Thomas Ihle and Daniel Kroll, North Dakota State University DMR and DMR Mesoscale Simulations of Complex Liquids Computational studies of complex liquids, soft materials and bio- materials are demanding because of the presence of disparate length and energy scales. The goal of this project is to contribute to the understanding of these systems through the development and application of quantitative mesoscale simulation methods which incorporate both hydrodynamic interactions and thermal fluctuations. We have developed a thermodynamically consistent simulation method for binary mixtures where the fluid is described by particles which follow simple and computationally efficient ``repulsion’’ rules between particles of different type. ``Amphiphilic’’ rigid rods act as surfactants; after adding them to a phase-separated mixture, spontaneous emulsification to a microemulsion is observed. In order to study active actin gels and the dynamics of microtubules our code was extended by molecular motor complexes which stochastically attach to embedded fibers and organize them into complex patterns such as asters and bundles. Such active systems are not well understood, and we want to systematically study the influence of several effects on the patterns and their dynamics. Simulation of a fluctuating microemulsion after surfactants were added to a 50/50 binary mixture. The blue surfactants sit on the boundary between the two phases. Asters can form if fibers are embedded in a fluid and pairs of molecular motors attach and move along the fibers. E. Tuzel, G. Pan, T. Ihle, D.M. Kroll, Europhys. Letters 70 (2007) 40010, T. Ihle, E. Tuzel, Progress in Comp. Fluid Dynamics 8 (2008) 138.

Thomas Ihle and Daniel Kroll, North Dakota State University DMR and DMR Mesoscale Simulations of Complex Liquids Broader Impact Three undergraduate physics students, Andrew Buck, Mason Swanson, and William Casper did research projects associated with this grant. They were trained to program in C and developed coarse-grained algorithms for fluid mixtures and objects embedded in fluid-particle models. In doing their projects, they also learned several concepts in mechanics, statistical mechanics and fluid dynamics. Together with Benjamin Stottrup from Augsburg College the first annual undergraduate poster session at NDSU Department of Physics was organized. Erkan Tüzel was trained as a graduate student and research associate in our group and participated in almost all of our recent work on the development of mesoscale simulation techniques. There is a long standing collaboration with Gerhard Gompper from the FZ Jülich, Germany, which led to an invited review article in the journal ``Advances in Polymer Science’’, authored by Gerhard Gompper, Roland Winkler and the PI’s. Thomas Ihle worked several weeks as a visiting researcher at the MPI- PKS in Dresden, Germany and collaborated with Frank Jülicher and Stephan Grill on simulations of active networks. Simulation of sedimenting spheres with short range attraction. Molecular motor complexes swim in a fluid, attach to fibers and create a bundle network.