Deswelling and deformation of microgels in concentrated packings

Izabella Bouhid de Aguiar (1, 2) , T. van de Laar (1, 3) , Martine Meireles (2) , Antoine Bouchoux (4) , Joris Sprakel (3) , Karin Schroën (1)

1 Laboratory of Food Process Engineering
2 LGC - Laboratoire de Génie Chimique
3 Physical chemistry and Soft matter group
4 LISBP - Laboratoire d'Ingénierie des Systèmes Biologiques et des Procédés

Increasing the particle density of a suspension of microgel colloids above the point of random-close packing, must involve deformations of the particle to accommodate the increase in volume fraction. By contrast to the isotropic osmotic deswelling of soft particles, the particle-particle contacts give rise to a non-homogeneous pressure, raising the question if these deformations occur through homogeneous deswelling or by the formation of facets. Here we aim to answer this question through a combination of imaging of individual microgels in dense packings and a simple model to describe the balance between shape versus volume changes. We find a transition from shape changes at low pressures to volume changes at high pressures, which can be explained qualitatively with our model. Whereas contact mechanics govern at low pressures giving rise to facets, osmotic effects govern at higher pressures, which leads to a more homogeneous deswelling. Our results show that both types of deformation play a large role in highly concentrated microgel suspensions and thus must be taken into account to arrive at an accurate description of the structure, dynamics and mechanics of concentrated suspensions of soft spheres.

Domaines: Biotechnologies; Génie des procédés

Izabella Bouhid de Aguiar, T. van de Laar, Martine Meireles, Antoine Bouchoux, Joris Sprakel, et al.. Deswelling and deformation of microgels in concentrated packings. Scientific Reports, 2017, 7 (1), 11 p. ⟨10.1038/s41598-017-10788-y⟩. ⟨hal-01606237⟩