Ph.D., Cornell University (1989) B.A., University of California, Berkeley (1984)

Chemical Physics and Physical Chemistry/Theory Simulation and Modeling

In my research group, we use a combination of analytical theory and numerical simulation to study problems in soft matter physics ranging from jamming in glassforming liquids, foams and granular materials, to biophysical self-assembly in actin structures and other systems. The idea of jamming is that slow relaxations in many different systems, ranging from glassforming liquids to foams and granular materials, can be viewed in a common framework. For example, one can define jamming to occur when a system develops a yield stress or extremely long stress relaxation time in a disordered state. According to this definition, many systems jam. Colloidal suspensions of particles are fluid but jam when the pressure or density is raised. Foams and emulsions (concentrated suspensions of deformable bubbles or droplets) flow when a large shear stress is applied, but jam when the shear stress is lowered below the yield stress. Even molecular liquids jam as temperature is lowered or density is increased this is the glass transition. We have been testing the speculation that jamming has a common origin in these different systems, independent of the control parameter varied. On the biophysical side, our research has been motivated recently by the phenomenon of cell crawling. When a cell crawls, its cytoskeleton--a network of filaments (primarily composed of the protein actin) that maintains the mechanical rigidity of the cell and gives the cell its shape--must reorganize in structure. This reorganization is accomplished via polymerization, depolymerization and branching of actin filaments, as well as by crosslinking the filaments together with "linker" proteins. The morphology of the resulting structure is of special interest because it determines the mechanical properties of the network. We are developing dynamical descriptions that capture morphology. In addition, we are exploring models for how actin polymerization gives rise to force generation at the leading edge.

C. P. Goodrich, A. J. Liu, and S. R. Nagel, Finite-Size Scaling at the Jamming Transition, Phys. Rev. Lett. 109 095704 (Aug. 2012). See also a Viewpoint in Physics on this paper by E. Corwin.

T. H. Harris, E. J. Banigan, D. A. Christian, C. Konradt, E. D. Tait Wonjo, K. Norose, E. H. Wilson, B. John, W. Weninger, A. D. Luster, A. J. Liu, and C. A. Hunter, Generalized Lévy walks and the role of chemokines in migration of effector CD8+ T cells, Nature 486 545 (June 2012).

L. J. Daniels, T. K. Haxton, N. Xu, A. J. Liu, and D. J. Durian, Temperature-Pressure Scaling for Air-Fluidized Grains near Jamming, Phys. Rev. Lett. 108 138001 (March 2012).

W. G. Ellenbroek, Y.-H. Wang, D. A. Christian, D. E. Discher, P. A. Jamney, and A. J. Liu, Divalent Cation-Dependent Formation of Electrostatic PIP2 Clusters in Lipid Monolayers, Biophys. J. 101 2178 (Nov. 2011).

M. Schmiedeberg, T. K. Haxton, S. R. Nagel, and A. J. Liu, Mapping the glassy dynamics of soft spheres onto hard-sphere behavior, Europhys. Lett. 96 36010 (Oct. 2011).

E. J. Banigan, M. A. Gelbart, Z. Gitai, N. S. Wingreen, and A. J. Liu, Filament Depolymerization Can Explain Chromosome Pulling During Bacterial Mitosis, PLoS Comput. Biol. 7 e1002145 (Sept. 2011).

M. L. Manning and A. J. Liu Vibrational Modes Identify Soft Spots in a Sheared Disordered Packing, Phys. Rev. Lett 107 108302 (Aug. 2011).

K. Chen, M. L. Manning, P. J. Yunker, W. G. Ellenbroek, Z. Zhang, A. J. Liu, and A. G. Yodh, Measurement of Correlations between Low-Frequency Vibrational Modes and Particle Rearrangements in Quasi-Two-Dimensional Colloidal Glasses, Phys. Rev. Lett. 107 108301 (Aug. 2011).

N. Xu, D. Frenkel, and A. J. Liu, Direct Determination of the Size of Basins of Attraction of Jammed Solids, Phys. Rev. Lett. 106 245502 (June 2011).

T. K. Haxton, M. Schmiedeberg, and A. J. Liu, Universal jamming phase diagram in the hard-sphere limit, Phys. Rev. E 83 031503 (Mar. 2011).

P. J. Yunker, K. Chen, Z. Zhang, W. G. Ellenbroek, A. J. Liu, and A. G. Yodh, Rotational and Translational Phonon Modes in Glasses Composed of Ellipsoidal Particles, Phys. Rev. E 83 011403 (Jan. 2011).

A. J. Liu and S. R. Nagel, The Jamming Transition and the Marginally Jammed Solid, Annu. Rev. Condens. Matter Phys. 1 347 (Aug. 2010).

K. Chen, W. G. Ellenbroek, Z. Zhang, D. T. N. Chen, P. J. Yunker, C. Brito, O. Dauchot, S. Henkes, W. van Saarloos, A. J. Liu, and A. G. Yodh, Low-Frequency Vibrations of Soft Colloidal Glasses, Phys. Rev. Lett. 105 025501 (July 2010).

T. K. Haxton and A. J. Liu, Kinetic heterogeneities at dynamical crossovers, Europhys. Lett. 90 66004 (June 2010).

N. Xu, V. Vitelli, A. J. Liu, and S. R. Nagel, Anharmonic and quasi-localized vibrations in jammed solids - Modes for mechanical failure Europhys. Lett. 90 56001 (May 2010).

Y. Shokef and A. J. Liu, Jamming Mechanisms and Density Dependence in a Kinetically-Constrained Model, Europhys. Lett. 90 26005 (Apr. 2010)

V. Vitelli, N. Xu, M. Wyart, A. J. Liu, and S. R. Nagel, Heat transport in model jammed solids, Phys. Rev. E 021301 (Feb. 2010).

N. Xu, T. K. Haxton, A. J. Liu, and S. R. Nagel, Equivalence of glass transition and colloidal glass transition in the hard-sphere limit, Phys. Rev. Lett. 103 245701 (Dec. 2009).

A. Souslov, A. J. Liu, and T. C. Lubensky, Elasticity and response in nearly isostatic periodic lattices, Phys. Rev. Lett. 103 205503 (Nov. 2009).

D. A. Christian, A. Tian, W. G. Ellenbroek, I. Leventhal, K. Rajagopal, P. A. Janmey, A. J. Liu, T. Baumgart, and D. E. Discher, Spotted vesicles, striped micelles and Janus assemblies induced by ligand binding, Nature Materials 8 843 (Oct. 2009).