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Rigid Particles (rigid + particle)

Distribution by Scientific Domains

Polymers and Materials Science	85%

Selected Abstracts

Free Rotational Diffusion of Rigid Particles with Arbitrary Surface Topography: A Brownian Dynamics Study Using Eulerian Angles

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2-3 2008
Tom Richard Evensen
Abstract Rotational diffusion of rigid bodies is an important topic that has attracted sustained interest for many decades, but most existing studies are limited to particles with simple symmetries. Here, we present a simple Brownian dynamics algorithm that can be used to study the free rotational diffusion of rigid particles with arbitrary surface topography. The main difference between the new algorithm and previous algorithms is how the numerical values of the mobility tensor are calculated. The only parameters in the numerical algorithm that depend on particle shape are the principal values of the particle rotational mobility tensor. These three scalars contain all information about the surface topography that is relevant for the particle rotational diffusion. Because these principal values only need to be pre-calculated once, the resulting general algorithm is highly efficient. The algorithm is valid for arbitrary mass density distribution throughout the rigid body. In this paper, we use Eulerian angles as the generalized coordinates describing the particle angular orientation. [source]

Low Adhesive Surfaces that Adapt to Changing Environments

ADVANCED MATERIALS, Issue 18 2009
Roman Sheparovych
A responsive/adaptive nonadhesive surface coating that combines hydrophobic particles and hydrophilic polymer chains in a tethered composite coating is demonstrated. Rigid particles provide low contact area, while a selective segregation of polymer chains upon changing the surrounding environment from vapors to liquids and vice versa adapts the low-adhesive property of the composite surface. [source]

The extended finite element method for rigid particles in Stokes flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2001
G. J. Wagner
Abstract A new method for the simulation of particulate flows, based on the extended finite element method (X-FEM), is described. In this method, the particle surfaces need not conform to the finite element boundaries, so that moving particles can be simulated without remeshing. The near field form of the fluid flow about each particle is built into the finite element basis using a partition of unity enrichment, allowing the simple enforcement of boundary conditions and improved accuracy over other methods on a coarse mesh. We present a weak form of the equations of motion useful for the simulation of freely moving particles, and solve example problems for particles with prescribed and unknown velocities. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Use of the Rotation Vector in Brownian Dynamics Simulation of Transient Electro-Optical Properties

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 1 2009
Tom Richard Evensen
Abstract We have recently developed a new singularity-free algorithm for Brownian dynamics simulation of free rotational diffusion. The algorithm is rigorously derived from kinetic theory and makes use of the Cartesian components of the rotation vector as the generalized coordinates describing angular orientation. Here, we report on the application of this new algorithm in Brownian dynamics simulations of transient electro-optical properties. This work serves two main purposes. Firstly, it demonstrates the integrity of the new algorithm for BD-simulations of the most common transient electro-optic experiments. Secondly, it provides new insight into the performance of the new algorithm compared to algorithms that make use of the Euler angles. We study the transient electrically induced birefringence in dilute solutions of rigid particles with anisotropic polarization tensor in response to external electric field pulses. The use of both one single electric pulse and two electric pulses with opposite polarity are being analyzed. We document that the new singularity-free algorithm performs flawlessly. We find that, for these types of systems, the new singularity-free algorithm, in general, outperforms similar algorithms based on the Euler angles. In a wider perspective, the most important aspect of this work is that it serves as an important reference for future development of efficient BD-algorithms for studies of more complex systems. These systems include polymers consisting of rigid segments with single-segment translational,rotational coupling, segment,segment fluid-dynamic interactions and holonomic constraints. [source]

Brownian Dynamics Simulations of Rotational Diffusion Using the Cartesian Components of the Rotation Vector as Generalized Coordinates

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 7-8 2008
Tom Richard Evensen
Abstract Here, we report on the first Brownian dynamics (BD) simulations of rotational diffusion using the Cartesian components of the rotation vector as the generalized coordinates. The model system employed in this study consists of freely rotating and non-interacting rigid particles with arbitrary surface topography. The numerical BD algorithm contains no singularities and yields numerical results that are in full agreement with known theoretical results. Because of the absence of singularities, this new algorithm is several orders of magnitude more efficient than a simple BD algorithm employing the Euler angles as the generalized coordinates. The general theory for using generalized coordinates in studies of more complex systems involving both translation, rotation, and fluid dynamic interactions is well known. Consequently, the benefits reported here can readily be extended to such systems. Important examples are segmented polymer chains, with and without holonomic constraints, and liquid crystals. [source]

Free Rotational Diffusion of Rigid Particles with Arbitrary Surface Topography: A Brownian Dynamics Study Using Eulerian Angles

New nanocomposite materials made of an insulating matrix and conducting fillers: Processing and properties

POLYMER COMPOSITES, Issue 2 2000
L. Flandin
The work described in this paper deals with the preparation and the characterization of an homogeneous composite material composed of electrically conductive fillers dispersed in a thermoplastic insulating matrix. These fillers were chosen to have either a spherical shape or a high aspect ratio. Processing of these conductive polypyrrole particles, which were obtained either through a classical polymerization of pyrrole in the presence of stabilizer, or polymerization onto the surface of cellulose monocrystals is detailed. The relationship of filler content in the composite to electrical and mechanical properties was investigated. In order to characterize the connectivity of the fillers in the matrix, electrical measurements were performed and these results have been compared with the predictions of the statistical percolation theory. Further analysis was undertaken by considering the influence of the network of rigid particles on the viscoelastic properties of the composites. These results were compared with two models; first, with a mechanical percolation approach which was based on strong interactions between fillers, and second, with a mean field model, which in no way accounted for interactions bewteen fillers. In recent developments, it has been shown that these materials used as coating on various substrate could be good sensors, allowing to determine some specific features of the substrate deformation. [source]