Dissipative Particle Dynamics simulation of colloidal suspensions (original) (raw)
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Computer Physics Communications, 2014
In the Dissipative Particle Dynamics (DPD) simulation of suspension, the fluid (solvent) and colloidal particles are replaced by a set of DPD particles and therefore their relative sizes (as measured by their exclusion zones) can affect the maximal packing fraction of the colloidal particles. In this study, we investigate roles of the conservative, dissipative and random forces in this relative size ratio (colloidal/solvent). We propose a mechanism of adjusting the DPD parameters to properly model the solvent phase (the solvent here is supposed to have the same isothermal compressibility to that of water).
Journal of Molecular Modeling, 2002
We report results of numerical simulations of complex fluids, using a combination of discrete-particle methods. Our molecular modeling repertoire comprises three simulation techniques: molecular dynamics (MD), dissipative particle dynamics (DPD), and the fluid particle model (FPM). This type of model can depict multi-resolution molecular structures (see the found in complex fluids ranging from single micelle, colloidal crystals, large-scale colloidal aggregates up to the mesoscale processes of hydrodynamical instabilities in the bulk of colloidal suspensions. We can simulate different colloidal structures in which the colloidal beds are of comparable size to the solvent particles. This undertaking is accomplished with a two-level discrete particle model consisting of the MD paradigm with a Lennard-Jones (L-J) type potential for defining the colloidal particle system and DPD or FPM for modeling the solvent. We observe the spontaneous emergence of spherical or rod-like micelles and their crystallization in stable hexagonal or worm-like structures, respectively. The ordered arrays obtained by using the particle model are similar to the 2D colloidal crystals observed in laboratory experiments. The micelle shape and its hydrophobic or hydrophilic character depend on the ratio between the scaling factors of the interactions between colloid-colloid to colloid-solvent. Unlike the miscellar arrays, the colloidal aggregates involve the colloid-solvent interactions prescribed by the DPD forces. Different from the assump-tion of equilibrium growth, the two-level particle model can display much more realistic molecular physics, which allows for the simulation of aggregation for various types of colloids and solvent liquids over a very broad range of conditions. We discuss the potential prospects of combining MD, DPD, and FPM techniques in a single three-level model. Finally, we present results from large-scale simulation of the Rayleigh-Taylor instability and dispersion of colloidal slab in 2D and 3D. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.
Chemical Engineering Science, 2004
Dissipative particle dynamics (DPD) is a method for simulating complex uid ows and other, colloidal phenomena. It is a mesoscopic method, in that it does not rely on a continuum-level description of matter, but nor does it completely capture molecular-level detail. As such, it o ers the possibility of capturing some degree of molecular-level detail, while conforming to continuum hydrodynamics at larger length scales. We have tested the applicability of DPD to ÿnite-Reynolds-number ows by studying a series of model problems involving ow around spheres and cylinders. Our study is the ÿrst to consider explicitly the e ect of ÿnite inertia in DPD simulations. Both ow around immobile objects and the translation and rotation of mobile objects are considered. For our test problems, we show that under computationally feasible conditions DPD simulations are quantitatively accurate up to Reynolds numbers of 50-100. Typically the physical cause of inaccuracies at higher Reynolds numbers is the onset of compressibility e ects, which can be anticipated by making reference to a DPD Mach number. In addition, in our implementation of DPD, some new methods are introduced that result in the computation time scaling linearly with the number of DPD particles. It is also shown that improvements in accuracy can be realized by making use of the specular re ection boundary condition at solid-uid interfaces.
Journal of Physics: Condensed Matter, 1996
The rheological properties of colloidal suspensions of spheres and rods have been studied using dissipative particle dynamics (DPD). We have measured the viscosity as a function of shear rate and volume fraction of the suspended particles. The viscosity of a 30 vol% suspension of spheres displays characteristic shear-thinning behaviour as a function of shear rate. The values for the low-and high-shear viscosity are in good agreement with experimental data. For higher paniculate densities, good results are obtained for the high-shear viscosity, although the viscosity at low shear rates shows a dependence on the size of the suspended spheres. Dilute suspensions of rods show an intrinsic viscosity which is in excellent agreement with theoretical results. For concentrated rod suspensions, the viscosity increases with the third power of the volume fraction. We find the same scaling behaviour as Doi and Edwards for the semidilute regime, although the explanation is unclear. The DPD simulation technique therefore emerges as a useful tool for studying the rheology of paniculate suspensions.
Modelling thrombosis using dissipative particle dynamics method
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2008
Aim . Arterial occlusion is a leading cause of cardiovascular disease. The main mechanism causing vessel occlusion is thrombus formation, which may be initiated by the activation of platelets. The focus of this study is on the mechanical aspects of platelet-mediated thrombosis which includes the motion, collision, adhesion and aggregation of activated platelets in the blood. A review of the existing continuum-based models is given. A mechanical model of platelet accumulation onto the vessel wall is developed using the dissipative particle dynamics (DPD) method in which the blood (i.e. colloidal-composed medium) is treated as a group of mesoscale particles interacting through conservative, dissipative, attractive and random forces. Methods . Colloidal fluid components (plasma and platelets) are discretized by mesoscopic (micrometre-size) particles that move according to Newton's law. The size of each mesoscopic particle is small enough to allow tracking of each constituent of the...
Simulation of Suspensions in Constricted Geometries by Dissipative Particle Dynamics
Mol. Simm., 2003
We investigate the flow of a suspension through a constriction by means of the mesoscopic technique known as dissipative particle dynamics (DPD). The dispersed phase was modeled as a set of soft spheres interacting through a conservative force while suspended and continuum phases interact via DPD forces. It is shown that a Poiseuille steady state is achieved in the presence of bounding walls and under a pressure gradient in a cylindrical pipe. Flow geometry in the laminar regime is explored and discussed for periodic conditions in the presence of a cylindrical narrowing or constriction.
Dissipative particle dynamics simulations for biological tissues: rheology and competition
Physical Biology, 2011
The characteristic shape changes observed in the growth and division of L-form cells have been explained by several theoretical studies and simulations using a vesicle model in which the membrane area increases with time. In those theoretical studies, characteristic shapes such as tubulation and budding were reproduced in a non-equilibrium state, but it was not possible to incorporate deformations that would change the topology of the membrane. We constructed a vesicle model in which the area of the membrane increases using coarse-grained particles and analyzed the changes in the shape of growing membrane by the dissipative particle dynamics (DPD) method. In the simulation, lipid molecules were added to the lipid membrane at regular time intervals to increase the surface area of the lipid membrane. As a result, it was found that the vesicle deformed into a tubular shape or a budding shape depending on the conditions for adding lipid molecules. This suggests that the difference in the place where new lipid molecules are incorporated into the cell membrane during the growth of L-form cells causes the difference in the transformation pathway of L-form cells.
Simulation of advanced microfluidic systems with dissipative particle dynamics
Microfluidics and Nanofluidics, 2009
Computational Fluid Dynamics (CFD) is widely and successfully used in standard design processes for microfluidic lTAS devices. But for an increasing number of advanced applications involving the dynamics of small groups of beads, blood cells or biopolymers in microcapillaries or sorting devices, novel simulation techniques are called for. Representing moving rigid or flexible extended dispersed objects poses serious difficulties for traditional CFD schemes. Meshless, particle-based simulation approaches, such as Dissipative Particle Dynamics (DPD) are suited for addressing these complicated flow problems with sufficient numerical efficiency. Objects can conveniently be represented as compound objects embedded seamlessly within an explicit model for the solvent. However, the application of DPD and related methods to realistic problems, in particular the design of microfluidics systems, is not well developed in general. With this work, we demonstrate how the method appears when used in practice, in the process of designing and simulating a specific microfluidic device, a microfluidic chamber representing a prototypical bead-based immunoassay developed in our laboratory (Glatzel et al. 2006a, b; Riegger et al. 2006). Keywords Dissipative particle dynamics Á Simulation of microfluidic systems Á Lab on a chip Thomas Steiner: born Glatzel.
Dissipative Particle Dynamics (DPD): An Overview and Recent Developments
Archives of Computational Methods in Engineering, 2014
Dissipative particle dynamics (DPD) is a mesoscale particle method that bridges the gap between microscopic and macroscopic simulations. It can be regarded as a coarse-grained molecular dynamics method suitable for larger time and length scales. It has been successfully applied to different areas of interests, especially in modeling the hydrodynamic behavior of complex fluids in mesoscale. This paper presents an overview on DPD including the methodology, formulation, implementation procedure and some related numerical aspects. The paper also reviews the major applications of the DPD method, especially in modeling (1) micro drop dynamics, (2) multiphase flows in microchannels and fracture networks, (3) movement and suspension of macromolecules in micro channels and (4) movement and deformation of single cells. The paper ends with some concluding remarks summarizing the major features and future possible development of this unique mesoscale modeling technique.