Matthieu Wyart - US grants

TECHNICAL SUMMARY

The Division of Materials Research contributes funds to this award. It supports theoretical and computational research and education on soft condensed matter and non-equilibrium statistical mechanics at the interface of materials research and mathematics. The research includes the study of the flow of particulate fluids, such as granular matter, emulsions or suspensions, in the vicinity of the jamming transition where these materials solidify. In various ways, the research contributes to the advance of non-equilibrium statistical mechanics, and to the rheology of complex fluids.

The PI aims to use methods from theoretical physics to understand dense flows of particulate fluids. The rheology and the effects of confinement on flow properties near jamming have been studied experimentally in a variety of materials. It emerges that these fluids display a critical behavior at the jamming transition where the dynamics stops: the motion of the particles becomes more and more collective as the transition is approached, and the constitutive relations relating stress, strain rate and packing fraction scale with distance to threshold. The PI plans to study such phenomena through a combination of techniques from non-equilibrium statistical mechanics, probability theory, and geometry, with particular emphasis understanding the spatial nature of the 'soft modes' - the collective allowed motions of the particles- and their coupling to the flow. The PI plans in particular to construct a detailed theory of the relationship between the geometry of particle clusters generated in flows, their convection and break-up, and the soft modes characterizing them. Numerical simulations will be used to quantify these relationships, and to test for the applicability of concepts that have recently enhanced understanding of isotropic jammed materials, in particular the idea of marginal stability.


This award also supports interdisciplinary training for graduate students and post-docs through the opportunities provided by the research.

NONTECHNICAL SUMMARY:

The Division of Materials Research contributes funds to this award. It supports theoretical and numerical research and education on soft condensed matter and non-equilibrium statistical mechanics at the interface of materials research and mathematics. The research includes the study of the flow of particulate fluids, such as granular matter, emulsions, or suspensions, in the vicinity of the jamming transition where these flowing materials become rigid. For example food grains in a silo can flow easily through hoppers or the flowing grain becomes rigid and abruptly stops. In various ways, the research contributes to the advance of non-equilibrium statistical mechanics - the study of systems of many particles or components that are far from balance, and to the rheology of complex fluids.

The PI aims to use methods from theoretical physics to understand dense flows of particulate fluids. Particulate fluids, such as granular materials, are the most commonly processed materials in industry after water. Controlling the rheology of these materials is of considerable interest including in the cosmetic, energy, food and pharmaceutical industries. Potential applications of the funded research include controlling the fluidization of particulate fluids to lower the cost of their processing and transport. Fluidization is crucial for example for the extraction and transport of oil sands, that represent two thirds of liquid hydrocarbon resources but that are very costly to process. A better understanding of how particulate fluids flow contributes to efforts to make these resources available.


This research contributes to the intellectual foundations of the discovery of new materials, new technologies through a better understanding of the fundamental microscopic principles that governs them.

This award also supports interdisciplinary training for graduate students and post-docs through the opportunities provided by the research.

1236378
PI: Wyart

Particulate materials, such as suspensions or granular matter, are the most commonly used materials in industry after water. However, explaining their rheological properties remains a challenge. These systems are complicated by the presence of disorder as well as by structural and dynamical heterogeneities, often on multiple length scales. At high densities, such a granular fluid undergoes a jamming or glass transition where the dynamics stop. In recent years there has been a considerable effort to characterize this transition, and it has been realized that dynamical heterogeneities play a key role. However, there is no consensus concerning what causes such heterogeneities. This project will develop a novel method to measure the micro-scale elasticity of amorphous materials. This approach will be used both experimentally and numerically to characterize the disorder and heterogeneities of amorphous solids, and to investigate the jamming transition by which they are formed. The method consists of introducing probe particles of controlled shapes and sizes. Thermal noise causes the probe particles to rotate on a time scale governed by the elasticity of their local environment, and by their shape and size. Measuring the rotational dynamics of the probe by means of confocal microscopy, light scattering, or numerically in simulations will give access to local elastic properties. The range of time scales and length scales can be tuned by controlling the shape and size of the probes. This method will be employed in colloidal suspensions, both experimentally and numerically, to measure the evolution of elasticity and its spatial heterogeneities as the concentration of colloids is increased, and to test fundamental theories of the glass transition.

This project will create an experimental method to probe the microscopic properties of disordered granular materials, the most commonly used materials in industry after water. This method will address questions of fundamental and practical importance in the fields of particle flow, biophysics, soil mechanics, and material science. Insights gained from this study will help improve the design of glassy materials and advance our understanding of clogging or jamming, which are of important for multi-phase flows relevant to the oil industry and potentially for the lethal vaso-occlusive eventt?clogging?occurring in sickle cell disease. In addition to these applications, the subject matter of this project lends itself to educational and community outreach activities.