Elucidating Length and Time Scales of Spatiotemporal Heterogeneity in Supercooled Liquids

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In this project supported by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Professor Laura Kaufman, together with her postdoctoral associates, graduate students, and undergraduate researchers at Columbia University will investigate fundamental aspects of spatiotemporal heterogeneity in small molecule and simulated model supercooled liquids. The proposed experiments will employ a set of carefully chosen probe molecules that allow for systematic interrogation of the length and time scales of heterogeneity in a variety of small molecule glass formers. These measurements will detail the spatial and temporal extents of heterogeneity in particular supercooled liquids and may suggest underlying connections between supercooled liquid fragility and breadth of spatiotemporal heterogeneity. Beyond typical supercooled liquids, experiments on systems that display similar phenomenology but are suspected of possessing structural heterogeneity are proposed. In addition to these measurements that monitor single molecule (SM) probe rotational dynamics, experiments that directly interrogate translational diffusion at the SM level will be undertaken. Simultaneous tracking of rotations and translations will resolve questions regarding the poorly understood phenomenon of rotational-translational decoupling in supercooled liquids, revealing whether this behavior can exist on a single molecule level. Accompanying carefully crafted simulations will allow for both rotational and translational motility to be tracked in analogy with the proposed experiments and will investigate reciprocal probe-host interactions in a manner that will inform and strengthen interpretation of experimental results. Achieving a fuller understanding of spatiotemporal heterogeneity in supercooled liquids is of great fundamental interest as well as of applied interest in diverse fields, from petroleum transportation to cryopreservation of cells. The proposed work will also have strong educational impact on undergraduate, graduate, and postdoctoral researchers in the Kaufman laboratory as well as on younger students. Professor Kaufman has initiated a relationship with a local charter school to present lectures on complex fluids to 4th-6th grade students, collaboratively develop additional lectures with their science teacher, and translate real-time assessment tools used in this school into the General Chemistry courses at Columbia University. Through service on Columbia University's Quality of Life Committee, Professor Kaufman will facilitate dissemination of information to Columbia University science students and faculty on federal agency and University-based family friendly policies, and will assist in design, dissemination, and analysis of a study on Columbia University faculty use and perceptions of the University's family leave policies.