Chemically specifi C multiscale modeling of clay-polymer nanocomposites reveals intercalation dynamics, tactoid self-assembly and emergent materials properties

A quantitative description is presented of the dynamical process of polymer intercalation into clay tactoids and the ensuing aggregation of polymerentangled tactoids into larger structures, obtaining various characteristics of these nanocomposites, including clay-layer spacings, out-of-plane clay-sheet bending energies, X-ray diffractograms, and materials properties. This model of clay-polymer interactions is based on a three-level approach, which uses quantum mechanical and atomistic descriptions to derive a coarse-grained yet chemically specifi c representation that can resolve processes on hitherto inaccessible length and time scales. The approach is applied to study collections of clay mineral tactoids interacting with two synthetic polymers, poly(ethylene glycol) and poly(vinyl alcohol). The controlled behavior of layered materials in a polymer matrix is centrally important for many engineering and manufacturing applications. This approach opens up a route to computing the properties of complex soft materials based on knowledge of their chemical composition, molecular structure, and processing conditions.This work was funded in part by the EU FP7 MAPPER project (grant number RI-261507) and the Qatar National Research Fund (grant number 09–260–1–048). Supercomputing time was provided by PRACE on JUGENE (project PRA044), the Hartree Centre (Daresbury Laboratory) on BlueJoule and BlueWonder via the CGCLAY project, and on HECToR and ARCHER, the UK national supercomputing facility at the University of Edinburgh, via EPSRC through grants EP/F00521/1, EP/E045111/1, EP/I017763/1 and the UK Consortium on Mesoscopic Engineering Sciences (EP/L00030X/1). The authors are grateful to Professor Julian Evans for stimulating discussions during the course of this project. Data-storage and management services were provided by EUDAT (grant number 283304)

Lattice Gas Automata for Reactive Systems

Reactive lattice gas automata provide a microscopic approachto the dynamics of spatially-distributed reacting systems. After introducing the subject within the wider framework of lattice gas automata (LGA) as a microscopic approach to the phenomenology of macroscopic systems, we describe the reactive LGA in terms of a simple physical picture to show how an automaton can be constructed to capture the essentials of a reactive molecular dynamics scheme. The statistical mechanical theory of the automaton is then developed for diffusive transport and for reactive processes, and a general algorithm is presented for reactive LGA. The method is illustrated by considering applications to bistable and excitable media, oscillatory behavior in reactive systems, chemical chaos and pattern formation triggered by Turing bifurcations. The reactive lattice gas scheme is contrasted with related cellular automaton methods and the paper concludes with a discussion of future perspectives.Comment: to appear in PHYSICS REPORTS, 81 revtex pages; uuencoded gziped postscript file; figures available from [email protected] or [email protected]

Etude microscopique et aspects thermodynamiques du chaos chimique

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

Numerical modeling of radiation effects in solids: Principal features, limitations and perspectives

International audienceThis paper focuses on atomistic computer modeling of radiation effects with special emphasis on the achievements of this approach as well as on its space and time scales inherent limitations. These last are the principal motivations for the development of a multiscale approach ideally consisting in a succession of models providing input information to the model acting at the immediate next time and space scales. Some methodologies used to bridge the gap between multiple space and time scales are considered together and reasons encountered preventing the approach from being predictive are examined. Moreover, we briefly comment methods improving modeling of radiation in solids

Sensitivity of non-linear dynamical systems to fluctuations: Hopf bifurcation and chaos

The statistical properties of non-linear dynamical systems are studied using the master equation approach. Detailed analysis of a model system undergoing a Hopf bifurcation reveals a non-trivial interference between macroscopic behaviour and microscopic dynamics in spatially extended systems. The effect of intrinsic fluctuations in the regime of homogeneous deterministic chaos is also analysed and the robustness of the macroscopic description is confirmed. © 1995 Società Italiana di Fisica.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Particle simulation of chemical chaos

A microscopic computer experiment is set up to investigate the statistical properties of a homogeneous chemical system undergoing chaos at the macroscopic level. A specific model, the Willamowski-Rössler having a well-defined microscopic counterpart is used. Quantitative comparison with both the prediction of the deterministic description based on the rate equations and the results of the stochastic analysis is carried out. Dynamical and static properties obtained from these three procedures are in very good agreement and confirm the robustness of the underlying deterministic attractor even when microscopic aspects are taken into account. © 1996 American Institute of Physics.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Stochastic description of a period-2 limit cycle

The effect of internal noise on the period-2 behavior is investigated in low-dimensional dynamical systems. To treat the morphological complexity of such attractors, a general stochastic formulation using a suitable moving frame in the Gaussian approximation is set up. Its applicability is illustrated on a specific model, the Willamowski-Rössler chemical scheme. Using this approach, we are able to interpret the direct simulations of the master equation which show significant changes with respect to the deterministic behavior. Specifically, a band merging in the multi-periodic regime which at first sight seems to disrupt the bifurcation cascade is observed. Marked inhomogeneities in the fluctuations distribution along the period-2 attractor explaining these features are brought out

Interfacial layering and capillary roughness in immiscible liquids

International audienceThe capillary roughness and the atomic density profiles of extended interfaces between immiscible liquids are determined as a function of the interface area by using molecular dynamics and Lennard-Jones (12-6) potentials. We found that with increasing area, the interface roughness diverges logarithmically, thus fitting the theoretical mean-field prediction. In systems small enough for the interfacial roughness not to blur the structural details, atomic density profiles across the fluid interface are layered with correlation length in the range of molecular correlations in liquids. On increasing the system size, the amplitude of the thermally excited position fluctuations of the interface increases, thus causing layering to rapidly vanish, if density profiles are computed without special care. In this work, we present and validate a simple method, operating in the direct space, for extracting from molecular dynamics trajectories the ``intrinsic'' structure of a fluid interface that is the local density profile of the interface cleaned from capillary wave effects. Estimated values of interfacial properties such as the tension, the intrinsic width, and the lower wavelength limit of position fluctuations are in agreement with results collected from the literature. (C) 2010 American Institute of Physics. [doi:10.1063/1.3471384