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2002
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Glotzer SC, Gebremichael Y, Lacevic N, Schroder TB, Starr FW
Spatially heterogeneous dynamics in liquids near their glass transition
LIQUID DYNAMICS: EXPERIMENT, SIMULATION, AND THEORY ACS SYMPOSIUM SERIES 820: 214-227 2002
[x] Liquids near their glass transition are dynamically heterogeneous, and experiments and simulations have uncovered much about the rich and complex nature of this heterogeneity. This paper highlights key results from our computer simulation studies of spatially heterogeneous dynamics (SHD) in supercooled liquids near their glass transtion. We speculate on the relationship between SHD and other phenomena ubiquitous to glasses and their liquids, and outline several outstanding questions in this Field.
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Mallamace F, Glotzer SC, Malescio G, Poole PH, Salvetti G
Horizons in complex systems - In honor of Professor H. Eugene Stanley on the occasion of his 60th birthday - Preface
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS 314 (1-4): XV- NOV 1 2002
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Lacevic N, Starr FW, Schroder TB, Novikov VN, Glotzer SC
Growing correlation length on cooling below the onset of caging in a simulated glass-forming liquid
PHYSICAL REVIEW E 66 (3): Art. No. 030101 Part 1, SEP 2002
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View Abstract
We present a calculation of a fourth-order, time-dependent density correlation function that measures higher-order spatiotemporal correlations of the density of a liquid. From molecular dynamics simulations of a glass-forming Lennard-Jones liquid, we find that the characteristic length scale of this function has a maximum as a function of time which increases steadily beyond the characteristic length of the static pair correlation function g(r) in the temperature range approaching the mode coupling temperature from above. This length scale provides a measure of the spatially heterogeneous nature of the dynamics of the liquid in the alpha-relaxation regime.
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Starr FW, Sastry S, Douglas JF, Glotzer SC
What do we learn from the local geometry of glass-forming liquids?
PHYSICAL REVIEW LETTERS 89 (12): Art. No. 125501 SEP 16 2002
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We examine the local geometry of a simulated glass-forming polymer melt. Using the Voronoi construction, we find that the distributions of Voronoi volume P(u(v)) and asphericity P(a) appear to be universal properties of dense liquids, supporting the use of packing approaches to understand liquid properties. We also calculate the average free volume [u(f)] along a path of constant density and find that [u(f)] extrapolates to zero at the same temperature T-0 that the extrapolated relaxation time diverges. We relate [u(f)] to the Debye-Waller factor, which is measurable by neutron scattering.
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Donati C, Franz S, Glotzer SC, Parisi G
Theory of non-linear susceptibility and correlation length in glasses and liquids
JOURNAL OF NON-CRYSTALLINE SOLIDS 307: 215-224 SEP 2002
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Within the framework of the effective potential theory of the structural glass transition, we calculate for the p-spin model and for a hard sphere liquid in the hypernetted chain approximation a static non-linear susceptibility related to a four-point density correlation function, and show that it diverges in mean field with exponent gamma = 1/2 as the critical temperature T-c is approached from below. When T-c is approached from above, we calculate for the p-spin model a time dependent non-linear susceptibility and show that there is a characteristic time where this susceptibility has a maximum, and that this time grows with decreasing T. This susceptibility diverges as T-c is approached from above, and has key features in common with a generalized susceptibility related to particle displacements, previously introduced to measure correlated particle motion in simulations of glass-forming liquids.
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Glotzer SC, Paul W
Molecular and mesoscale simulation methods for polymer materials
ANNUAL REVIEW OF MATERIALS RESEARCH 32: 401-436 2002
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Polymers offer a wide spectrum of possibilities for materials applications, in part because of the chemical complexity and variability of the constituent molecules, and in part because they can be blended together with other organic as well as inorganic components. The majority of applications of polymeric materials is based on their excellent mechanical properties, which arise from the long-chain nature of the constituents. Microscopically, this means that polymeric materials are able to respond to external forces in a broad frequency range, i.e., with a broad range of relaxation processes. Computer simulation methods are ideally suited to help to understand these processes and the structural properties that lead to them and to further our ability to predict materials properties and behavior. However, the broad range of timescales and underlying structure prohibits any one single simulation method from capturing all of these processes. This manuscript provides an overview of some of the more popular computational models and methods used today in the field of molecular and mesoscale simulation of polymeric materials, ranging from molecular models and methods that treat electronic degrees of freedom to mesoscopic field theoretic methods.
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Glotzer SC, Gebremichael Y, Lacevic N, Schroder TB, Starr FW
Glass-forming liquids and polymers: with a little help from computational statistical physics
COMPUTER PHYSICS COMMUNICATIONS 146 (1): 24-29 JUN 15 2002
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Starr FW, Schroder TB, Glotzer SC
Molecular dynamics simulation of a polymer melt with a nanoscopic particle
MACROMOLECULES 35 (11): 4481-4492 MAY 21 2002
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We perform molecular dynamics simulations of a bead-spring polymer melt surrounding a nanoscopic particle. We explore the effect of the polymer/nanoparticle interactions, surface-to-volume ratio, and boundary conditions on both the structure and dynamics of the polymer melt. We find that the chains near the nanoparticle surface are elongated and flattened and that this effect is independent of the interaction for the range of interactions we study. We show that the glass transition temperature T-g of the melt can be shifted to either higher or lower temperatures by tuning the interactions between polymer and nanoparticle. A gradual change of the polymer dynamics approaching the nanoparticle surface causes the change in the glass transition. The magnitude of the shift is exaggerated by increasing fraction of surface monomers in the system. These behaviors support a "many-layer"-based interpretation of the dynamics. Our findings appear applicable to systems in which surface interactions dominate, including both traditional and nanofilled polymer melts, as well as systems with markedly different geometries, such as ultrathin polymer films. In particular, we show how our results might be compared with those obtained from experimental studies of "bound" polymer.