Aggregate formation and chain structure in polymer nanocomposites

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.