Rheology of suspensions in the thermal crossover: an incline plane experiment under confocal observation.

Hard sphere suspensions have been widely studied in the case of frictional athermal spheres as well as in the case of dilute colloidal suspensions. However, the cross-over regime, where frictional and thermal effects are both significant [1], is still lacking of a complete description, despite its crucial importance in understanding realistic flows. Inspired by the macroscopic incline plane experiments which allowed significant progresses in the description of granular flows, we designed a microscopic incline plane experiment under confocal observation, using micron-size suspensions for which the thermal stress is of the same order of magnitude as the gravity stress. We compare the experimental velocity profiles with a theoretical model that extends to pressure-imposed conditions the model of Ikeda et al [2] for the rheology of soft and brownian suspensions at the cross-over of the glass and jamming transition.

[1] A. Bérut, O. Pouliquen, Y. Forterre, Brownian granular flows down heaps, Phys. Rev. Lett., 123, 248005 (2019).
[2] A. Ikeda, L. Berthier, and P. Sollich, Disentangling Glass and Jamming Physics in the Rheology of Soft Materials, Soft Matter 9, 7669 (2013).