Giuliano Zanchetta - Of microgels and particles: trapping, yielding, sliding and swelling in water..

This talk was part of the Thematic Programme on "Non-equilibrium Processes in Physics and Biology" held at the ESI August 19 -- October 11, 2024.

The relevance of soft materials for our daily life is strongly nested in their multiple length scales and rich mechanical behavior, viscoelastic response and flow properties. In particular, yield stress materials (widespread in food, personal care products, biological networks) resist like solids when they are subjected to small stresses, while they flow like liquids when the stress exceeds a threshold value. For this reason, they are also able to trap density-mismatched particles. A paradigmatic example of yield stress material is provided by a suspension of swollen microgels, which can fill the space at low mass concentration.

I will discuss our recent advances in the understanding and control of the interplay between structure, microscale response and macroscale behavior in microgel suspensions, along three main axes:

(i) we tune the stress exerted onto solid inclusions, either through optical forces or through centrifugation, to investigate the conditions for particle (un)trapping and microgel rearrangement across the yielding transition [1];

(ii) we investigate the modes of motion of microgel droplets on inclined, lubricant-impregnated surfaces [2];

(iii) we study the degree of swelling of microgel particles in water and non-aqueous solvents and its impact on their rheology at low and high concentrations.

[1] Vitali et al. Soft Matter 17, 3105 (2021);

[2] Carneri et al. JCIS 644, 487 (2023).