Objective: This project aimed to advance the fundamental understanding of powder flows by developing model cohesive granular materials and characterizing their rheological behavior to improve powder manipulation in industrial processes. The primary focus was to tune adhesive forces, develop original experimental setups to characterize particle interactions, and design a shear cell capable of investigating inertial rheology at low pressure. The ultimate goal was to provide physical insights into flowability, with applications in processes such as aeration, compaction, and industrial handling.
Key Achievements:
• Development of Model Materials: Successfully created model cohesive particles with tunable adhesion, using polymer coated silica and functionalized polymer particles. Demonstrated the ability to control adhesive properties, enabling systematic studies of cohesion effects.
• Characterization of Particle Properties: Developed experimental techniques to measure interparticle adhesion and friction. Identified a lubrication transition in large particles, characterized through tribological measurements at the particle scale.
• Bulk Rheology Measurements: Designed and implemented a novel shear cell capable of measuring the rheology of _ne particles under low confinement stresses and in the inertial regime. Achieved the first measurements of constitutive laws under low confining stress, revealing unexpected behaviors such as shear weakening and pressure-dependent transitions.
• Study of Flow Configurations: Initiated investigations into ow configurations relevant to industrial processes, including compaction and drag/lift forces in cohesive materials. Observed that lift forces are signficantly more sensitive to cohesion than drag forces, suggesting potential new methods for powder characterization.
Challenges and Limitations:
The study of air-particle coupling, a critical aspect of powder dynamics, was not addressed due to time constraints and the complexity of designing appropriate experimental tools. Some objectives, such as the systematic study of ow configurations, remain preliminary and require further investigation.
Impact and Future Directions:
This project has laid the groundwork for a deeper understanding of cohesive granular flows, with implications for industrial processes involving powders. The development of model materials and advanced experimental techniques opens new avenues for studying the interplay between adhesion, friction, and ow dynamics. Future work will focus on refining measurements to reveal the control parameters of the powder rheology, and extending findings to a broader range of industrial applications.
Conclusion:
This project has made signficant progress in developing innovative tools to characterize cohesive granular materials, both at the particle scale and in terms of bulk properties. We have begun to gain valuable insights into the behavior of powders under low confinement and inertial conditions. While challenges remain, particularly in fully understanding the role of air-particle interactions and refining ow configurations, the findings provide a robust foundation for future research, with direct relevance to the industrial characterization and handling of powders.