Rheophysics of concentrated particle suspensions in a Couette cell using a refractive index matching technique

The main objective of this work is to gain insight into the rheometry and rheology of concentrated non-colloidal particle suspensions. Among the many questions that have as yet received little answers, we are especially interested in the rheometric problems associated with this type of fluid and in their rheology in the frictional and viscous regimes, as well as the transition between both regimes —a topic that is particularly unclear. To address these issues, we had initially to develop techniques capable of measuring non-invasively the velocity field within these concentrated suspensions. Part of this thesis is dedicated to the development and implementation of an optical visualization technique inside concentrated suspensions, which was developed at the Laboratory of Environmental Hydraulics. This measurement technique combines the development of iso-index fluids and the use of fluorescent particle image velocimetry. On this basis, we could then tackle the real issues of this work, that is, on the one hand, rheometric measurement techniques of these fluids and, on the other hand, the rheologic properties. Among the issues discussed, the following were the main: Is it possible to obtain a reliable flow curve for concentrated particle suspensions from bulk measurement? And this by considering the wide shear range within the gap, the non-homogeneous material and the inversion-technique problems due to the wide gap? What are the main rheological properties of concentrated non-colloidal particle suspensions in the frictional and viscous regimes? What about the transition between these two regimes?