Bio in Brief
We endeavor to understand the structure, dynamics, and mechanical properties of systems that are variously (and loosely) described as crowded, frustrated, or jammed. In these systems, the particles of interest, whether they be as small as molecules (on the order of 10-10 m) or as large as cells (on the order of 10-5 m), are frustrated in their rotational and/or translational motion due to details of the structural, dynamical, and/or mechanical properties of their surroundings. Systems displaying frustrated dynamics include both molecular and colloidal supercooled liquids and glasses, as well as biological systems (the motion of macromolecules in biopolymer networks, as well as the motion of cells in tissue, demonstrates aspects of frustrated dynamics). In molecular and colloidal glassy systems, we wish to study fundamental issues concerning jammed dynamics, such as whether there are structural manifestations of the dramatic dynamical slowdown that occurs around a glass transition. In the biological systems we address, we ask more practical questions, such as how confinement in cells and tissues influences cell mobility and growth.

Because the length and time scales over which these frustrated dynamics take place differ substantially between molecular and colloidal and biological systems, we employ a wide range of spectroscopic and microscopic techniques together with theoretical modeling to probe and understand these systems. We use single-molecule-spectroscopy to elucidate the behavior of individual molecules in glassy molecular systems, while we use laser scanning microscopy together with particle tracking techniques to study similar behaviors in colloidal glassy systems. Nonlinear microscopies and one-photon fluorescent microscopy are used in concert with microrheological techniques to elucidate these dynamics in biological systems. The techniques we employ have one principal similarity: they are not ensemble measurements that average over different local environments in the systems. Instead, these techniques probe these different local environments, or spatial heterogeneities, in detail to elucidate if and how they cause (or result from!) the jammed or frustrated dynamics in these systems. To further study spatial and dynamical heterogeneities in such systems, we also develop new spatio-temporally resolved techniques that are analogous to time-resolved spectroscopic techniques, but are performed on much smaller focal volumes (mm3), and thus are ideal for colloidal and biological systems, which are heterogeneous on that length scale.

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Publications

Towards Elucidating the Role of the Probe in Single Molecule Experiments in Supercooled Liquids,  R. Zangi, S.A. Mackowiak, T. Herman, K. Kavanoor, and L.J. Kaufman, Proceedings of the Fourth International Workshop on Complex Systems, In press

Frequency-dependent Stokes-Einstein Relation in Supercooled Liquids, R. Zangi and L.J. Kaufman,  Phys. Rev. E 75, 105501 (2007)

Probe Particles Alter Dynamic Heterogeneities in Simple Supercooled Systems, R. Zangi, S.A. Mackowiak, and L.J. Kaufman. J. Chem. Phys. 126, 104501 (2007)

Flow and Magnetic Field Induced Collagen Alignment, C. Guo and L.J. Kaufman, Biomaterials 28, 1105-1114 (2007)

Direct Imaging of Attractive and Repulsive Colloidal Glasses, L.J. Kaufman and D.A. Weitz,  J. Chem. Phys. 125, 074716 (2006)

Glasslike Arrest in Spinodal Decomposition as a Route to Colloidal Gelation, S. Manley, H. Wyss, K. Miyazaki, J.C. Conrad, L.J. Kaufman, D.R. Reichman, and D.A. Weitz,  Phys. Rev. Lett. 95, 238302 (2005)

Glioma Expansion in Collagen I Matrices: Analyzing Collagen Concentration-Dependent Growth and Motility Patterns, L.J. Kaufman, C.P. Brangwynne, K.E. Kasza, E. Filippidi, V.D. Gordon, T.S. Deisboeck, and D.A. Weitz, Biophys. J. 89, 635-650 (2005)  

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