This proposal concerns the rheology and kinematics of suspensions (solid particles dispersed in a fluid) and dry granular materials. These materials are ubiquitous in nature and industrial processes. In suspensions, our interest is in Stokesian suspensions, wherein the Reynolds number based on particle size is small enough that particle and fluid inertia play no role. Familiar examples are aerosols, food and cosmetic emulsions, paints, and inks. When the interstitial fluid is a gas, the material is said to be dry; in such systems, when the particles are larger than 100 microns, the effect of the gas is often unimportant. We refer to such systems simply as granular materials, in keeping with the literature, familiar examples of which are food grains, mineral ores, and sand. In granular materials too, our interest is in the “slow flow” regime. In non-colloidal Stokesian suspensions, it is conventionally assumed that inter-particle interactions are determined solely by the fluid, as the lubrication forces grow strongly with decreasing inter-particle separation to prevent direct contact. In dry granular materials, on the other hand, particle contact plays a dominant role in determining the stress. One of the principal objectives of this proposal is to bridge the descriptions between the fluid-dominated Stokesian suspension and the contact-dominated granular medium. Experimental evidence indicates that particle contact may play a significant role in the rheology of suspensions when the volume fraction of particles is high. We aim to quantify by rheological measurements and particle dynamics simulations the extent to which contact plays a role. Experimentally we propose to address this problem by using particles whose surface properties are altered, by (i) coating them with a soft, deformable layer, and (ii) by roughening the surface. The related theoretical objective is to evolve a rheological description that bridges Stokesian suspensions with dry granular materials by (i) identifying the important dimensionless parameters that characterize the effect of fluid viscosity, particle contact, and particle and fluid inertia, and (ii) obtain a relation for the stress tensor as a function of these parameters and the field variables. Our other objectives are to attempt to answer some open questions are: what are the normal stress differences in dry granular materials and dense suspensions?; how does the rheology depend on the surface properties of the grains; how do microstructural features (such as the fabric) vary between dense suspensions and dry granular materials?. Answers to these questions will lead to a fundamental understanding of the rheology of particulate materials, and thereby formulation of more accurate constitutive models. Our approach will be to use the unconventional rheological tools that we have developed in Marseille and Bangalore and examine how the macroscopic rheology (in particular the divergence close to the jamming transition and the occurrence of normal stress differences) is influenced by the nature of the contact between the particles and in particular surface roughness and friction as well as softness and deformability. Our first objective is to manufacture spherical particles having controlled surface properties. Once these specific particles are produced, they will be used in rheological measurements using the rheological tools developed in both groups (pressure-imposed rheometry, profilometry for measurements of normal stresses, and Couette device). These experiments will be complemented by numerical simulations (Stokesian Dynamics simulations for suspensions and Discrete Element Method simulations for granular flows that are expected to converge as the particle fraction nears the value at jamming).