Concentrated suspensions: towards denser and less viscous materials – FLUIDIDENSE

Carbon black particles are the most widely used nanoparticles in rubber to reinforce tires. Their production contributes much to air pollution and to the greenhouse effect. The introduction of silica particles in tires, to replace partially carbon black particles, is therefore a major ecological advance. While significantly reducing the environmental footprint of tires, these particles have reduced the tires rolling resistance, leading to a reduction in fuel consumption and CO2 emissions of up to 5%. Production of precipitated silica for "green tires", however, remains a major source of water and energy wastage. Indeed, to date, the process requires to handle moderately concentrated suspensions of silica particles, with a viscous fluid behavior that is quite simple, the water of which must ultimately be dried. A substantial ecological progress would therefore result from the possibility of handling more concentrated but still fluid suspensions.

The objective of the FLUIDIDENSE project is to make major advances in the description and the understanding of the behavior of concentrated suspensions, the flows of which tends to jam and to be inhomogeneous, and to provide new paths for the formulation of concentrated suspensions that can be handled. In this wide field of research, it is crucial to focus on a material whose surface physicochemistry is controlled, and to study in depth all the aspects of its behavior, in relation to the interparticle interactions that has to be characterized explicitly. In view of the application, we will focus the study on suspensions of amorphous silica particles, which will be synthesized by varying their shape, their degree of aggregation, and their surface properties. The originality and the strength of the proposed approach are that it relies on a study of the same systems using a set of advanced techniques to locally characterize the flows of silica suspensions (velocity profiles by ultrasonic velocimetry, structure/properties relationship by rheo-SAXS, development of concentration inhomogeneities by X-ray radiography) and their morphological properties (SAXS, MEB), as well as their microscopic properties (original measurements of normal and tangential interparticle forces in the suspending fluid). For all the studied particles, a multi-scale characterization of the behavior will be available, the synthetic vision of which will provide a clarification of the conditions under which dense, fluid and homogeneous suspensions can be formulated.

The in-depth characterization of the behavior of silica suspensions will make it possible to propose ways of modifying the process to the industrial partner. Understanding the link between their behavior and the physicochemical properties of the particles will provide realistic levers for formulating suspensions that are denser though still fluid. This project will contribute to the transition towards a "green plant" through energy and water savings and through the reduction of air pollution that will result from process improvements and from anticipated reductions in the use of carbon black particles.