The Grzybowski Group - Self Assembly and Adaptive Systems

Although virtually all of our experiments are supported by physical models and theoretical arguments, we are also interested in several areas of fundamental importance where theory is the primary focus and experiments play only a supporting role. First is our exploration of nanoionics where “macroscopic” interactions, such as electrostatics and van der Waals forces, compete with “molecular” interactions, such as hydrogen bonding and solvation forces. Here, we combine continuum models, such as the Poisson-Boltzmann equation and the Lifshitz theory of van der Waals forces, with discrete models, such Monte Carlo methods and Molecular Dynamics simulations, to identify the unique characteristics of self-assembly at the nanoscale (Nano Lett. 2007, much more to come soon).

At the macroscale, our theoretical team (Kyle, Siowling, Nicolas, Konstantin and Paul) is attacking the fundamental – and outstanding -- question of dynamic self-assembly (DySA, J. Phys. Chem. B 2006), in which components organize and function spontaneously far from thermodynamic equilibrium (that is, only when they are “fed” external energy). In recent years, we have pioneered rational design of experimental systems belonging to this category and have been developing them for novel engineering applications (e.g., self-assembling micromachines, Appl. Phys. Lett. 2004, microfluidic devices, Proc. Roy. Soc. 2004, as well as adaptive and reconfigurable nanomaterials, PNAS, to appear soon). Our theoretical work on DySA work builds on the foundations of nonequilibrium thermodynamics and we seek to develop a set of universal variational principles governing DySA across all length scales. Our theoretical research often involves elements of fluid dynamics (calculation of flows –fields and dissipation spectra in fluidic systems), dynamic systems theory (phase-space portraits, Lyapunov exponents) and lattice-gas simulations.

Dynamic self assembly in living (top row) and artificial (bottom row) systems. (i) A cancer cell we made triangular by appropriate surface patterning (see our Bio research for details) (ii) A bacterial colony and (iii) A school of fish. Although we have a fishtank in the lab, our fish do not want to school yet. We are trying to convince them to do so. (iv) A dynamic oscillon in a granular material. This picture comes from our colleague, Prof. Ottino. We work on granular materials in which particles are charged (cf. Nature Materials 2003 and J.Phys. Chem. B 2005 and the movie link showing how such particles such particles crystallize when shaken). (v) A pair of magnetic spinners interacting by vortex-vortex interactions. We do lot’s of cool modeling of these systems. For experiments, see Bartosz’ papers (with Prof. George Whitesides from 2000-2003). (vi) And finally, little pieces of polymer floating on an interface and “communicating” by releasing some magic chemicals. This chemical communication gives rise to dynamic patterns similar to those observed in bacterial colonies. For detail of these fascinating “artificial bacteria”, ask Siow-Ling Soh, our guru fluid mechanician.