Shearing Rheology and Glassy Behavior in Athermal and Thermalized Models of Granular Materials, Simple Liquids, and Amorphous Solids

University Of Rochester, Rochester NY

Investigators

Abstract

TECHNICAL SUMMARY This award supports theoretical research and education on the nature of equilibrium and driven nonequilibrium critical phenomena in granular materials, glassy forming simple liquids, and related soft matter systems such as foams, emulsions and colloids. Using extensive numerical simulations, the PI will investigate new regions of the jamming phase diagram that characterize a diverse array of physical systems that undergo transitions from flowing liquid-like states to rigid but structurally disordered states. The research will focus on the following activities: (i) The PI will study the rheology of athermal amorphous solids above jamming, characterizing the singular behavior as one approaches the yield stress, and exploring the relation to dynamic heterogeneity. (ii) The PI will investigate the relationship between thermal glassy behavior and the athermal jamming transition. Shear driven steady states at low temperature and low shear strain rate will be used as a new probe to demonstrate whether a true singular thermal glass transition exists. (iii) The PI will explore the effect of different dynamics on the critical behaviors of interest, in particular the difference between mean-field and non-mean-field models of viscous dissipation, and the crossover from inertial to overdamped dynamics. (iv) The PI will study the effect of frictional forces on shear driven athermal jamming. The experimental observation of novel shear jammed states will be explored in simulations. The PI will examine the effect differing models for friction, sliding contacts as opposed to geometric asperities, have on simulation phenomena. These investigations will also address the applicability of concepts and methods from equilibrium statistical mechanics to fundamentally nonequilibrium systems and driven steady states. Undergraduate students will participate in the research, gaining experience, skill, and insight into modern scientific research and methods of numerical simulation. The University of Rochester has several site REU programs that greatly assist in attracting high quality undergraduate students to work on summer research projects. Many of these continue with senior projects or theses during the following year. This project involves international collaboration with Ume¢ªa University in Sweden, as well as other research groups at Duke, Yale, and Rochester. These interactions will provide students with the opportunity to directly confront theory with experiment, to use state of the art high performance computing platforms. NON-TECHNICAL SUMMARY This award supports theoretical research and education on granular and glassy materials with an emphasis to investigate the nature of the apparent transitions from a flowing liquid-like state to a rigid state with an amorphous structure that occur in granular materials, foams, colloids, emulsions, and liquids cooled to become a glass. The understanding of granular and glassy materials is not only of intrinsic scientific interest, but is important for a wide variety of industrial processes, from the processing of pharmaceuticals, to transportation of seeds and grains, to materials fabrication. This research will contribute to the knowledge base on granular and glassy materials and may lead to advances and improvements in efficiency in many important areas of modern industry and technology. Using extensive numerical simulations, the PI will explore uncharted regions of the jamming phase diagram, a diagram that charts the conditions under which materials undergo transitions from flowing liquid-like states to rigid but structurally disordered states. The jamming transition occurs far from the steady state of equilibrium. While the theory of nonequilibrium statistical mechanics is not well developed, an important research direction is to investigate the extent to which the concepts and methods of equilibrium statistical mechanics can be applied or adapted to the realm of nonequilibrium systems and driven steady states. The PI will contribute to this effort. The PI will explore the relationship between the jamming transition and the transition where a cooling liquid becomes a glass. Because the energy scales in granular systems are usually very high compared to the temperature, temperature does not normally play a role in the jamming transition. The PI will use a novel strategy and innovative techniques to study the nature of the jamming transition at sufficiently high temperatures and compare the signatures of the jamming transition at temperature to the glass transition. Studies of granular systems often neglect friction between particles, but nonetheless are able to observe the jamming transition. The PI plans to study the effect of frictional forces that occur in real granular materials on jamming. The PI will investigate different models through simulation to illuminate experimental observations of novel jammed states that occur under the application of shear strain. Undergraduate students will participate in the research, gaining experience, skill, and insight into modern scientific research and methods of numerical simulation. The University of Rochester has several site REU programs that greatly assist in attracting high quality undergraduate students to work on summer research projects. Many of these continue with senior projects or theses during the following year. This project involves international collaboration with Ume¢ªa University in Sweden, as well as other research groups at Duke, Yale, and Rochester. These interactions will provide students with the opportunity to directly confront theory with experiment, to use state of the art high performance computing platforms.