Molecular Simulation of Disordered Materials under Stress, Daniel J. Lacks, Case Western Reserve University DMR In a broad range of condensed matter systems, one is interested in the question of how some material responds to an external mechanical load. External loads cause liquids to flow, in Newtonian or various types of non-Newtonian flows. Glassy materials, composed of polymers, metals, or ceramics, can deform under mechanical loads, and the nature of the response to loads often dictates the choice of material in various industrial applications. In biological systems, the response of proteins to external loads governs aspects of cell adhesion and muscle function. In this project, we use molecular simulations and statistical mechanics to understand this material response to external loads in a broad range of systems. As an example, our study of silica showed that the introduction of nanoscale structure can alter the atomic level structure, and can thus be used to create materials with superior mechanical properties. In particular, nanoscale structure leads to the formation of smaller silica rings (see Figure), which increases the stiffness of the material. This study was carried out in collaboration with experimentalists, who demonstrated the enhanced mechanical properties of nanostructured silica materials.

Molecular Simulation of Disordered Materials under Stress, Daniel J. Lacks, Case Western Reserve University DMR An emphasis of this project is a strong effort to mentor undergraduate student researchers. Over the 10 years of NSF support, thirteen undergraduate researchers have been co-authors on papers in peer-reviewed journals. Two of these undergraduate researchers are African-American, and five are women. Kelly Cummins (B.S., 2001) -Lei, Cummins, Lacks, “First-principles enthalpy landscape analysis of structural recovery in glasses”, J. Polym. Sci. B: Polym. Phys. 41, 2302 (2003) Nathan Duff (B.S. expected, 2007) -Duff, Wang, Mann, Lacks, “Molecular Dynamics Investigation of Bent-Core Molecules on a Water Surface”, Langmuir, in press -Duff, Duong, Lacks, “Stretching the Immunoglobulin 27 domain of the titin protein: The dynamic energy landscape”, Biophys. J., in press Brittany Isner (B.S. expected 2007) -Isner, Lacks, “Generic rugged landscapes under strain and the possibility of rejuvenation in glasses”, Phys. Rev. Lett. 96, (2006) Gerard Gagnon (B.S., 2001) -Gagnon, Patton, Lacks, “Energy landscape view of fracture and avalanches in disordered materials”, Phys. Rev. E. 64, (2001) Kaye Grant (B.S., 1998) -Roberts, Wienhoff, Grant, Lacks, "Structural transformations in silica glass under high pressure", J. Non-Cryst. Solids 281, 205 (2001) Matthew Kottemann (B.S., 2001) -Lacks, Kottemann, Yuan, “First- and second-order diatomic-to-monatomic phase transitions in a model crystal”, Chem. Phys. Lett. 347, 178 (2001) Yuning Lei (B.S., 2004) -Lei, Cummins, Lacks, “First-principles enthalpy landscape analysis of structural recovery in glasses”, J. Polym. Sci. B: Polym. Phys. 41, 2302 (2003) Djordje Nikolic (B.S., 2001) -Nikolic, Lacks, “Size scaling of mutation avalanches in a model for protein evolution”, J. Theoretical Biology 221, 259 (2003) Quyen Nguyen (B.S., 1999) -Nguyen, McGann, Lacks, "Elastic stability limits of polyethylene and n-alkane crystals from molecular simulation", J. Phys. Chem.B 103, (1999) Jaqunda Patton (B.S., 2000) -Gagnon, Patton, Lacks, “Energy landscape view of fracture and avalanches in disordered materials”, Phys. Rev. E. 64, (2001). Christopher Rives (B.S., 2002) -Rives, Lacks, “Avalanches and self-organized criticality in simulations of particle piles”, Chem. Phys. Lett. 370, 700 (2003) Madeleine Roberts (B.S., 2000) -Roberts, Wienhoff, Grant, Lacks, "Structural transformations in silica glass under high pressure", J. Non-Cryst. Solids 281, 205 (2001) Jeff Wienhoff (B.S., 1999) -Roberts, Wienhoff, Grant, Lacks, "Structural transformations in silica glass under high pressure", J. Non-Cryst. Solids 281, 205 (2001) -Lacks, Wienhoff, "Disappearances of Energy Minima and Loss of Order in Polydisperse Colloidal Systems ", J. Chem. Phys. 111, 398 (1999)