Grand Séminaire d'Institut

Lundi 23 Septembre 2024 à 15h30.

Affine hierarchical compaction of beads of colloidal gels

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With their heterogeneous fractal network, colloidal gels represent an ideal sample for investigating the drying process of amorphous solids. Due to the buildup of tensile and compression stresses, colloidal gels fail while drying if they adhere to a substrate. The failure is manifested at the macroscopic scale by extreme events such as delamination or volume-spanning cracks. These events prevent an accurate characterization of the microscopic rearrangement led by the compaction during drying. Here, we avoid cracking by producing boundary-free millimeter-sized beads of a colloidal gel, whose drying process is smooth and homogeneous. To investigate the drying process at the microscopic scale, we developed a novel dynamic light scattering (DLS) setup adapted to probe microscopic dynamics with spatial and temporal resolution for spherical samples. DLS reveals that stresses imposed by drying on the bead surface propagate homogeneously, inducing plastic rearrangements throughout the whole gel volume. Moreover, we characterize the structural evolution of the gel network by performing X-ray scattering. Remarkably, we find that drying gels reorganize hierarchically: the network is first modified at large scales and later at small scales, down to a few particle sizes.

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