Séminaire exceptionnel IUSTI – 7 juillet 2022 – 11h30 salle 250

Insights in dense suspensions by visualizing silica particles with tunable surfaces

Vincent Niggel – ETH Zurich, Suisse

In complex particulate flows, the surfaces of flowing particles undergo both relative translation and rotation. While measuring the (relative) displacements of colloids is quite common, the measurement of their rotation is much less frequent. However, such information is quite important to provide a more complete picture of the details of interparticle contacts under flow or to investigate if rotational and translational degrees of freedom exhibit different dependencies on volume fraction when suspensions approach the glass transition. In our work, we have explored different synthesis paths to create several types of fluorescent silica colloids with tunable roughness and heterogeneous fluorescence, which allow us to track their individual motion (translation or rotation) in dense suspensions. Moreover, we have developed a method that enables us to track the 3D rotation of our particles based on 2D images in a fixed plane, greatly simplifying the acquisition of high-frame-rate videos. Finally, our goal is to image sheared dense suspensions, i.e. with a confocal microscopy in proximity of the zero-velocity plane of a counter-rotating shear cell, in order to directly characterize the interactions between the particles under flow conditions.