My research focus on the mechanics and flow of complex materials between fluid and solid, such as particulate media (granular materials, yield-stress fluid, dense suspensions) or biological systems (plants).
The sensor of gravity in plants consists of tiny starch-rich grains called statoliths that sediment and form miniature granular piles at the bottom of the gravisensing cells. How such a sensor could be a reliable clinometer is unclear, as granular materials are known to display jamming and finite avalanche angles. Here we address this issue by comparing statolith avalanches in plant cells to microfluidic avalanches of Brownian particles in biomimetic cells. We reveal that statoliths behave like a liquid, not a granular material, due to the cell activity that strongly agitates statoliths. Our study elucidates the physical grounds of the high sensitivity of plants to gravity and bridges the active microrheology of statoliths to the macroscopic response of the plant.
Bérut et al, Proc. Natl. Acad. Sci. USA (2018) pdf
Plants are sessile organisms without nerves. As such, they have developed specific mechanisms to carry information rapidly throughout their body in response to mechanical stimuli. Recently, it has been suggested that the first stage of this long-distance signaling could be the propagation of hydraulic signals induced by the mechanical deformation of the plant tissue (bending), but the physical origin of this hydro-mechanical coupling remains a conundrum. Here, we address this issue by combining experiments on natural tree branches and soft biomimetic beams with modeling. We reveal a generic non-linear mechanism responsible for the generation of hydraulic pulses induced by bending in poroelastic branches. Our study gives a physical basis for long-distance communication in plants based on fast hydraulic signals.
Louf et al, Proc. Natl. Acad. Sci. USA 114, 11034-11039 (2017) pdf
The sudden and severe increase in the viscosity of certain suspensions above an onset stress is one of the most spectacular phenomena observed in complex fluids. This shear thickening, which has major implications for industry, is a long-standing puzzle in soft-matter physics. Recently, a frictional transition was conjectured to cause this phenomenon. Using experimental concepts from granular physics, we provide direct evidence that such suspensions are frictionless under low confining pressure, which is key to understanding their shear-thickening behavior.
Clavaud et al, Proc. Natl. Acad. Sci. USA 114, 5147-5152 (2017) pdf