer matrix, where the fillers are usually added to enhance mechanical properties. Thus, such materials attract industrial interest and their investigation is essential for the improvement of their performances.The present study concerns nanocomposites obtained using hydrophilic silica nanoparticles (NPs) dispersed in a soft polymer matrix of styrene-butadiene, commonly used in car tire manufacturing. The mechanical performances of such PNCs are strongly related to the structural properties: the dispersion state of silica particles in the polymer melt is governed by the mixing protocols (e.g., solid phase mixing or solvent casting) and thermodynamics of the system (i.e., particle miscibility) which influence the filler-filler and the filler-polymer interactions.We developed a new model nanocomposite system, equivalent to a simplified industrial one, made by solvent casting technique using colloidal silica NPs. In such model PNCs, the dispersion of colloidal silica is tuned via the surface-modification of silica particles by grafting hydrophobic molecules, i.e., silane coating agents, which promote the filler-polymer compatibility.To describe NP structure in solvents and after casting into polymer matrix, we propose a new method which combines Small Angle X-ray Scattering (SAXS), reverse Monte Carlo (RMC) and aggregate recognition (AR) analysis. This approach allows obtaining a detailed structural characterization of the silica NPs surface-modified with different silane grafting groups (i.e., tri-ethoxy, tri-methoxy or mono-methoxy silane). In particular, we show that silane molecules with trifunctional grafting functions may lead to the formation of polycondensed patches (i.e., reaction of lateral groups with neighboring molecules) on silica surface, favoring attractive interactions. Thus, the lowest aggregation is observed using mono-functionalized silane molecules where patches cannot form.Next, the SAXS-RMC-AR approach will be extended to investigate the structural properties of nanocomposite systems where silica NPs are surface-modified with silane molecules of various alkyl chain.