Experimental setup to measure the mechanical properties of colloidal monolayers

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Colloidal monolayers, i.e. two-dimensional assemblies of microscopic particles, are a fascinating testbed to mimic the mechanical properties of complex atomic structures including polycrystalline and glassy phases. In contrast to atoms, microparticles offer the outstanding benefit of being easily observable and deformable. We hereby request funding for a customised instrument to measure the mechanical properties of colloidal monolayers and link them to the motion of the individual particles. Monolayers are prepared at flat liquid-liquid interfaces to harness the high adsorption energies and ensure that the motion is confined in two dimensions. We will study the response to novel mechanical deformations and shear rates spanning more than twelve orders of magnitude. The first key objective of the project (O1) is to gain insight into the physics of impacts in colloidal targets where momentum transfer between microparticles is relevant. To date, momenta cannot be transferred via elastic collisions between microparticles due to the negligible role of inertia in colloidal systems. Here, we use laser ablation to set colloids into motion at unprecedented velocities and study the impact propagation in the dense microstructures. The second key objective (O2) is to investigate, at the single-particle level, the structural evolution of colloidal monolayers under rheometric flows. Classical rheology works in three dimensions and therefore rarely gives insights on the single-particle dynamics. We will focus our attention on interfaces made of Brownian and active particles to unveil the rheological response of synthetic active matter. In order to trigger the above-mentioned deformations and simultaneously image the motion of the individual microparticles, the proposed instrument will include the following built-in components: a Langmuir compression system, an interfacial magnetic agitator, a high-speed camera, pulsed-laser source and a spatial light modulator. Furthermore, we request a a physical vapour deposition system to prepare the colloidal particles of interest. The instrument will be also employed for internal collaboration aimed at understanding the mechanical response of binary mixtures of soft and hard colloids and stimulated sedimentation of colloidal glasses.