Thermodynamics and Hydrodynamics of Anisotropic Colloids

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TECHNICAL SUMMARY This award supports computational and theoretical research and education to develop greatly accelerated and enhanced simulation methods for suspensions of anisotropic colloids.Significant progress has been made in the fabrication of colloids with anisotropic interactions, that is, particles with aspherical shapes and/or inhomogeneous surface chemistry. One of the goals of such research is to control the structure of self-assembled materials through manipulation of the building blocks. However, it has proven difficult to correlate the nature of individual colloids with the structure of the resulting aggregates. Computer simulations are able to guide and interpret experimental work, but currently deal almost exclusively with idealized, monodisperse systems. From the experimental perspective, it has become clear that an important route towards the design of complex structures arises from the combination of multiple components, rather than from the use of a single highly complicated type of building block. The PI aims to bridge this gap by means of new computational methods that can span a wide range of time and length scales that are inaccessible to current algorithms. A focus of this work will be on developing a new class of highly efficient cluster Monte Carlo algorithms and to extend and apply simulation methods for the hydrodynamics of colloids in suspension. A second shortcoming of current modeling efforts is the neglect of kinetic effects due to the solvent. "Patchy" interactions can cause particles to remain trapped in nonequilibrium states, and hydrodynamic interactions determine the pathways along which particles encounter each other. The PI plans to extend recent techniques for the inclusion of hydrodynamics to systems containing colloids with anisotropic boundary conditions and interactions. Jointly, these two developments would provide a comprehensive framework for the modeling of hydrodynamics and thermodynamics of multicomponent systems of anisotropic colloids. This framework will be exploited to gain physical insights and make direct connections to experiments. The PI will continue to work in close collaboration with experimentalists.The simulation methods developed in this research will have an impact beyond the scope of this program by facilitating the computational study of broad classes of complex fluids, ranging from soft condensed-matter systems to biologically relevant solutions. Cluster algorithms are now routinely incorporated in the simulation course taught by the PI to undergraduates of various backgrounds, bringing new methods to the classroom. The PI has initiated and will continue a strong educational outreach program involving teaching basic science classes to adult students pursuing a high-school diploma and introductory thermodynamics to second-chance students at Harper College, a community college in Palatine, Illinois.NONTECHNICAL SUMMARYThis award supports computational and theoretical research and education to develop greatly accelerated and enhanced simulation methods for particles of various shapes suspended in fluids. These materials systems, or colloids, can be used to fabricate materials with novel properties starting from building block particles that are some ten thousand or more times smaller than the diameter of a human hair. Because of the way the particles interact in the fluid, they can assemble themselves into a material. Experimentalists seek to engineer the building blocks and the fluid environment to achieve a material with desired properties. Computer simulations hold promise to guide and possibly design materials based on this method. So far, computer simulations have largely focused on spherical particles. The PI aims to develop new simulation techniques that can accommodate particles of different shapes. The shape of the particle is controlled by its geometry and the nature of its interactions with other particles. The simulation methods will also include the fluid in which the particles are suspended. The PI also aims to overcome the need for simulation methods that can properly include processes that occur over a wide range of length and time scales. The work will be carried out in close connection with experimentalists.This is fundamental research to understand through computation how particles organize themselves in solution. It contributes to the broader effort of exploiting this knowledge to develop new ways to fabricate materials with novel properties and using computation to enable their purposeful design. The realization of this capability would have a significant impact on American competitiveness. The simulation methods developed in this research will have an impact on the computational study of other complex fluids in other disciplines, notably chemistry and biology. The PI will continue to incorporate algorithms developed in the course of this research into the simulation course that he teaches to undergraduates of various backgrounds. The PI has initiated, and will continue, a strong educational outreach program involving teaching basic science classes to adult students pursuing a high-school diploma and introductory thermodynamics to second-chance students at Harper College, a community college in Palatine, Illinois.