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

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.

scholarly journals An Expedient SERS Strip Tactic for Rapid On-Site Detection with Long-Time Sensitivity and Repeatability

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Chen Wang ◽  
Yueqian Wan ◽  
Yong Su ◽  
Yafei Cai ◽  
Shengjun Xiong ◽  
...  
Keyword(s):  
Colloidal Particles ◽  
Rhodamine 6G ◽  
Surface Enhanced Raman Spectroscopy ◽  
Dip Coating ◽  
Animal Blood ◽  
Discrimination Capability ◽  
Time Sensitivity ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Long Time

Surface-enhanced Raman spectroscopy (SERS) has attracted lots of interest in academic and industrial fields in recent years. The improvement in long-time sensitivity and repeatability is highly demanded by the on-site applications. Herein, we present an expedient SERS strip tactic with these desired advantages. Specifically, the tactic utilized the outstanding stability of colloidal particles to maintain the SERS materials during the storage. Upon usage, the strip is rapidly prepared on-site, and then the targets were sampled with a dip-coating and heating method, which is designed to standardize the whole detection process with the sensitivity kept. Thanks to the tactic, only one-third of SERS sensitivity decay was observed for rhodamine 6G after half a year. Besides rhodamine 6G, the SERS spectra of different animal blood samples were also investigated with the SERS strip tactic, and a species-based discrimination capability was preliminarily demonstrated.

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

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.

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