Dielectric Effects in Dynamical Self-Assembly of Anisotropic Colloids

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TECHNICAL SUMMARYThe Chemistry Division and Division of Materials Research contribute funds to this award. It supports theoretical and computation research and education on the self-assembly of colloidal particles, objects with sizes in the range 1 to 1000 nanometers, in suspension. This is a phenomenon of widespread interest, as it enables creation of materials with novel structures. Computer simulations of these systems usually ignore the presence of polarization charges at the surfaces of the colloids, induced by ions and other charged particles in solution. This research program focuses on including polarization effects in the theoretical description by developing efficient algorithms to calculate dielectric and induced magnetic effects in colloids. These methods will be used to understand and predict the dynamics and self-assembly of suspended dielectric and magnetic colloids under the influence of the external fields. The PI aims to significantly accelerate methods to compute induced charges that arise at surfaces separating regions of different dielectric constant. The developed techniques will be extended to account for induced magnetic interactions, which are subject to a very similar mathematical formalism. The resulting algorithm will be ported to LAMMPS, one of the most widely used molecular dynamics simulation packages and part of the software cyberinfrastructure of the materials research community.This new methodology will be applied to control colloidal assembly, in which time-dependent external magnetic and electric fields could be used to induce interactions resulting in structures far from equilibrium. This research will be conducted in close collaboration with experimental groups. Furthermore, new methods will be used to uncover how electrostatically bound aggregates in biological systems are affected by dielectric mismatch. In particular, the effect of polarization charges on the stability of biological, electrostatically assembled aggregates will be examined for a range of systems, notably DNA bundles. The self-assembly phenomena studied in the context of this research will become a part of the undergraduate classes. The research itself will involve high-school students, undergraduates, and graduate students. Students working on research projects will learn modern computational and theoretical techniques. NONTECHNICAL SUMMARYThe Chemistry Division and Division of Materials Research contribute funds to this award. It supports theoretical and computation research and education on the self-assembly of colloidal particles, objects with sizes in the range 1 to 1000 nanometers, in suspension, a nanometer is about 100,000 times smaller than the diameter of a human hair. Self-assembly enables the creation of materials with novel structures and properties. Whereas computer simulations of these systems are now commonplace, they overwhelmingly ignore the presence of polarization charges at the surfaces of the colloids; polarization changes arise in response to ions and other charged particles in the solution. This research project will make possible the efficient simulation of these mobile dielectric or polarizable objects.New algorithms will be developed and applied to design new approaches to colloidal assembly, in which applied magnetic and electric fields that vary in time are used to control self-assembly. These methods will be used to study how dielectric effects affect electrostatic aggregation in biological systems.The proposed simulation methods will have an impact beyond the scope of this project by enabling the study of broad classes of systems ranging from soft condensed-matter systems to biologically relevant solutions. Furthermore, the self-assembly phenomena studied in the context of this research will become part of undergraduate classes. The research will involve high-school students, undergraduates, and graduate students.