David Jasnow

Professor

Department of Physics and Astronomy

University of Pittsburgh

Contacts:

            Phone: (412)-624-9029      E-mail: jasnow@pitt.edu

Research Group Members

Bin W. Zhang, PhD student

Rene Hurka, PhD Student

Currently working with the following postdocs in the Balazs/Jasnow Group:

Dr. Rolf Verberg

Dr. Kurt Smith

Dr. Olga Kuksenok

Principal Research Collaborators at the University of Pittsburgh

Prof. A. C. Balazs, Department of Chemical and Petroleum Engineering

Prof. Daniel Zuckerman, Department of Computational Biology

Research Background

My background and earliest research involved theoretical investigations of critical phenomena and phase transitions.  Soon my work evolved to include interfacial phenomena, that is, the statics and near equilibrium dynamics of the diffuse interfacial regions separating coexisting phases near criticality.  More recently my research turned to more decidedly nonequilibrium phenomena such as pattern formation, interfacial dynamics, phase separation kinetics and self-organization.  While I maintain interest and activity in these areas, other efforts at present involve a collaborative, multidisciplinary program in complex fluids, coarse-grained fluid mechanics including microfluidics and some new activities in complex systems and biological physics.

Polymer statistical physics and complex fluids

 My collaboration with Prof. A. C. Balazs of the Chemical Engineering Department here at the University of Pittsburgh began on a high note and has continued successfully for over a decade.  Our first collaborative effort yielded an interesting and useful result, that cheaper random copolymers do about as well in reducing the interfacial tension at the boundary between homopolymers as tailored multiblocks, which are difficult to synthesize and expensive.  This work was cited in the American Physical Society (APS) News as a significant contribution in adhesion.  Our more recent work on fracture, after publication in a physics journal, was cited in Trends in Polymer Science. Additional significant work involved a dimpling transition in a brush as solvent quality is varied and the phase behavior of random comb copolymers.

Later research turned, in part, to developing appropriate kinetic equations for viscoelastic materials, such as polymer solutions and blends, and to a description of kinetics of structured fluids such as microemulsions.  Here one focus was phase behavior under flow conditions, so that work falls under a broader category of nonequilibrium phase transitions. The conceptual issues involve the interplay between flow and chain elasticity; from the more practical perspective much processing of modern materials takes place in the presence of flow fields.  Research continues on the relation of mesoscale patterns to macroscale properties when elasticity or viscoelasticity plays an important role in the kinetics of phase separation.  The group also had a leading program of research on the properties of filled polymeric materials, for example, a blend of diblock copolymers with nanoscale hard particle additives.  This class of materials shows rich behavior owing to the coupling of separate self-organizing capabilities of the background copolymeric matrix and the entropically driven system of particles.

Some current research in the group seeks to harness entropic effects, such as depletion forces, to develop functioning “smart” materials, which can repair defects, such as fractures, with minimal outside intervention. Problems involving smart materials including self-repair, are multidisciplinary in their very nature requiring, for example, materials physics expertise combined with knowledge of developments in control systems and (self-) organization.

Coarse-grained hydrodynamics and microfluidics

A variety of problems in soft condensed matter involving fluids derive their interest in the interplay of hydrodynamic flow with situations in which the physics of diffuse interfacial regions plays an important role. In these situations traditional multiphase hydrodynamics with boundary conditions imposed on infinitely sharp interfaces will not always suffice.  Examples in which coarse-grained hydrodynamics are of value include the description of thermo-capillary driven motion of interfacial structures in thermal gradients, and in such phenomena as coalescence or engulfing of droplets, in which topological changes occur and in which local free-energetics on the scale of the diffuse interfacial thickness can play a crucial role.   A second methodology that has proven to be valuable in a variety of physical contexts is the so-called lattice-Boltzmann method. These methods have been applied in collaboration with the Balazs group to model fluid flow in media with compliant boundaries. Several bio-mimetic processes are receiving study using these methods.  Additional recent collaborations with the Balazs group involve microfluidics in which the interplay of diffusive dynamics, flow and interactions with walls in small systems can lead to rich and surprising behavior of the dynamical system.

The figure to the left (Kuksenok et al.) shows an example of what can happen in two-phase flow in a micro-channel when there is an interplay between diffusion and flow (advection). Under appropriate circumstances a localized perturbation at the inlet can produce periodic behavior downstream in this open, overdamped system.

Biological physics

I have an emerging research program in physics that may be termed "biology-inspired," and I am actively exploring collaborative arrangements with the biomedical community at the University of Pittsburgh.  It is quite likely that in coming years my focus will shift to this area.  Current active research involves the structure and energetics of polyelectrolytic bundles, such as double-stranded DNA in a condensed state or actin, and the kinetics of DNA packaging and ejection from bacteriophages.  Much of this research is being carried out with colleague, Prof. Joseph Rudnick (Dept. of Physics, UCLA). 

Kinetics experiments on bacteriophages and on transport in synapses are currently being carried out in this department by Prof. Xiao-lun Wu.  I expect to be involved more closely with the experimental activities in biological physics within the department.

A new project on the statistics of transition events relevant in molecular biophysics is being undertaken in collaboration with Prof. Daniel Zuckerman, a member of the faculty in the Department of Computational Biology.  We are exploring the statistics and paths for conformational transitions both in simplified mathematical models and for biologically relevant molecules. Currently, we are jointly supervising the multidisciplinary research of Physics Ph. D. student, Bin W. Zhang.

To the left is shown an abstraction of a condensed, charged bundle of polyelectrolytic molecules, depicted as rods, with a crystalline arrangement of adsorbed counterions (the spheres). As the system is compressed the counterion crystal can undergo a series of structural transitions to maintain electrostatic stability (Rudnick and Jasnow, PRE 68: 051902 (1968)). Similar conditions could apply to bundles of biologically interesting molecules.

Other research directions

A variety of phenomena that transcend traditional fields share similar mathematical structures and features of nonequilibrium.  Some of these might loosely be grouped under the heading of self-organization, and examples might include sand piles, aspects of evolutionary biology, flow of capital in an international economy and the behavior of social insects. I anticipate that my future research activities will explore nonequilibrium phenomena in this wider context; this is fully consistent with the view that in the coming years some of the new thinking in physics will continue to be driven by phenomena revealed in biological and other contexts.

Selected Recent Publications and Preprint Titles

"Effective potential, critical point scaling, and the renormalization group," J. Rudnick, W. Lay and D. Jasnow, Phys. Rev. E: 58, 2902 (1998).

"Shear instabilities of freely standing thermotropic smectic-A films, "H.-Y. Chen and D. Jasnow, Phys. Rev. Letters:85, 2957 (2000).

"Interface and contact line motion in a two-phase fluid under shear flow," H.-Y. Chen, D. Jasnow and J. Viñals, Phys. Rev. Letters: 85, 1686 (2000).

"Forming supramolecular networks from nanoscale rods in binary, phase-separating mixtures," G. Peng, F. Qiu, V.V. Ginzburg, D. Jasnow, and A. C. Balazs, Science 288: 1802 (2000).

"Layer dynamics of freely standing smectic-A films," H.-Y. Chen and D. Jasnow, Phys. Rev. E 61: 493 (2000).

``Multi-scale Model for Binary Mixtures Containing Nanoscopic Particles,'' Balazs, A. C., Ginzburg, V., Qiu, F., Peng, G., and Jasnow, D., requested "Focus Article,” J. Phys. Chem. B 104: 3411 (2000).

 ``Spinodal decomposition of a binary fluid with fixed impurities," F. Qiu, G. Peng, V. V. Ginzburg, A. C. Balazs, H-Y. Chen and D. Jasnow, J. Chem. Phys. 115: 3779-3784 (2001).

``Self-Assembly of Binary Particle Mixtures in Diblock Copolymers," Lee, J. Y., Thompson, R., Jasnow, D. and Balazs, A. C., J. Chem. Soc., Faraday Discussions 123: (2002).

``Entropically Driven Formation of Hierarchically Ordered Nanocomposites," Lee, J. Y., Thompson, R., Jasnow, D. and Balazs, A. C., Phys. Rev. Lett. 89: 155503 (2002).

``Binary Hard Sphere Mixtures in Block Copolymer Melts," Thompson, R., Lee, J. Y., Jasnow, D. and Balazs, A. C., Phys. Rev. E. 66: 031801 (2002).

 ``Effect of Nanoparticles on Mesophase Formation in Diblock Copolymers," Lee, J. Y., Thompson, R., Jasnow, D. and Balazs, A. C., Macromolecules 35: 4855 (2002).

``Periodic Droplet Formation in Chemically Patterned Microchannels,'' O. Kuksenok, D. Jasnow, J. Yeomans and A. C. Balazs, Phys. Rev. Letters 91: 108303 (2003).

``Diffusive Intertwining of Two Fluid Phases in Chemically Patterned Microchannels,'' O. Kuksenok, D. Jasnow and A. C. Balazs, Phys. Rev. E. 68: 051505 (2003).

"Cohesive Energy, Stability and Structural Transitions in Polyelectrolyte Bundles," J. Rudnick and D. Jasnow, cond-mat/0207651; Phys. Rev. E 68: 051902 (2003).

“Newtonian fluid meets an elastic solid: Coupling lattice Boltzmann and lattice-spring models,” Phys. Rev. E 71: 056707 (2005)

(updated 9/2005)