EINS experiments were carried out on PNIPAM microgel suspensions with PNIPAM mass fractions of 43, 50, 60, 70, and 95% (dry sample). To single out the incoherent signal from PNIPAM hydrogen atoms, samples were prepared in D2O. Measurements were performed at the backscattering spectrometer IN13 of the ILL. PNIPAM samples were measured inside flat aluminum cells (3.0 cm × 4.0 cm), sealed with an In o-ring. The thickness of the cell was adjusted to achieve a transmission of about 88% for each sample. To obtain samples with the required PNIPAM concentration within the cell used at IN13, we started from the prepared microgel dispersion at 10%. We then proceeded by evaporation of the exceeding D2O in dry atmosphere using a desiccator under moderate vacuum (~ 10 mmHg). Once the final concentration was reached, cells were sealed and left to homogenize at room temperature for at least 4 days before analysis. The sample at 95% composition was prepared from film casting the PNIPAM dispersion at 10% up to dryness in a petri dish. The obtained transparent films were milled with an IKA MF 10.1. Cutting-grinding gave rise to a rough powder that was poured into an aluminum cell for neutron scattering. The weight of each sample was checked before and after the measurement without observing any appreciable variation. Moreover, after EINS measurements, the cells were opened and no changes in the sample morphology were detected, showing a homogeneous character and no compartmentalization effects. EINS data were acquired in the fixed-window elastic mode, thus collecting the intensity elastically scattered as a function of Q. Data were corrected to take into account incident flux, cell scattering, and self-shielding. The intensity of each sample was normalized with respect to a vanadium standard to account for the detector efficiency. Multiple scattering processes were neglected.

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