Even Hard-Sphere Colloidal Suspensions Display Fickian Yet Non-Gaussian Diffusion

Guan, Juan; Wang, Bo; Granick, Steve

doi:10.1021/nn405476t

Cited by 138 publications

(178 citation statements)

References 90 publications

(151 reference statements)

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“…Motivated by recent experiments on the tracer diffusion in polymeric materials [16,17,22], we investigate the tracer diffusion in a polymer solution by molecular dynamics simulations.…”

Section: Discussionmentioning

confidence: 99%

Tracer diffusion in a sea of polymers with binding zones: mobile vs. frozen traps

Samanta

Chakrabarti

2016

Soft Matter

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We use molecular dynamics simulations to investigate the tracer diffusion in a sea of polymers with specific binding zones for the tracer. These binding zones act as traps. Our simulations show that the tracer can undergo normal yet non-Gaussian diffusion under certain circumstances, e.g, when the polymers with traps are frozen in space and the volume fraction and the binding strength of the traps are moderate.In this case, as the tracer moves, it experiences a heterogeneous environment and exhibits confined continuous time random walk (CTRW) like motion resulting a nonGaussian behavior. Also the long time dynamics becomes subdiffusive as the number or the binding strength of the traps increases. However, if the polymers are mobile then the tracer dynamics is Gaussian but could be normal or subdiffusive depending on the number and the binding strength of the traps. In addition, with increasing binding strength and the number of the polymer traps, the probability of the tracer being trapped increases. On the other hand, removing the binding zones does not result trapping, even at comparatively high crowding. Our simulations also show that the trapping probability increases with the increasing size of the tracer and for a bigger tracer with the frozen polymer background the dynamics is only weakly nonGaussian but highly subdiffusive. Our observations are in the same spirit as found in many recent experiments on tracer diffusion in polymeric materials and questions the validity of Gaussian theory to describe diffusion in crowded environment in general.

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“…Motivated by recent experiments on the tracer diffusion in polymeric materials [16,17,22], we investigate the tracer diffusion in a polymer solution by molecular dynamics simulations.…”

Section: Discussionmentioning

confidence: 99%

Tracer diffusion in a sea of polymers with binding zones: mobile vs. frozen traps

Samanta

Chakrabarti

2016

Soft Matter

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“…[1][2][3][4][5] Relevant applications include gas and molecule separations, 6 water purification membranes, 7 barrier materials, self-healing systems based on microcapsules, [8][9][10] ion and solute transport in polymeric materials and biological systems, 11 and the flow of colloids in porous media. 12,13 Penetrants are here, by definition, smaller than the elementary species that constitutes the matrix, but they can still vary over a wide range of absolute and relative size and shape and the extent of attractive interactions with the matrix material.…”

Section: Introductionmentioning

confidence: 99%

Correlated matrix-fluctuation-mediated activated transport of dilute penetrants in glass-forming liquids and suspensions

Zhang

Schweizer

2017

The Journal of Chemical Physics

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We formulate a microscopic, force-level statistical mechanical theory for the activated diffusion of dilute penetrants in dense liquids, colloidal suspensions, and glasses. The approach explicitly and selfconsistently accounts for coupling between penetrant hopping and matrix dynamic displacements that actively facilitate the hopping event. The key new ideas involve two mechanistically (at a stochastic trajectory level) coupled dynamic free energy functions for the matrix and spherical penetrant particles. A single dynamic coupling parameter quantifies how much the matrix displaces relative to the penetrant when the latter reaches its transition state which is determined via the enforcement of a temporal causality or coincidence condition. The theory is implemented for dilute penetrants smaller than the matrix particles, with or without penetrant-matrix attractive forces. Model calculations reveal a rich dependence of the penetrant diffusion constant and degree of dynamic coupling on size ratio, volume fraction, and attraction strength. In the absence of attractions, a near exponential decrease of penetrant diffusivity with size ratio over an intermediate range is predicted, in contrast to the much steeper, non-exponential variation if one assumes local matrix dynamical fluctuations are not correlated with penetrant motion. For sticky penetrants, the relative and absolute influence of caging versus physical bond formation is studied. The conditions for a dynamic crossover from the case where a time scale separation between penetrant and matrix activated hopping exists to a "slaved" or "constraint release" fully coupled regime are determined. The particle mixture model is mapped to treat experimental thermal systems and applied to make predictions for the diffusivity of water, toluene, methanol, and oxygen in polyvinylacetate liquids and glasses. The theory agrees well with experiment with values of the penetrant-matrix size ratio close to their chemically intuitive values. Published by AIP Publishing.

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“…The measured values of α are consistent with some simulations reported recently. 14,39 Considering the PEO mesh size is in the order of 50 nm, it is not surprised that a more significant non-Gaussianity will be observed for those NPs smaller than the typical size of the surrounding structure. The source of the non-Gaussianity will be analyzed later with the aid of the measured DPD ( Figure 3).…”

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confidence: 99%

Probing Non-Gaussianity in Confined Diffusion of Nanoparticles

Xue

Zheng

Chen

et al. 2016

J. Phys. Chem. Lett.

116

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Confined diffusion is ubiquitous in nature. Ever since the “anomalous yet Brownian” motion was observed, the non-Gaussianity in confined diffusion has been unveiled as an important issue. In this Letter, we experimentally investigate the characteristics and source of non-Gaussian behavior in confined diffusion of nanoparticles suspended in polymer solutions. A time-varied and size-dependent non-Gaussianity is reported based on the non-Gaussian parameter and displacement probability distribution, especially when the nanoparticle’s size is smaller than the typical polymer mesh size. This non-Gaussianity does not vanish even at the long-time Brownian stage. By inspecting the displacement autocorrelation, we observe that the nanoparticle–structure interaction, indicated by the anticorrelation, is limited in the short-time stage and makes little contribution to the non-Gaussianity in the long-time stage. The main source of the non-Gaussianity can therefore be attributed to hopping diffusion that results in an exponential probability distribution with the large displacements, which may also explain certain processes dominated by rare events in the biological environment.

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Even Hard-Sphere Colloidal Suspensions Display Fickian Yet Non-Gaussian Diffusion

Cited by 138 publications

References 90 publications

Tracer diffusion in a sea of polymers with binding zones: mobile vs. frozen traps

Tracer diffusion in a sea of polymers with binding zones: mobile vs. frozen traps

Correlated matrix-fluctuation-mediated activated transport of dilute penetrants in glass-forming liquids and suspensions

Probing Non-Gaussianity in Confined Diffusion of Nanoparticles

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