研究领域

Physical Chemistry

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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K. Stokely, A.S. Manz, and L.J. Kaufman. "Revealing and resolving degeneracies in stretching exponents in temporally heterogeneous environments," J. Chem. Phys. Accepted. K. Paeng, H. Park, D.T. Hoang, and L.J. Kaufman. "Direct demonstration of ergodicity in a supercooled liquid via ideal probe single molecule experiments," Proc. Nat. Acad. Sci. Accepted. H. Park*, D.T. Hoang*, K. Paeng, and L.J. Kaufman. "Localizing exciton recombination sites in conformationally distinct single conjugated polymers by super-resolution fluorescence imaging," ACS Nano. In Press. Published online ahead of print D.T. Hoang, K. Paeng, H. Park, L.M. Leone, and L.J. Kaufman. "Extraction of Rotational Correlation Times from Noisy Single Molecule Fluorescence Trajectories," Anal. Chem. 86, 9322-9329 (2014). PDF A. Guzman, M.J. Ziperstein, and L.J. Kaufman. "The effect of fibrillar matrix architecture on tumor cell invasion of physically challenging environments," Biomaterials. 35, 6954-6963 (2014). PDF Supplementary Information J. Zhu and L.J. Kaufman. "Collagen I self-assembly: Revealing the developing structures that generate turbidity," Biophys. J. 106, 1822-1831 (2014). PDF Supplementary Information Supporting Movie 1 Supporting Movie 2 K. Paeng and L.J. Kaufman. "Single molecule rotational probing of supercooled liquids," Chem. Soc. Rev. 43, 977-989 (2014). PDF L.M. Leone and L.J. Kaufman. "Single molecule probe reports of dynamic heterogeneity in supercooled ortho-terphenyl," J. Chem. Phys. 138, 12A524 (2013). PDF L.J. Kaufman. "Heterogeneity in single molecule observables in the study of supercooled liquids," Ann. Rev. Phys. Chem. 64, 177-200 (2013). PDF S. Motte and L.J. Kaufman. "Strain stiffening in collagen I networks," Biopolymers 99, 35-46 (2013). PDF Supplementary Information S.A. Mackowiak, J.M. Noble, and L.J. Kaufman. "Manifestations of probe presence on probe dynamics in supercooled liquids," J. Chem. Phys. 135, 214503 (2011). PDF Y. Yang, C. Sun, M.E. Wilhelm, L.J. Fox, J. Zhu, and L.J. Kaufman. "Influence of chondroitin sulfate and hyaluronic acid on structure, mechanical properties, and glioma invasion of collagen I gels," Biomaterials 32, 7932-7940 (2011). PDF S.A. Mackowiak and L.J. Kaufman. "When the heterogeneous appears homogeneous: Discrepant measures of heterogeneity in single molecule observables," J. Phys. Chem. Lett. 2, 438-442 (2011). PDF S.A. Mackowiak, L.M. Leone, and L.J. Kaufman. "Probe dependence of spatially heterogeneous dynamics in supercooled glycerol as revealed by single molecule microscopy," Phys Chem Chem Phys 13, 1786-1799 (2011). PDF Supplementary Information Y. Yang, S. Motte, and L.J. Kaufman. "Pore size variable collagen gels and their interaction with glioma cells," Biomaterials 31, 5678-5688 (2010). PDF S.S. Gallagher, C. Jing, D.S. Peterka, M. Konate, R. Wombacher, L.J. Kaufman, R. Yuste, and V.W. Cornish. "A trimethoprim-based chemical tag for live cell two-photon imaging," ChemBioChem. 11, 782-784 (2010). PDF J.C. Conrad, H.M. Wyss, V. Trappe, S. Manley, K. Miyazaki, L.J. Kaufman, A.B. Schofield, D.R. Reichman, and D.A. Weitz. "Arrested fluid-fluid phase separation in depletion systems: Implications of the characteristic length on gel formation and rheology," J. Rheol. 54, 421-438 (2010). PDF Z. An, C.B. Gluck, M.L. Choy, and L.J. Kaufman. "Suberoylanilide hydroxamic acid limits migration and invasion of glioma cells in vitro," Cancer Lett. 292, 215-227 (2010). PDF S.A. Mackowiak*, T.K. Herman*, and L.J. Kaufman. "Spatial and temporal heterogeneity in supercooled glycerol: Evidence from wide field single molecule imaging," J. Chem. Phys. 131, 244513 (2009). PDF Y. Yang, L.M. Leone, and L.J. Kaufman. "Elastic moduli of collagen gels can be predicted from two dimensional confocal microscopy," Biophys. J. 97, 2051-2060 (2009). PDF J.Y. Lee, B.H. Hong, W.Y. Kim, S.K. Min, Y. Kim, M.V. Jouravlev, R. Bose, K.S. Kim, I.-C. Hwang, L.J. Kaufman, C.W. Wong, P. Kim, and K.S. Kim. "Near-field focusing and magnification through self-assembled nanoscale spherical lenses," Nature 460, 498 - 501 (2009). PDF Z. An, K. Kavanoor, M.L. Choy, and L.J. Kaufman. "Polyelectrolyte microcapsule interactions with cells in two and three dimensional culture," Coll. Surf. B: Biointerfaces 70, 114-123 (2009). PDF Y. Yang and L.J. Kaufman. "Rheology and confocal reflectance microscopy as probes of structure and mechanical properties during collagen and collagen/hyaluronan self assembly," Biophys. J. 96, 1566-1585 (2009). PDF T.K. Herman, S.A. Mackowiak, and L.J. Kaufman. "High power light emitting diode based set-up for photobleaching fluorescent impurities," Rev. Sci. Inst. 80, 016107 (2009). PDF B.M. Rubenstein and L.J. Kaufman. "The role of extracellular matrix in glioma invasion: A cellular Potts model approach," Biophys. J. 95, 5661-5680 (2008). PDF R. Chatterjee, N.C. Panoiu, K. Liu, Z. Dios, M.B. Yu, M.T. Doan, L.J. Kaufman, R.M. Osgood, and C.W. Wong. "Achieving subdiffraction imaging through bound surface states in negative refraction photonic crystals in the near-infrared range," Phys. Rev. Lett. 100, 187401 (2008). PDF