NIRT: Complex Fluids Confined at the Nanoscale

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This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 03-043, category NIRT. This theoretical award is supported by the Division of Materials Research and the Chemistry Division. Fluids under extreme confinement exhibit novel dynamical properties which are not simple extensions of the bulk behavior. Intuitively, extreme confinement sets in when the confining dimensions become comparable to the length scales associated with the cooperative motion in the fluids which are typically in the nanometer domain. Understanding the interplay between these natural length scales and the external constraints is the goal of the research outlined in this grant. Constraints can be imposed by the external geometry such as in thin polymer films or liquids in porous media, but can also arise from "crowding" due to other objects as occur naturally in the interior of cells or in supercooled liquids near the glass transition. In all of these systems, temporal evolution involves the motion of extended objects which have internal degrees of freedom. Effective models at the scale of these objects will be constructed; a scale intermediate between the microscopic one characteristic of molecular dynamics simulations and the macroscopic scale of hydrodynamic descriptions. Such a framework provides a useful interface between theory and experiments which use real-space probes to study motion at the nanometer scale. In conjunction with such experiments, a framework relating length scales and time scales will be constructed and used to understand the effects of constraints on the dynamics. Numerical simulations will be used as a stepping stone in the construction of effective dynamical theories. The techniques will be developed in the context of lattice models and then extended to continuum models.The research will provide modeling tools for a range of problems in biology that includes rheology of cells, motion of macromolecules in crowded cell environments, dynamics of the cytoskeleton, to mention a few. On the technological side of things, much effort is currently being expended on miniaturizing and integrating various biochemical techniques for purifying, detecting, and sorting biological molecules, on a single chip. These techniques put front and center one of the central questions addressed by this research: How is the motion of macromolecules affected by extreme confinement? Theoretical tools such as simple models and numerical simulations, combined with experimentation on well controlled systems will contribute to the rational design of these "lab on a chip" technologies.A crucial aspect of the activities is building a community of physicists, chemists and biologists in the Boston area, united by their interest in dynamics of constrained systems. The managing PI has initiated a biannual meeting that brings together students, postdoctoral associates and faculty, in the Boston area, interested in glassy phenomena, broadly construed. These have proven invaluable for exchanging ideas between various groups and exposing students to a range of ideas. The current program builds on this activity by (i) describing a new summer research program aimed at undergraduates from the women's four-year colleges in the Boston area and (ii) enlarging the scope of the biannual meetings to include minicourses which will be a valuable addition to graduate education in the interdisciplinary area of slow dynamics.%%%This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 03-043, category NIRT. This theoretical award is supported by the Division of Materials Research and the Chemistry Division. Fluids under extreme confinement exhibit novel dynamical properties which are not simple extensions of the bulk behavior. Intuitively, extreme confinement sets in when the confining dimensions become comparable to the length scales associated with the cooperative motion in the fluids which are typically in the nanometer domain. Understanding the interplay between these natural length scales and the external constraints is the goal of the research outlined in this grant. Constraints can be imposed by the external geometry such as in thin polymer films or liquids in porous media, but can also arise from "crowding" due to other objects as occur naturally in the interior of cells or in supercooled liquids near the glass transition. In all of these systems, temporal evolution involves the motion of extended objects which have internal degrees of freedom. Effective models at the scale of these objects will be constructed; a scale intermediate between the microscopic one characteristic of molecular dynamics simulations and the macroscopic scale of hydrodynamic descriptions. Such a framework provides a useful interface between theory and experiments which use real-space probes to study motion at the nanometer scale. In conjunction with such experiments, a framework relating length scales and time scales will be constructed and used to understand the effects of constraints on the dynamics. Numerical simulations will be used as a stepping stone in the construction of effective dynamical theories. The techniques will be developed in the context of lattice models and then extended to continuum models.The research will provide modeling tools for a range of problems in biology that includes rheology of cells, motion of macromolecules in crowded cell environments, dynamics of the cytoskeleton, to mention a few. On the technological side of things, much effort is currently being expended on miniaturizing and integrating various biochemical techniques for purifying, detecting, and sorting biological molecules, on a single chip. These techniques put front and center one of the central questions addressed by this research: How is the motion of macromolecules affected by extreme confinement? Theoretical tools such as simple models and numerical simulations, combined with experimentation on well controlled systems will contribute to the rational design of these "lab on a chip" technologies.A crucial aspect of the activities is building a community of physicists, chemists and biologists in the Boston area, united by their interest in dynamics of constrained systems. The managing PI has initiated a biannual meeting that brings together students, postdoctoral associates and faculty, in the Boston area, interested in glassy phenomena, broadly construed. These have proven invaluable for exchanging ideas between various groups and exposing students to a range of ideas. The current program builds on this activity by (i) describing a new summer research program aimed at undergraduates from the women's four-year colleges in the Boston area and (ii) enlarging the scope of the biannual meetings to include minicourses which will be a valuable addition to graduate education in the interdisciplinary area of slow dynamics.***