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).