This award supports theoretical and computational research and education in granular and soft-matter materials. Granular and soft-matter materials are ubiquitous in nature and every day life. One such class of materials is dry granular materials, which includes powders, seeds, grains, sand, and gravel. Another class are classified among soft-matter materials, and generally consist of particles suspended in fluids. These include: emulsions consisting of droplets of one fluid suspended in a second fluid, such as mayonnaise, vinaigrettes, and homogenized milk; foams consisting of bubbles of gas suspended in a fluid, such as shaving cream, soap bubbles, and whipped cream; and suspensions consisting of solid particles suspended in a fluid, such as ketchup, mustard, and paint. These materials are important for a wide variety of technologies and industrial processes, from the processing of pharmaceuticals and foods, to transportation of seeds and grains, to materials fabrication.
At the simplest level of abstraction, one may think of these materials as consisting of large particles, for which thermal fluctuations are negligible, that interact only when they come into contact with each other, in which case they repel. Yet despite this seeming simplicity, surprisingly complex behavior may emerge, in particular a transition from a flowing liquid-like state to a rigid but disordered solid state, as either the particle packing density or applied stress is varied. This is known as the "jamming transition." In this project, computer simulations will be used to investigate the nature of this jamming transition, along with more general behavior of such materials that emerges under shear driven flow where adjacent granular layers move parallel to each other with different relative speed. Different mechanisms for energy dissipation, and the effects of different particle shapes will be investigated.
This project will also promote the teaching, training, and engagement in science and research, of a wide range of students across multiple institutions. Undergraduate students will gain experience in both scientific research and scientific communication by presenting work at local and national research conferences. Graduate students will be trained in the methods of modern theory and high-performance computing and experience research with direct interaction between theory and experiment. In this way, they become prepared for future high-tech careers in academia or industry. The infrastructure for research and education will be enhanced by the formation of a network of collaborations with domestic and international colleagues engaged in complementary experimental and computational research in this area.
This award supports theoretical and computational research and education in granular and soft-matter materials. Computer simulations will be carried out to study different aspects of the behavior of granular and soft-matter materials near the jamming transition that marks the abrupt change from a flowing liquid-like state to a rigid but disordered solid state, as the particle packing is increased. Materials of interest include dry granular matter, dense granular particles in a slurry, emulsions, foams, non-Brownian suspensions, and colloids. Specific problems will be investigated, with the objective of increasing understanding about the flowing liquid and disordered solid phases of such materials, and the transitions between them. These include: (i) the physical mechanisms behind shear banding of shear flowing materials in homogeneous environments; (ii) the relation between discontinuous shear thickening, the rapid jump in shear stress upon increasing the strain rate, and microscopic inter-particle elastic friction; (iii) the differences between isotropic compressional jamming and shear jamming, in systems of frictional particles; (iv) the effect of orientational ordering and particle tumbling on the shear flow of materials consisting of aspherical particles; (v) the criticality of the shear-driven jamming transition for aspherical particles; (vi) the effect of particle surface concavity on shearing rheology. Collaborations with experimental groups working in these areas will help inform and guide theoretical progress.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
