The SoftComp partner CNRS Montpellier, France (Laboratory Charles Coulomb Laboratory, CNRS and University of Montpellier) and the Center for Soft Matter Research at New York University have shed light on the microscopic origin of fluidization, a phenomenon where complex fluids transition from a solid-like state to a flowing state when subjected to external forces.
To achieve this, the team studied concentrated colloidal suspensions and emulsions, soft and amorphous solids made up of micron-sized particles or droplets, highly compressed and dispersed in a solvent. They employed a novel approach, illuminating the samples with a laser while applying cyclic shear deformation. By analysing the temporal fluctuations of the light scattered by the samples, the researchers established a link between the sample’s macroscopic mechanical deformation and a transition between two distinct microscopic dynamic states of matter, characteristic of solid and fluid behaviours.
The modelling of the experimental results was inspired by the work of Dutch physicist J.D. van der Waals, who over a century ago explained the transition between equilibrium states from liquid to gas phase. By adapting van der Waals’ concepts to their systems, the scientists proposed a model in which the dynamics of adjacent regions of a soft solid subjected to shear are coupled, in the same way van der Waals molecules interact with each other, while the amplitude of the imposed deformation plays the same role as depressurization in simple liquids.
