Jamming and Glassy Behavior in Systems with Nonspherical Particles and Constrained by Chain Connectivity

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TECHNICAL SUMMARYThis award supports theoretical and computational research and education on jamming transitions. Jamming transitions, in which systems transform from liquid-like to solid-like states, have been studied intensely in many systems, including granular media, foams, and colloids. However, a significant limitation of prior studies is that they have been confined largely to idealized systems composed of spherical particles. Yet, there are a host of physical systems that undergo glass and jamming transitions with more complex microstructures. For example, most granular systems and colloidal and molecular liquids are composed of non-spherical particles. Recent developments in colloidal synthesis and self-assembly now allow the efficient production of large quantities of anisotropic particles. Many systems that form glasses are polymeric, and the constraint of chain connectivity plays an important role in determining their structural and mechanical properties. The PI will perform extensive theoretical and computational studies with the aim of extending jamming research in two new directions: (1) studies to explore how jamming and glassy behavior depends on particle shape and (2) studies to understand how the constraint of chain connectivity affects the packing of collapsed polymers and model proteins.These studies aim toward a deeper understanding of soft matter systems that undergo jamming and glass transitions. They will have a potentially transformative impact on the research communities that study polymer collapse and protein folding through the application of the tools and concepts developed in jamming studies to these areas. This project will benefit from collaborations with experimentalists who will help to directly compare theory, simulations, and experiments. The efforts of collaborators include fabrication of dimers and trimers of fused polystyrene spheres and visualizing them using optical and SEM imaging techniques; characterization of dense suspensions of boehmite, which are nm-sized rod-like particles using x-ray scattering; and the study of collections of colloidal particle clusters generated using depletion interactions. The work on polymer collapse will also benefit from direct collaboration with experiment to study the packing of hydrophobic residues and its affect on kinetics using coarse-grained heteropolymer models.This research project is conducive to training graduate and undergraduate students. The PI will design modules on statistical mechanics, molecular simulations, and glass transitions that will be integrated into the curriculum of an interdisciplinary program at Yale. The PI will recruit highly talented minority undergraduate students through the Science, Technology and Research Scholars, Summer Undergraduate Research Fellowship, and Raymond and Beverly Sackler Institute fellowship programs at Yale. The PI will mentor at least one student from one of these programs each summer of the grant period. The PI is the director of the Sackler Institute Undergraduate Fellowship Program, which partners with HBCU Claflin University. In the first year of the grant, the PI will attend graduate recruiting fairs such as the Big Ten Plus Graduate Expo to recruit talented Ph.D. applicants, especially those from underrepresented groups. NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education on jamming transformations. Jamming is a ubiquitous phenomenon wherein materials transform from liquid-like to amorphous solid-like states. Examples in soft matter include clogging of hoppers, channels, and pipes that convey particulate media and dispersions. Disruptions of the transport and processing of particulate systems waste enormous amounts of energy and economic resources in the pharmaceutical, oil, and food industries. A quantitative and predictive understanding of jamming transitions may lead to more efficient technologies that eliminate unwanted jamming behavior and increase the ability of many granular materials to remain in a flowing state.A significant limitation of previous theoretical and computational studies of jamming is that they have been mostly confined to idealized particulate systems. For example, most granular systems, such as sand and powders, and colloidal and molecular liquids and glasses, are composed of particles that are not ideal spheres. Moreover, recent developments in self-assembly now allow the efficient production of large quantities of particles that are distinctly different from spheres. Many systems that jam and form glasses are composed of long chain-like molecules, polymers, and the constraints this brings plays an important role in determining the structural and mechanical properties of these materials.The PI will conduct extensive theoretical and computational studies that will direct research on jamming in two exciting, new directions: (1) studies to explore how jamming and glassy behavior depend on particle shape and (2) studies to understand how the constraint of chain connectivity affects the packing and dynamics of collapsed polymers. Polymers can undergo a transformation or collapse where the long molecule chains are in an open coil like structure which gives way at the transition to a more compact ball-like structure. This research project is conducive to training graduate and undergraduate students. The PI will design modules on statistical mechanics, molecular simulations, and glass transitions that will be integrated into the curriculum of an interdisciplinary program at Yale. The PI will recruit highly talented minority undergraduate students through the Science, Technology and Research Scholars, Summer Undergraduate Research Fellowship, and Raymond and Beverly Sackler Institute fellowship programs at Yale. The PI will mentor at least one student from one of these programs each summer of the grant period. The PI is the director of the Sackler Institute Undergraduate Fellowship Program, which partners with HBCU Claflin University. In the first year of the grant, the PI will attend graduate recruiting fairs such as the Big Ten Plus Graduate Expo to recruit talented Ph.D. applicants, especially those from underrepresented groups.