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Model systems of nanocomposites are important for our understanding of the structural and dynamical contributions of the constituents to macroscopic properties, and in particular mechanical reinforcement. We study silica-latex nanocomposites obtained from drying an aqueous colloidal mixture of polyacrylate nanolatex and silica nanoparticles. In these systems, the filler microstructure is controlled by the precursor solution pH and it is possible to work at constant aggregation number for different filler fractions [1]. We have followed the evolution of the polymer structure during nanocomposite formation and annealing using small angle neutron scattering under zero-average contrast conditions for the silica nanoparticles. The progressive disappearance of the latex beads by chain interdiffusion and release in the nanocomposites is analyzed with a model for the scattered intensity of hairy latex beads and an RPA description of the free chains (see Figure 1). In silica-free matrices and nanocomposites of low (7%v) and high (20%v) silica content, the annealing procedure results in a molecular dispersion of chains. However, the interdiffusion of individual chain is delayed in presence of 20% of silica. The radius of gyration was not found to be affected by the silica loading in these samples with similar aggregation state (typically ten primary silica particles per aggregate, percolating at high concentration). [2] This important result opens the way for a systematic study of the chain structure in complex environments. Fig.1: Modelling of the structural evolution of the polymer chains in nanocomposites during annealing. References [1] M. Tatou et al., Macromolecules 44, 9029 (2011) [2] A.C. Genix et al., Macromolecules 45, 1663 (2012)