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Structure and Dynamics of magnetic ellipsoids monolayers under shear (STRUDEL)

Subject Area Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
Term since 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 550416456
 
2D systems of interacting colloids are widely studied because of their industrial applications, but also because of their suitability for modelling crystals and gels. Most of the studies to date have focused on spherical microparticles at equilibrium. Recent advances in the fabrication of field-responsive colloids are paving the way for the study of much richer out-of-equilibrium systems. While the melting of 2D crystals of spheres has been characterised, the effect of particle anisotropy remains elusive and only hinted at. Microellipsoids (ME) are the simplest anisotropic colloids, exemplifying a wide variety of systems ranging from polymeric materials to active systems such as bacteria or actin filaments. However, the relationship between their 2D structuring dynamics and their out-of-equilibrium (OoE) evolution has been little explored. With this experimental project, we aim to fill this gap by quantitatively characterising the dynamics of magnetic ME monolayers driven OoE. In a first phase, confinement at liquid-liquid interface will ensure the formation of two-dimensional systems of magnetic ME. A magnetic field will allow to tune the repulsive interactions in order to i) create crystals with reproducible initial structures and controlled periodicity at large magnetic fields, and ii) easily study melting upon the magnetic field reduction. This will enable the study of static (positional order) and dynamic (rearrangements) properties by video microscopy, thus characterizing the melting phase transition for a closed system of passive ellipsoids. Secondly, an external in-plane shear will be applied to the same system and the corresponding interfacial rheology will be measured for different shearing protocols using optical tweezers. The roto-translational rearrangements and non-affine dynamics of the ME will be quantified as well, thus allowing to explore the rich interplay between micrometric dynamics and mechanical properties of the whole system. To the best of our knowledge, the output of this project will be the first experimental characterization of the melting dynamics of 2D crystals of anisotropic colloids, where time-resolved sample visualization will allow a direct study of the correlation between dynamics and mechanical properties. We believe that our results will allow to elucidate the peculiarities of particles anisotropy in the paths towards 2D crystal melting in OeE conditions.
DFG Programme Research Grants
International Connection France
Cooperation Partner Professor Dr. Maurizio Nobili
 
 

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