Statistical Physics of Systems of Grains, Fibres and Sheets

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

****NON-TECHNICAL ABSTRACT**** How do loose grains pack into a sand pile? How do long strands arrange into springy, elastic, fibrous matter? How is it that a flimsy piece of paper becomes rigid when crushed into a ball that is mostly empty space? This individual investigator award supports a project to develop techniques for imaging the interior of such structures with a view to understanding the architecture that leads to the mechanical properties that define each of these classes of materials. Model laboratory systems will be used to enable our understanding of the behavior of their more complex counterparts in the physical, technological and biological world. The intellectual challenge in understanding these systems is that unlike conventional phases of matter these so-called nonequilibrium systems are defined not just by their present state but by the history to which they have been subjected. Undergraduates from UMass and other colleges in the area will lead exploratory work on new projects while graduate students will work on more long-term projects using techniques that include a battery of modern experimental tools. All students will be exposed to research questions of fundamental importance in nonequilibrium statistical physics in the context of everyday materials. ****TECHNICAL ABSTRACT**** The focus of this individual investigator award is the understanding of the structure, response, and stability of systems in which the constituent elements are macroscopic grains, fibres, or elastic sheets. The project seeks to identify general principles governing phase behaviour, fluctuations, bulk response and structure of such far-from-equilibrium systems. An experimental determination of packing and spatial configuration of model systems in each of these classes is indispensable in developing an understanding of their counterparts in the physical, technological and biological world. These systems are nonthermal, and their structure is a consequence of not just their constituents and their interactions but also their history of preparation. In the cases of fibres and sheets, the deformability of these elastic elements raises interesting geometrical issues. These issues are compounded by the material challenges of long-term plastic flow and of hysteretic frictional interactions. Undergraduates from UMass and other colleges in the area will lead exploratory work on new projects while graduate students will work on more long-term projects using techniques that include high-speed video imaging, confocal microscopy, light scattering, acoustic and mechanical response techniques, and x-ray tomography.