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PhD defense - Jean-Baptiste Thomazo
08
OCT 2019

The tongue-palate system is able to detect fine texture variations in the mouth where the best rheometers are essentially blind. One hypothesis to explain this remarkable sensitivity is the presence of myriads of filiform papillae on the surface of the tongue and mechanoreceptors at their base.

During this thesis, we developed a biomimetic approach reproducing the functioning of the oral cavity. The tongue is an elastomer block decorated with elongated cylinders assimilated to filiform papillae. It is placed on the bottom of the cell of a rheoscope, a combination of a rheometer and a microscope. The rotating rheometer tool plays the role of the rigid palate, and imposes the flow of the tested liquid.

We have imaged while shearing simple fluids the deflection of a papilla and showed that it is proportional to the viscous stresses, in perfect agreement with a recent elastohydrodynamics model. We probed the deflection of a papilla in the presence of granular suspensions as models of food emulsions. We have shown that the presence of particles in the continuous phase slightly modifies the average deformation of a papilla, but strongly changes the standard deviation around this deformation, mainly because of particle/papilla collisions. Finally, we studied the effect of papillae interactions by varying their surface density. This deflection decreases with density. A phenomenological model that treats the papillae as an effective porous medium successfully describes our data across the entire density range.