scholarly journals Microscopic Theory of Long-Time Center-of-Mass Self-Diffusion and Anomalous Transport in Ring Polymer Liquids

2020 ◽  
Vol 53 (23) ◽  
pp. 10431-10445
Author(s):  
Baicheng Mei ◽  
Zachary E. Dell ◽  
Kenneth S. Schweizer
Keyword(s):  
Center Of Mass ◽  
Microscopic Theory ◽  
Anomalous Transport ◽  
Self Diffusion ◽  
Polymer Liquids ◽  
Long Time ◽  
Ring Polymer

scholarly journals Non-Gaussian, transiently anomalous and ergodic self-diffusion of flexible dumbbells in crowded two-dimensional environments: coupled translational and rotational motions

2021 ◽  
Author(s):  
Kolja Klett ◽  
Andrey G Cherstvy ◽  
Jaeoh Shin ◽  
Igor M Sokolov ◽  
Ralf Metzler
Keyword(s):  
Relative Motion ◽  
Center Of Mass ◽  
Scaling Exponent ◽  
Two Dimensional ◽  
Particle Structure ◽  
Self Diffusion ◽  
Experimental Systems ◽  
Long Time ◽  
Non Gaussian ◽  
Dynamics Simulations

We employ Langevin-dynamics simulations to unveil non-Brownian and non-Gaussian center-of-mass self-diffusion of massive flexible dumbbell-shaped particles in crowded two-dimensional solutions. We also study the intra-dumbbell dynamics due to the relative motion of the two constituent elastically-coupled disks. Our main focus is on effects of the crowding fraction φ and the particle structure on the diffusion characteristics. We evaluate the time-averaged mean-squared displacement (TAMSD), the displacement probability-density function (PDF) and the displacement autocorrelation function (ACF) of the dimers. For the TAMSD at highly crowded conditions of dumbbells, e.g., we observe a transition from the short-time ballistic behavior, via an intermediate subdiffusive regime, to long-time Brownian-like spreading dynamics. The crowded system of dimers exhibits two distinct diffusion regimes distinguished by the scaling exponent of the TAMSD, the dependence of the diffusivity on φ, and the features of the displacement-ACF. We attribute these regimes to a crowding-induced transition from a viscous to a viscoelastic diffusion medium upon growing φ. We also analyze the relative motion in the dimers, finding that larger φ suppress their vibrations and yield strongly non-Gaussian PDFs of rotational displacements. For the diffusion coefficients D(φ) of translational and rotational motion of the dumbbells an exponential decay with φ for weak and a power-law D(φ) ∝ (φ - φ*)2.4 for strong crowding is found. A comparison of simulation results with theoretical predictions for D(φ) is discussed and some relevant experimental systems are overviewed.

Self-diffusion of bimodal suspensions of hydrodynamically interacting spherical particles in shearing flow

1994 ◽  
Vol 281 ◽  
pp. 51-80 ◽  
Author(s):  
Chingyi Chang ◽  
Robert L. Powell
Keyword(s):  
Diffusion Coefficients ◽  
Cluster Size ◽  
Near Field ◽  
Spherical Particles ◽  
Random Structure ◽  
Shearing Flow ◽  
Self Diffusion ◽  
Long Time ◽  
Mobility Matrix ◽  
Many Body Interactions

We study the average mobilities and long-time self-diffusion coefficients of a suspension of bimodally distributed spherical particles. Stokesian dynamics is used to calculate the particle trajectories for a monolayer of bimodal-sized spheres. Hydrodynamic forces only are considered and they are calculated using the inverse of the grand mobility matrix for far-field many-body interactions and lubrication formulae for near-field effects. We determine both the detailed microstructure (e.g. the pair-connectedness function and cluster formation) and the macroscopic properties (e.g. viscosity and self-diffusion coefficients). The flow of an ‘infinite’ suspension is simulated by considering 25, 49, 64 and 100 particles to be one ‘cell’ of a periodic array. Effects of both the size ratio and the relative fractions of the different-sized particles are examined. For the microstructures, the pair-connectedness function shows that the particles form clusters in simple shearing flow due to lubrication forces. The nearly symmetric angular structures imply the absence of normal stress differences for a suspension with purely hydrodynamic interactions between spheres. For average mobilities at infinite Péclet number, Ds0, our simulation results suggest that the reduction of Ds0 as concentration increases is directly linked to the influence of particle size distribution on the average cluster size. For long-time self-diffusion coefficients, Ds∞, we found good agreement between simulation and experiment (Leighton & Acrovos 1987 a; Phan and Leighton 1993) for monodispersed suspensions. For bimodal suspensions, the magnitude of Ds∞, and the time to reach the asymptotic diffusive behaviour depend on the cluster size formed in the system, or the viscosity of the suspension. We also consider the effect of the initial configuration by letting the spheres be both organized (size segregated) and randomly placed. We find that it takes a longer time for a suspension with an initially organized structure to achieve steady state than one with a random structure.

Long-time self-diffusion of charged spherical colloidal particles in parallel planar layers

2014 ◽  
Vol 140 (24) ◽  
pp. 244116 ◽  
Author(s):  
Claudio Contreras-Aburto ◽  
César A. Báez ◽  
José M. Méndez-Alcaraz ◽  
Ramón Castañeda-Priego
Keyword(s):  
Colloidal Particles ◽  
Self Diffusion ◽  
Long Time

scholarly journals Long-time self-diffusion in quasi-two-dimensional colloidal fluids of paramagnetic particles

2020 ◽  
Vol 101 (4) ◽  
Author(s):  
Nima H. Siboni ◽  
Alice L. Thorneywork ◽  
Alicia Damm ◽  
Roel P. A. Dullens ◽  
Jürgen Horbach
Keyword(s):  
Two Dimensional ◽  
Self Diffusion ◽  
Colloidal Fluids ◽  
Long Time

A Kinetic Monte Carlo Approach for Self-Diffusion of Pt Atom Clusters on a Pt(111) Surface

2011 ◽  
Vol 10 (4) ◽  
pp. 920-939 ◽  
Author(s):  
R. Deák ◽  
Z. Néda ◽  
P. B. Barna
Keyword(s):  
Monte Carlo ◽  
Interatomic Potential ◽  
Kinetic Monte Carlo ◽  
Center Of Mass ◽  
Elastic Band ◽  
Self Diffusion ◽  
Embedded Atom ◽  
Atom Clusters ◽  
Detailed Statistical Analysis ◽  
Simple Scaling

AbstractA lattice Kinetic Monte Carlo (KMC) approach is considered to study the statistical properties of the diffusion of Pt atom clusters on a Pt(111) surface. The interatomic potential experienced by the diffusing atoms is calculated by the embedded atom method and the hopping barrier for the allowed atomic movements are calculated using the Nudged Elastic Band method. The diffusion coefficient is computed for various cluster sizes and system temperatures. The obtained results are in agreement with the ones obtained in previous experimental and theoretical works. A simple scaling argument is proposed for the size dependence of the diffusion coefficient’s pre-factor. A detailed statistical analysis of the event by event KMC dynamics reveals two important and co-existing mechanisms for the diffusion of the cluster’s center of mass. At low temperatures (below T = 400K) the dominating mechanism responsible for the displacement of the cluster’s center of mass is the periphery (or edge) diffusion of the atoms. At high temperatures (above T = 800K) the dissociation and recombination of the clusters becomes more and more important.

Chemotaxis of Mesenchymal Stem Cells in a Microfluidic Device

2012 ◽  
Vol 1498 ◽  
pp. 67-72
Author(s):  
Ruth Choa ◽  
Manav Mehta ◽  
Kangwon Lee ◽  
David Mooney
Keyword(s):  
Stem Cells ◽  
Mesenchymal Stem Cells ◽  
Microfluidic Device ◽  
Soft Lithography ◽  
Center Of Mass ◽  
Cell Movement ◽  
Microfluidic Devices ◽  
Chemokine Gradient ◽  
Long Time ◽  
Stable Linear

ABSTRACTAdult bone marrow derived mesenchymal stem cells (MSCs) represent an important source of cells for tissue regeneration. Control of MSC migration and homing is still unclear. The goal of this study was to identify potent chemoattractants for MSCs and characterize MSC chemotaxis using a microfluidic device as a model system and assay platform. The three chemokines compared in this study were CXCL7, CXCL12, and AMD 3100.Microfluidic devices made of polydimethysiloxane (PDMS) were fabricated by soft lithography techniques and designed to generate a stable linear chemokine gradient. Cell movements in response to the gradient were captured by timelapse photos and tracked over 24 hours. Chemokine potency was measured via several chemotaxis parameters including: velocity in the direction of interest (V), center of mass (Mend), forward migration indice (YFMI). The migratory paths of the cells were mapped onto a displacement plot and compared.The following results were measured in the direction of interest (towards higher concentrations of chemokine): For velocity, only cells exposed to CXCL12 had a statistically significant (p=.014) average velocity (V=0.19 ± 0.07 um/min) when compared to the control condition (V=0.06 ±0 .04 um/min). For the center of mass, where the displacement of cells from their starting positions were compared, again only CXCL12 (Mend= 53.9 ± 10.8 um) stimulated statistically significant (p = .013) displacement of cells compared to the control condition (Mend = 19.3 ± 16.1 um). For the forward migration index, the efficiency of cell movement was measured. Indices in both the CXCL12 (YFIM = 0.19 ± 0.08) and CXCL7 (YFIM = 0.09 ±0.03) conditions were statistically significant (p = .023 for CXCL12 and p = .035 for CXCL7) when compared with the control index (YFIM = .04 ± .02).This study demonstrated the use of microfluidic devices as a viable platform for chemotaxis studies. A stable linear chemokine gradient was maintained over a long time scale to obtain cell migration results. CXCL12 was quantitatively determined to be the most potent chemoattractant in this research; these chemoattractive properties promote its use in future developments to control MSC homing.

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